Dictionary of physics

1. 1 PHYSICS DICTIONARY Arun Umrao www.sdmsacademy.in DRAFT COPY - GPL LICENSING

2. 2 Atom A particle of matter indivisi- ble by chemical means. It is the fundamental building block of molecules. It consists of a positively charged nucleus and orbiting electrons. The number of electrons is the same as the number of protons in the nucleus. Absolute Zero It is the minimum possible temperature of the uni- verse. At absolute temperature, energy (transnational, oscillational, circular and potential) of a particle becomes purely zero. Absolute zero is 0K or −273◦ C. 100 200 300 100 −100 −200 −300 ◦ C K b −273.15◦ C b 273.15K Acceleration Acceleration determines that how fast motion of a body is changing. It is a vector quantity. Sim- ply acceleration defined as the rate of change of the velocity vector with time. d~ a = d~ v dt Activity Activity of a radioactive material is particle disintegration in one second. Activity does not depend on the environmental conditions. It depends on type of material rather than quantity of the material. Alpha Decay A radioactive element losses its atomic number by 2 and atomic mass by 4 when single particle is emitted then it is said that there is an alpha decay. Alpha decay trans- forms heavy atoms into lighter, more stable element. ZMA → Z−2NA−4 + α Alpha Particle A particle, which consists of two protons, two neutrons and no electrons. It is identical to the nucleus of a helium atom and is ejected by heavy particles undergoing alpha decay. An atom ejects alpha particle losses its atomic number by ‘2’ and mass number by ‘4’. Amplitude Amplitude is the maximum displacement of the oscillator from its equilibrium position. Ampli- tude tells how far an oscillator is swing- ing back and forth. Energy of oscillating object depends on the amplitude value. Energy-Amplitude relation is E ∝ a2 Angle Of Incidence When a light strikes on semi-transparent surface, separating two different media, it suf- fers partial reflection and partial refraction. For reflected ray, medium does not change hence angle of reflection does not change and it is equal to angle of incidence. For refracted ray, medium changes hence angle of refraction is not equal to angle of incidence. A line, perpendicular to the inter-medium boundary and passing through the point of strike by incident ray is called normal. The angle of incidence is the angle between the incident ray and the normal. Angle Of Reflection The angle between a reflected ray and the line normal to the surface. Angle Of Refraction The angle between a refracted ray and the line normal to the surface. Angular Acceleration A vector quantity, equal to the rate of change of the angular velocity vector with time. It is typically given in units of rad/s2 . Relation between instantaneous linear acceleration (a) and angular acceleration (α) is a = rα

3. 3 Angular Displacement The net change, in a point’s angular position. It is a scalar quantity. Angular Frequency A frequency, f, defined as the number of revolutions a rigid body makes in a given time interval. It is a scalar quantity commonly denoted in units of Hertz (Hz) or s−1 . Angular Momentum A vector quantity, L, that is the rotational ana- logue of linear momentum. The angular momentum is the vector product of the body’s moment of inertia, I and its angular velocity ω ~ L = I × ~ ω Angular momentum can also be ex- pressed as vector product of linear momentum, m~ v, its position from the origin, ~ r. ~ L = ~ r × m~ v Angular Period The time, T , required for a rigid body to complete one revolution. Angular period is reciprocal to the angular frequency. Angular Position Position of a particle in polar coordinate system. In polar coordinate system, there are two angle used as reference for angular position. These two angle are angle of inclination (θ) and angle of azimuth (φ). Angle of inclination is measured with respect to perpendicular axis and angle of azimuth is measured with respect to x − axis along the horizontal plane. Angular Velocity A vector quantity, that reflects the change of angular displacement with time. ω = dφ dt Unit of angular velocity is rad/s. Anti-node & Nodes When two or more waves travel in same medium simultaneously, they interfere with each other. Waves, not only travel in the medium but they also transport mechanical energy. This mechanical energy is proportional to the square of the amplitude (I ∝ A2 ). The angle value in wave equation (I = A sin θ), determines the distribution of energy of the wave in 2π range. Energy distribution pattern of all waves is different to each other due to different val- ues of angle, θ. When these two energy distributions meet at different angle (say θ1 and θ2), they suffer interference. Intensity of interfered energy depends on phase angle (φ = θ1 − θ2). If both waves meet at right opposite angle, (φ = π), then resultant intensity of two waves is zero. The point, where interference energy is zero, are called nodes. When two waves meet in same angle at a point (φ = 0), resultant intensity is maximum. This point of highest energy is called anti-node. Atom Atom is the smallest entity of any matter. It consists protons & neutrons in its nucleus and electrons in its external orbits. Atom is electri- cally neutral as number of protons and electrons are equal. Number of protons in an atom represents its atomic number and sum of masses of all con- stituting particles represents its atomic mass. There may be atoms, who have equal numbers of protons but different numbers of neutrons. These types of atom are known as isotopes collec- tively. Atoms having atomic number more than 82 are called radioactive atoms and the material is known as radioactive material. Atomic Number A number, Z, associated with the number of protons in the nucleus of an atom. Axis Of Rotation The line that every particle in the rotating rigid body circles about. Axis of rotation may or may not be inside the object.

4. 4 x y ω Barrier Potential Background Radiation The radiation found in the natural environment originating primarily from the natu- rally radioactive elements of Earth and from cosmic rays. The term may also mean radiation extraneous to an experiment. Biasing of Diode When a diode is connected with external DC source, then it is known as biasing of the diode. p n V D1 V Big Bang Beginning of the uni- verse; a transition from conditions of unimaginable density and temperature to conditions of lower density and temperature. Black-body Radiation Radiation emitted by a blackbody is called blackbody radiation. E = σT 4 Black Hole An object so dense that light cannot escape from it. Bernoulli’s Theorem A non- compressible liquid flowing streamline in a pipe of varying area of cross section. According to the Bernoulli’s theorem, total energy of liquid at every cross section in the pipe is constant. Flowing water has three types of en- ergies. (i) Pressure energy, (ii) gravitational potential energy and (iii) kinetic energy. Mathematically, for unit volume of liquid P + ρgh + 1 2 ρv2 = C Beats When two waves of slightly different frequencies interfere with one another, they produce a “beating” interference pattern that alternates between constructive (in-phase) and destructive (out-of-phase). Frequency of the beats, f, is equal to the difference in the frequencies of the two interfering waves. f = f1 ∼ f2 Beta Decay A particle, identical to an electron, emits from nucleus of a radioactive atom. The emission of beta particle from a radioactive atom is called beta decay. When beta decay occurs, atomic mass of atom does not change but its atomic number is increased by one and atom losses mass slightly. Beta Particle A particle, identical to an electron. Beta particles are ejected from an atom in the process of beta decay. Bohr Atomic Model In 1913, Niels Bohr state that, electrons revolve in fixed orbits called ground state orbits. Energy of electrons in their parental orbit is called ground state energy. Electrons can change their orbits by absorbing or emitting energy. When an electron, absorbs energy, it excited to higher energy state and jumps to higher energy orbit. After 10 nano second, it emits energy in form of photon and returns to its original orbit (ground state orbit). b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b K L M

5. 5 Brewster Angle From transparent intermedium boundaries, at brewster angle of incident, intensity of partially reflected light is zero due to its plane polarisation. The condition for brewster angle is tan θB = n2 n1 Where light is entering into medium of coefficient of refractive index n2 from medium of coefficient of refractive index n1. Bohr Radius The Bohr radius is a physical constant, approximately equal to the most probable distance between the proton and electron in a hydrogen atom in its ground state. Its value is 5.291×10−11 m. Bohr’s radius formula is a0 = 4πε0~2 mee2 Boiling Point The temperature at which a material will change phase from liquid to gas or gas to liquid. Boyle’s Law It states that at constant temperature, volume is directly proportional to the scale of absolute temperature. Mathematically PV = C 1 2 3 1 2 3 P V Bulk Modulus A coefficient (γ) that tells how much the volume of a solid will change when it is compressed. δV = γP Circuit Elements In a circuit their are three types of elements, resistive, inductive and capacitive. These elements forms the impedance of the circuit cumulatively. Capacitor Capacitor is an electrical device that can store charge for long time period. Parallel plate capacitor has capacitance of C = ǫA d Unit of capacitance of the capacitor is “farad”. ǫ is the relative permittivity of the medium inside the capacitor. Capillary Effect When a thin pipe whose diameter is negligible in respect of its length is called capillary. When it is partially immerged into the liquid, consequent of the surface tension of liquid, liquid rises inside the capillary above its level outside the capillary. Height of liquid rises or falls depends on the angle of contact and it is given by h = 2T cos θ ρgr Cyclotron Circular accelerator in which the particle is bent in traveling through a magnetic field, and an oscillating potential difference causes the particles to gain energy. Cyclotron Frequency Frequency at which the electric field is switched in order to accelerate the particles in the cyclotron. The frequency is related to the mass and charge of the particle to be accelerated. Curie (Ci) The original unit used to describe the intensity of radioactivity in a sample of material. One curie equals thirty-seven billion disintegra- tions per second, or approximately the radioactivity of one gram of radium. This unit is no longer recognized as part of the International System of units. It has been replaced by the bec- querel.

6. 6 Current Mobility In semiconductors, holes and electrons are the charge carriers and carrier mobility is electron and hole mobility. Current mobility is the consequent of the carrier mobility and is given by i = nAevd and drift velocity, vd is vd = µE. Current Density Current density is the ratio of the current to the area of cross-section of the conducting wire. Its unit is ampere per square meter. J = I A Calorie The amount of heat required to raise the temperature of one gram of water by one degree Cel- sius mainly in the range of 14.5◦ C to 15.5◦ C. One calorie is equal to 4.2 joule. Celsius A scale for measuring temperature, defined such that water freezes at 0◦ C and boils at 100◦ C. One degree Celsius is equal to one Kelvin in absolute temperature scale. Center Of Curvature A spherical mirror is formed by carving out a section from a spherical shell. The center of this spherical shell whose part the mirror is called center of curvature, (C). All of the normal pass through it. b b C Center Of Mass In motion, each body is assumed as a point mass but actual it is not a point mass. Veloc- ity, acceleration etc are measured with respect to this point mass. If a body is not a point mass then we assume a point, either inside the body mass or outside the body mass, where whole mass of the finite size body is con- centrated. The velocity and acceleration of this point is same as the velocity and acceleration of the whose body then this point is center of mass point. Mathematically, if mass particles, m1, m2, . . ., mn of finite size body of mass M are placed at distances ~ r1, ~ r2, . . ., ~ rn respectively from the origin (0, 0) then the position of center of mass is given by ~ r = m1~ r1 + m2~ r2 + . . . + mn~ rn M Center of mass is synonymous to the center of gravity. Centripetal Acceleration The acceleration of a body experiencing uniform circular motion. This acceleration is always directed toward the center of the circle. At equilibrium, a centripetal force is required to maintain the circular motion of the body. This force on a body mass m, in a uniform circular motion, in a circle of radius r is Fc = m v2 r Comparing it with F = ma, a = v2 /r and it is known as centripetal acceleration. Centripetal acceleration is not only restricted to circular paths but also measured in elliptical and parabolic paths. Centripetal acceleration in elliptic and hyperbolic paths is measured using Kepler’s law for motion of celestial objects. Centripetal Force The force necessary to maintain a body in uniform circular motion. This force is always directed radially toward the center of the circle. Mathematically Fc = m v2 r Chain Reaction The particles and energy released by the fission or fusion of one atom may trigger the fission or

7. 7 fusion of further atoms. In a chain reaction, fission or fusion is rapidly transferred to a large number of atoms, releasing tremendous amounts of energy. Charles’s Law For a gas held at constant pressure, temperature and volume are directly proportional. Vp ∝ T 1 1 2 3 T V Color Dispersion The separation of light or other radiation into individual components, usually according to frequency and wavelength. When a beam of white light passes through a prism dispersion causes it to separate into the seven colors of the rainbow. Coefficient of Viscosity Viscosity is property of fluid when it is in motion. Two different layers of fluid flowing against each other experience a re- tarding force. F = ηA dv dx Where η is the coefficient of viscosity of fluid. Coefficient Of Kinetic Friction Friction is resistance force between two layer under relative motion. The ratio between applied force and normal force to the surfaces is call coefficient of friction. F = µR Here F is applied force, R normal force between two layers and µ is coefficient of friction for the pair of two layers. It is always a number between zero and one. There are three coefficients of friction, (i) coefficient of static friction, (ii) coefficient of terminal friction and (iii) coefficient of kinetic friction. Coefficient of Thermal Expansion A object heated it expands along its dimensions. Change in its dimension is proportional to its initial value and change in temperature. For example δl = αl0 δT Here α is coefficient of thermal expansion. Coefficient Of Static Friction The coefficient of static friction, for two materials is the constant of proportionality between the normal force and the maximum force of static friction. It is always a number between zero and one. Fs = µsR Coherent Light A coherent light has all associated waves of the same wavelength and phase. To produce two sources of coherent light, they are il- luminated with single source of light. Coherent light is used in the observa- tion of interference in Young’s double slit experiment. Collision When objects collide, each object feels a force for a short amount of time. This force imparts an impulse, or changes the momentum of each of the colliding objects. The momentum of a system is conserved in all kinds of collisions. Kinetic energy is conserved in elastic collisions, but not in plastic collisions. In a perfectly plastic collision, the colliding objects stick together after they collide. Coherent Light A light beam that is defined by the individual waves vi- brating in the same phase, but not necessarily in the same plane. In order to maintain the same phase relation- ship over long distances, coherent light waves must be monochromatic (have the same wavelength). For example, laser light is highly coherent, almost

8. 8 monochromatic, and usually linearly polarized. Common Base Biasing Common Base Characteristics Common Emitter Biasing Common Emitter Characteristics Common Collector Biasing Common Collector Characteristics Component Any vector can be ex- pressed as the sum of two mutually perpendicular component vectors. For example in two dimensional plane ~ A = xî + yĵ Here î and ĵ are the unit vectors along the x−axis and y−axis. Compression An area of high air pressure that acts as the wave crest for sound waves. The spacing between successive compressions is the wavelength of sound, and the number of successive areas of compression that arrive at the ear per second is the frequency, or pitch, of the sound. Concave Lens Concave lens is also called a diverging lens. A diverging lens is thinner in the middle region than the edges. Concave lenses refract light away from a focal point and reduce the intensity of light. Image formation by the concave lens is take place according to the relation 1 v − 1 u = 1 f Here u and v are the distances of object and image from the optical point of the lens. Concave Mirror A mirror that is curved such that its center is farther from the viewer than the edges, such as the front of a spoon. Concave mirrors reflect light through a focal point. Image formation relation for this mirror is 1 v + 1 u = 1 f Conduction There are three ways of heat transfer. Conduction, convenc- tion and radiation. Heat transfer by molecular collisions is called conduction. Conservation of Angular Momen- tum If the net torque acting on a rigid body is zero, then the angular momentum of the body is constant or conserved. △L = 0 Conservation Of Momentum The principle stating that for any isolated system, linear momentum is constant with time. In case of collision either elastic or plastic, linear momentum remains conserved. Mathematically, for conserve linear momentum mv = k, d dt mv = 0 and for collision m1v1 = m2v2 Constructive Interference The am- plification of one wave by another, identical wave of the same sign. Two constructively interfering waves are said to be on phase. Convection Heat transfer via the mass movement of molecules. Gasses and liquids transfer heat by this method. Convex Lens It is also called converging lens. A lens is thicker in the middle than at the edges. Con- vex lenses refract light through a focal point. The image formed by convex lens is real except that if object is not placed between optical point and focal point of the convex lens. Converging lenses are used to intensify the distant objects and curing of distant vision of defected eye. Image formation by convex lens is 1 v − 1 u = 1 f

9. 9 Convex Mirror A mirror that is curved such that its center is closer to the viewer than the edges. Convex mirrors reflect light away from a focal point. Image formation by convex mirror is given by 1 v + 1 u = 1 f Cosine The cosine of an angle in a right triangle is equal to the length of the side adjacent to the angle divided by the length of the hypotenuse. Crest Oscillatory motion of medium particles during the propagation of transverse waves is normal to the motion of wave. The points of maximum displacement of these oscillating particles is called crest. In standing waves, a crest is also known as anti-node. The minimum displacement of oscillating particle is called trough. Critical Angle For two given media, the smallest angle of incidence at which total internal reflection occurs. Total internal reflection occurs if sin C > 1 µ Cross Product A form of vector multiplication, where two vectors are multiplied to produce a third vector. The cross product of two vectors, ~ A and ~ B, separated by an angle, θ is ~ A × ~ B = | ~ A| | ~ B| cos θn̂ where n̂ is a unit vector perpendicular to both ~ A and ~ B. Right-hand rule is used to get the direction of cross product. Mathematically, cross product also given by ~ C = ~ A × ~ B =

15. î ĵ k̂ a1 a2 a3 b1 b2 b3

21. Cycle In oscillation, a cycle occurs when an object undergoing oscillatory motion completes a “round-trip”. For instance, a pendulum bob released at angle has completed one cycle when it swings to and then back to again. In period motion, a cycle is the sequence through which a system once during each oscillation. A cycle can consist of one trip up and down for a piece of stretched string, or of a compression followed by a rarefaction of air pressure for sound waves. De Broglie Wavelength A constant that defines the speed at which a radioactive element undergoes decay. The greater λ is, the faster the element decays. Decay constant does not depends on the environmental factors but it depends on the atomic number of radioactive material as well as its concen- tration. λ = h p Here p is momentun of the object. Decibel A logorithmic unit for measuring the volume of sound. The volume of sound is the square of the amplitude of sound waves. Depletion Region After diffusion, majority charge carriers migrated to opposite region leaving minority charge carriers behind them. This causes the reversal of the charge density about the junction. The region, deep both side the junction where majority carriers are in minority is known as depletion region or depletion layer. Deposition The process by which a gas turns directly into a solid because it cannot exist as a liquid at certain pressures. Destructive Interference When two or more waves travel in same medium simultaneously, they start in- teract with each other and produce a resultant wave. Due to difference in interaction angle, the resultant wave has different amplitude and oscillating cycle to the parent waves. If phase differ-

22. 10 ence at any point of interaction of two waves is 180 degree then they cancel to each other and resultant amplitude at this point is zero. It is known as Destructive Interference. Despite the name of this phenomenon, nothing is destroyed by this interference-the two waves emerge intact once they have passed each other. Dichroic Material Materials which have different absorption for perpendicular incident planes for light are said to be dichroic. The mineral tourmaline is the best known of natural materials. Tourmaline refers to a class of boron silicates. A tourmaline crystal has a unique optic axis, and any electric field vector which is perpendicular to that axis is strongly absorbed. Po- laroid is strongly dichroic and therefore an effective polarizer. If the transmis- sion axes of ideal polarizers are perpendicular, no light is transmitted. The light tranmitted at other angles follows the Law of Malus. Dimension of Unit Dimension of unit is relationships between different physical quantities by identifying their fundamental dimensions such as length, mass, time, and electric charge. For a physical quantity, there may be one or more SI unit but every SI unit of a physical quantity has only one dimension. Diode Diode is a device that converts an alternate current into direct current and acts as rectifiers. A diode is a p-n junction diode that exhibits low resistance in forward bias and very high resistance in reverse bias. Diffusion Current Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers. Diffraction The bending of light at the corners of objects or as it passes through narrow slits or apertures. Diffraction Grating A sheet, film, or screen with a pattern of equally spaced slits. Typically the width of the slits and space between them is chosen to generate a particular diffraction pattern. Direction The property of a vector that distinguishes it from a scalar. Directly Proportional Two quantities are directly proportional if an increase in one results in a proportional increase in the other, and a decrease in one results in a proportional decrease in the other. In a formula defining a certain quantity, those quantities to which it’s directly proportional will appear in the numerator. Dispersion The separation of different color light via refraction. Red color light has lowest dispersion while blue color has highest dispersion in visible range. Displacement A vector quantity, commonly denoted by the vector s, which reflects an object’s change in spatial position. The displacement vector points from the object’s start- ing position to the object’s current position in space. If an object is moved from point A to point B in space along path AB, the magnitude of the object’s displacement is the separation of points A and B. Note that the path an object takes to get from point A to point B does not figure when defining displacement. Distance If an object is moved from point A to point B in space along path AB, the distance that the object has traveled is the length of the path AB. Distance is to be contrasted with displacement, which is simply a measure of the distance between points A and B, and doesn’t take into account the path followed between A and B. It is a scalar quantity. Drift Velocity The drift velocity is the flow velocity that a particle attains due to an electric field. Drift velocity of an electron in a conductor of length l and applied voltage V is given by vd = eV τ lm

23. 11 Drift Current Drift current is the electric current, or movement of charge carriers, which is due to the applied electric field, often stated as the elec- tromotive force over a given distance. Doppler Shift Waves produced by a source that is moving with respect to the observer will seem to have a higher frequency and smaller wavelength if the motion is towards the observer, and a lower frequency and longer wavelength if the motion is away from the observer. The speed of the waves is independent of the motion of the source. Dot Product A form of vector multiplication, where two vectors are multiplied to produce a scalar. The dot product of two vectors, A and B, is ex- pressed by the equation ~ A · ~ B. ~ A · ~ B = x1x2 + y1y2 + z1z2 Dynamics The application of kinematics to understand why objects move the way they do. More precisely, dynamics is the study of how forces cause motion. Dynamic Resistance Dynamic resistance of a transistor is ratio of the emitter base potential to the emitter current in common base configuration. It is given by rd = VEB iE Escape Velocity It is the minimum velocity of an object at the earth surface from where it is thrown never returns to the surface. Escape velocity is independent of the mass of the object. For Earth, its value is 11.2km per second. Effluent Velocity Effluent velocity is the velocity of the liquid from a hole at depth of h from the liquid level. It is given by v = p 2gh Efficiency The ratio of work done by an engine to the heat taken by it. Efficiency of a heat engine is never 100 Elastic Collision A collision in which both kinetic energy and momentum are conserved. Electrical Resonance Electrical resonance of a circuit (mainly LCR circuit) is a phenomenon at which the circuit shows peak response to the applied electric source of a suitable frequency. At resonance, the circuit is purely resistive and effective impedance of the circuit does not contain the impedance contribution of inductor and capacitor. E L C R Figure 1: A LCR circuit. Electrical Resonance Frequency At resonance, impedance of the circuit does not contain the impedance contribution of inductor and capacitor. Hence E L C R XL − XC = 0 Figure 2: A LCR circuit at resonance. XL − XC = 0 This relation gives f = 1 2π 1 √ LC

24. 12 Electrical Resonance Power Power of a resonance circuit is given by P = P0 cos φ where φ is phase factor of the resonat- ing circuit. Here P0 is power supplied to the circuit in state of resonance. cos φ for a LCR circuit is cos φ = R Z and Z = p R2 + (XL ∼ XC)2. Electric Field A charge in rest or motion, emits electric field around its space where another charge experiences electric force, F = qE. Electric field of charge +q at a distance of r from it is given by ~ E = 1 4πǫ0 × q r2 Direction of electric field is always from positive charge to negative charge. Electric Generator A device that converts mechanical energy to electrical energy by rotating a coil in a magnetic field. It is also called as dynamo. Induced emf in the electric generator is given by e = − dφ dt Electromagnetic Induction The property by which a charge moving in a magnetic field creates an electric field. Electromagnetic Spectrum The spectrum containing all the different kinds of electromagnetic waves, rang- ing in wavelength and frequency. Electromagnetic Wave A transverse traveling wave created by the oscillations of an electric field and a magnetic field. Electromagnetic waves travel at the speed of light, 3 × 108 m/s. Electron A negatively charged particle that orbits the nucleus of the atom. Its mass is 9.1 × 10−31 kg and has charge −1.6 × 10−19 C. Electronvolt A unit of measurement for energy on atomic levels. It is denoted by 1eV. Its value in joule unit is 1.6 × 10−19 joule. Energy A conserved scalar quantity associated with the state or condition of an object or system of objects. We can roughly define energy as the capacity for an object or system to do work. There are many different types of energy, such as kinetic energy, potential energy, thermal energy, chemical energy, mechanical energy, and electrical energy. Entropy It is the disorder of a system. Entropy increases with increase of chaos in the system. Euquations of Linear Motion In linear motion, height of moving object remains constant throughout its motion. There are three equations of linear motion. These are v = u + at s = ut + 1 2 at2 and v2 = u2 + 2as Where all symbols are in their usual meaning. Equilibrium The state of a non- rotating object upon whom the net torque acting is zero. Equilibrium Position The stable position of a system where the net force acting on the object is zero. Errors in Measurement During the measurement of physical quantity, there may be some errors arises due to the defects in instruments, environmental changes and wrong methods of observations etc. These errors are known as errors in measurement. Electric Dipole Moment The product of charge and distance of separation for an electric dipole. Electric

25. 13 dipole moment of an electric dipole is given by p = q × 2l Where q is magnitude of any of the two charges of the dipole and 2l is length of axis. Electromagnetic Radiation Radia- tion consisting of electric and magnetic fields that travel at the speed of light. Excited State The state of an atom or nucleus when it possesses more than its normal energy. Typically, the excess energy is released as a gamma ray. Extrinsic Semiconductor Pure semiconductor is insulator at room temperature and conductor to certain degree when temperature rises. To made it conductor, external impurities are added into it. This semiconductor is known as extrinsic semiconductor. Fermion A particle having a spin that is an odd integer multiple of ℏ/2. Fictive Temperature We know that the density of a substance changes/fluctuates with change in the temperature of the substance. Fictive temperature represents to the temperature at which the density fluctuations are “frozen” in the material. Faraday’s Electro-magnetic Law Faraday’s electromagnetic law states that (a) there is an induced electro- motive force (emf) if there is relative motion between coil and magnet. (b) The induced emf (e) is rate of change of linked flux (φ) through the coil, ie e = − d dt φ F Faraday’s constant. Its numerical value is 96000 coulomb (F). If one coulomb charge is passed through a electrolyte solution having mono- valent ions then at electrode one mole of the ionic substance is deposited. To deposit one mole material of valancy n, charge required is nF. First Law Of Thermodynamics Es- sentially a restatement of energy conservation, it states that the change in the internal energy of a system is equal to the heat added plus the work done on the system., Mathematically Q = U + W Focal Length The distance between the focal point and the vertex of a mirror or lens. For concave mirrors and convex lenses, this number is positive. For convex mirrors and concave lenses, this number is negative. Focal Point The point of a mirror or lens where all light that runs parallel to the principal axis will be focused. Concave mirrors and convex lenses are designed to focus light into the focal point. Convex mirrors and concave lenses focus light away from the focal point. Force A push or a pull that causes an object to accelerate. Mass acceleration relation for force is given by F = m × a Forward Biasing In forward biasing, p-region of the diode is connected with positive terminal of DC source and n-region is connected with negative terminal. In forward biasing, the deplation region is narrowed and junction offers negligible resistance. p n V D1 V Forward Current Characteristics Forward biasing characteristic is the graphical relation between forward potential and forward current. In forward biasing, depletion region is shortened and there is normal forward current.

26. 14 V I bc Vknee When forward potential is increased, the forward current is increases at first and then remains constant. This constant current is known as saturation current. Free-body Diagram Free body diagram illustrates all the forces acting on an object. These forces are drawn as vectors originating from the center of the object. Frequency It is the number of cy- cles executed by a system in one second. Frequency (f) is inverse of the period, T . In terms of angular frequency, ω = 2πf. Frictional Force A force caused by the roughness of two materials in contact, deformations in the materials, and a molecular attraction between the materials. Frictional forces are always parallel to the plane of contact between two surfaces and opposite the direction that the object is being pushed or pulled. Fundamental The standing wave with the lowest frequency that is supported by a string with both ends tied down is called the fundamental, or resonance, of the string. The wavelength of the fundamental is twice the length of the string. Gain (Transistor) Gravity Gravity is phenomenon of force of attraction between two masses. For example, a ball fall from the height on the surface of the earth is phenomenon of gravity. The gravitational force, consequent of gravity acts along the central axes of the mass. Gravitational Field Gravitational field of a heavy mass, M, at distance of r from the center of heavy mass is the strength of gravity by which it at- tracts to unit mass placed at distant r. For earth it is denoted by g and mathematically given by g = G M r2 Gravitational Potential Gravita- tional potential of a heavy mass, M, placed at point of distance r from the center of the heavy mass, is the work done on unit mass when it is brought from infinity to that point. Mathemat- ically given by V = G M r Graded Index Fiber In some types of optical fiber refractive index is made of vary as a function of the radial distance from the center of the fiber. Gamma Decay A form of radioactivity where an excited atom releases a photon of gamma radiation, thereby returning to a lower energy state. The atomic structure itself does not change in the course of gamma radiation. Gamma Ray An electromagnetic wave of very high frequency. The pen- etration power of gamma rays is largest among all the radiation waves emitted in radioactive decays. Gold Foil Experiment Gold foil experiment was carried out by Ernest Rutherford popularly known as alpha particle scattering. This experiment proved for the first time that atoms have nuclei. Gravitational Constant The constant of proportionality in Newton’s Law of Gravitation. It reflects the proportion of the gravitational force and the product of two particles’ masses di-

27. 15 vided by the square of the bodies’ separation. F = G mM r2 Gravitational Potential Energy The energy associated with the configuration of bodies attracted to each other by the gravitational force. It is a measure of the amount of work necessary to get the two bodies from a chosen point of reference to their present position. This point of reference is usually chosen to be a point of infinite distance, giving the equation. Objects of mass m that is at a height of h above the surface of the earth have a gravitational potential energy, mgh. Ground State In the Bohr model of the atom, the state in which an electron has the least energy and orbits closest to the nucleus. Half-life The amount of time it takes for one-half of a radioactive sample to decay. t1/2 = 0.693 k Or N = N0 1 2 n Where n is number of half years. Harmonic Series The series of standing waves supported by a string with both ends tied down. The first member of the series, called the fundamental, has two nodes at the ends and one anti-node in the middle. The higher harmonics are generated by placing an integral number of nodes at even intervals over the length of the string. The harmonic series is very important in music. Heat A transfer of thermal energy. We don’t speak about systems having heat, but about their transferring heat, much in the way that dynamical systems don’t have work, but rather for work. Heat Engine A machine that oper- ates by taking heat from a hot place, doing some work with that heat, and then exhausting the rest of the heat into a cool place. The internal com- bustion engine of a car is an example of a heat engine. Heat Transfer A transfer of thermal energy from one system to another. There are three methods of heat transfer. (i) conduction, (ii) convection and (iii) radiation. In heat transfer, conduction and convection requires medium while radiation does not re- quire medium for heat transfer. Hertz (Hz) It is unit of frequency. Its dimension is the inverse of the time. Holes Holes are the majority charge carriers in p-type extrinsic semiconductor. The motion of holes is opposite to the direction of electric field. In semiconductor, holes behave like proton and its equivalent charge is equal to the magnitude of the charge of electron. Hooke’s Law For an oscillating spring, the restoring force exerted by the spring is directly proportional to the displacement. F ∝ −x That is, the more the spring is displaced, the stronger the force that will pull toward the equilibrium position. The applied fource should be within elastic limits of the spring otherwise spring will be set to the permanent ex- tension. Hypotenuse The longest side of a right triangle, opposite to the right angle. Hypotenuse (h) is related with base (b) and height (l) as h2 = l2 + b2 Hydrogen Spectrum Hydrogen spectrum is series of electromagnetic

28. 16 waves emitted or absorbed by an electron undergoing energy level transitions. The wavelength of emitted or absorbed electromagnetic wave is given by 1 λ = Z2 R 1 n2 1 − 1 n2 2 Where Z is atomic number of atom. There are many spectrum series according to the level of transitions. First five series are the most promi- nent and they are named as Lyman, Balmer, Paschen, Bracket and Funds. Ideal Gas Law A gas law from which the volume of gas becomes zero when temperature is zero kelvin at constant pressure. It is PV = µRT Impulse A vector quantity defined as the product of the force acting on a body multiplied by the time interval over which the force is exerted. I = F × t Incident Ray When dealing with reflection or refraction, the incident ray is the ray of light before it strikes the reflecting or refracting surface. Inclined Plane A wedge or a slide. The dynamics of objects sliding down inclined planes is a popular topic on SAT II Physics. Index Of Refraction Index of refraction of medium B, in respect of medium A is the ratio of the veloci- ties of light in medium A to medium B. AnB = velocity of light in medium A velocity of light in medium B Intrinsic Semiconductor A semiconductor material is insulator in its purest form at room temperature. Its conductivity increases with increase of the temperature. This type of conduc- tive semiconductors are known as intrinsic semiconductor. Inductor Inductor is a coil with or without metallic core. Inductors offer impedance to their circuits due to their inductive properties. Inductance of inductors depends on the varying magnetic flux. This is why inductors do not offer impedance to the circuit in direct current. Induced Current The current induced in a circuit by a change in magnetic flux. Induced current is given by I × Z = − d dt φ Here Z is impedance of the circuit. Inelastic Collision A collision in which momentum is conserved but kinetic energy is not. Inertia The tendency of an object to remain at a constant velocity, or its resistance to being accelerated. New- ton’s First Law is alternatively called the Law of Inertia because it describes this tendency. Inertia of an object is given by I = Z dm x2 Where dm is mass of the element at distance x from the axis of rotation. Inertial Reference Frame A reference frame in which Newton’s First Law is true. Two inertial reference frames move at a constant velocity relative to one another. According to the first postulate of Einstein’s theory of special relativity, the laws of physics are the same in all inertial reference frames. Instantaneous Velocity Instanta- neous velocity of an object is the velocity at any given instant in time. In contrast to it average velocity is a measure of the change in displacement over a given time interval. Internal Energy The energy stored in a thermodynamic system. Internal

29. 17 energy mainly depends on the temperature of the system. It is given by dQ = dU + dW Where dU is change in internal energy due to change of small charge dQ. Inversely Proportional Two quantities are inversely proportional if an increase in one results in a proportional decrease in the other, and a decrease in one results in a proportional increase in the other. In a formula defining a certain quantity, those quantities to which it’s inversely proportional will appear in the denominator. Islanding Islanding refers to the condition in which a distributed generator continues to power a location even though electrical grid power from the electric utility is no longer present. Islanding can be dangerous to utility workers, who may not realize that a circuit is still powered, and it may prevent automatic re-connection of de- vices. For that reason, distributed gen- erators must detect islanding and im- mediately stop producing power; this is referred to as anti-islanding. Isolated System A system that no external net force acts upon. Objects within the system may exert forces upon one another, but they cannot re- ceive any impulse from outside forces. Momentum is conserved in isolated systems. Isotope Atoms of the same element may have different numbers of neutrons and therefore different masses. Atoms of the same element but with different numbers of neutrons are called isotopes of the same element. Joule The joule (J) is the unit of work and energy. One calorie is equal to 4.2 Joule. Kelvin A scale for measuring temperature, defined such that 0K is the lowest theoretical temperature a material can have. Kepler’s First Law The path of each planet around the sun is an ellipse with the sun at one focus. Kepler’s Second Law If a line is drawn from the sun to the planet, then the area swept out by this line in a given time interval is constant. Kepler’s Third Law According this law, the square of the orbital time period is directly proportional to the cube of the semi-major axis of the orbit of revolving planet. T 2 ∝ a3 Kinematic Equations The five equations used to solve problems in kinematics in one dimension with uniform acceleration. Kinematics Kinematics is the study and description of the motion of objects. Kinetic Energy Energy associated with the state of motion. The translational kinetic energy of an object is given by the equation KE = 1 2 mv2 Kinetic Friction The force between two surfaces moving relative to one another. The frictional force is parallel to the plane of contact between the two objects and in the opposite direction of the sliding object’s motion. If normal force between the two surfaces is F then friction force Ff is given by Ff = µkF Here µk is coefficient of kinetic friction. Kinetic Theory Of Gases A rough approximation of how gases work, that is quite accurate in everyday conditions. According to the kinetic theory, gases are made up of tiny, round molecules that move about in accor- dance with Newton’s Laws, and collide with one another and other objects

30. 18 elastically. We can derive the ideal gas law from the kinetic theory. Laminar Flow Laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disrup- tion between the layers. At low veloci- ties, the fluid tends to flow without lat- eral mixing, and adjacent layers slide past one another like playing cards. Latent Heat Of Fusion The amount of heat necessary to transform a solid at a given temperature into a liquid of the same temperature, or the amount of heat needed to be removed from a liquid of a given temperature to transform it into a solid of the same temperature. It is Hf = m × l Where l latent headt of fusion. Latent Heat Of Sublimation The amount of heat necessary for a material undergoing sublimation to make a phase change from gas to solid or solid to gas, without a change in temperature. Latent Heat Of Transformation The amount heat necessary to cause a substance to undergo a phase transition. Latent Heat Of Vaporisation The amount of heat necessary to transform a liquid at a given temperature into a gas of the same temperature, or the amount of heat needed to be taken away from a gas of a given temperature to transform it into a liquid of the same temperature. Hv = m × l Where l latent heat of vaporisation. Law of Floatation An object will float or not depends on the weights of object (wo) and medium (wm). If wo wm then object will float partially at the surface of the mdium. If wo = wm then object may float at any layer of the medium. And if wo wm then object will settle down at the bot- tom of the container of the medium. Law Of Conservation Of Energy Energy cannot be made or destroyed. Energy can only be changed from one place to another or from one form to another. According the law of conservation of energy for vertical plane motion of an object of mass m under the gravitational field at any given height, h 1 2 mv2 = mgh Here v is instantaneous velocity of the object at height h. Law Of Reflection For a reflected light ray. In other words, a ray of light reflects of a surface in the same plane as the incident ray and the normal, and at an angle to the normal that is equal to the angle between the incident ray and the normal. Legs The two shorter sides of a right triangle that meet at the right angle. Lenz’s Law States that the current induced in a circuit by a change in magnetic flux is in the direction that will oppose that change in flux. Using the right-hand rule, point your thumb in the opposite direction of the change in magnetic flux. The direction your fingers curl into a fist indicates the direction of the current. Linear Velocity An object moving in linear path is said to be in linear motion and its velocity at any instant of time is knwon as linear velocity. It is given by v = dx dt Linear Acceleration Linear acceleration of the object is the rate of change of velocity at any instant of time. a = dv dt

31. 19 Linear Momentum A moving object has momentum energy that remains conserved until-unless external force is not applied. Momentum of an object is given by p = mv Logic Gate A logic gate is a special form of amplifier circuit designed to input and output logic level volt- ages. Gates are represented by their own symbols rather than their transistors and resistors constituents. The inputs of logic gates are symbolised into logic levels ‘0’ and ‘1’. Output of logic gates are also measured into these logic levels. Longitudinal Waves Waves that oscillate in the same direction as the propagation of the wave. Sound is carried by longitudinal waves, since the air molecules move back and forth in the same direction the sound travels. Loudness The square of the amplitude of a sound wave is called the sound’s loudness, or volume. Magnetic Field A moving charge produces magnetic field in its field space where another current carrying conductor experiences magnetic force. From Biot-Savart law d ~ B = µ0 4π I d~ l r2 sin θ Magnetising Intensity Magnetic Susceptibility The magnetic susceptibility is a dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field. M = χvH Magnetic Flux The dot product of the area and the magnetic field passing through it. Graphically, it is a measure of the number and length of magnetic field lines passing through that area. It is measured in Webers (Wb). φ = ~ B · ~ A Magnification The ratio of the size of the image produced by a mirror or lens to the size of the original object. This number is negative if the image is upside-down. Magnitude A property common to both vectors and scalars. In the graphical representation of a vector, the vector’s magnitude is equal to the length of the arrow. Magnetic Dipole Moment The product of pole strength and distance of separation of poles of the magnet. Magnetic dipole moment of a magnet is given by M = m × 2l Where m is magnetic strength of any of the two poles of the magnet and 2l is length of magnet. Malus Law Malus law gives the intensity of light when it passes through two polarisation plates. If θ is angle between the axes of two polariods then intensity of emerging light is Iθ = I0 cos θ Margin Of Error The amount of error that’s possible in a given measurement. Mass A measurement of a body’s inertia, or resistance to being accelerated. Mass Defect The mass difference between a nucleus and the sum of the masses of the constituent protons and neutrons. Mass Number The mass number, A, is the sum of the number of protons and neutrons in a nucleus. It is very close to the weight of that nucleus in atomic mass units.

32. 20 Maxima In an interference or diffraction pattern, the places where there is the most light. Mechanical Energy The sum of a system’s potential and kinetic energy. In many systems, including pro- jectiles, pulleys, pendulums, and motion on frictionless surfaces, mechanical energy is conserved. One important type of problem in which mechanical energy is not conserved is the class of problems involving friction. Medium The substance that is displaced as a wave propagates through it. Air is the medium for sound waves, the string is the medium of transverse waves on a string, and water is the medium for ocean waves. Note that even if the waves in a given medium travel great distances, the medium itself remains more or less in the same place. Melting Point The temperature at which a material will change phase from solid to liquid or liquid to solid. Meson A class of elementary particle whose mass is between that of a proton and that of an electron. A common kind of meson is the pion. Microscope Michelson-Morley Experiment An experiment in 1879 that showed that the speed of light is constant to all ob- servers. Einstein used the results of this experiment as support for his theory of special relativity. Minima In an interference or diffraction pattern, the places where there is the least light. Two light waves produces minima if their phase difference is even multiple of π. Correspond- ing path difference should be odd multiple of λ/2. Mole Mole is unit of chemical mass measurement. One mole is equivalent to moles = Mass in gram Molar mass One mole has fixed volume and number of molecules at STP. It occupy 22.4lt volume and have 6.23 × 1023 molecules. Moment Of Inertia The moment of inertia for a single particle is MR2 , where M is the mass of the rigid body and R is the distance to the rotation axis. For rigid bodies, moment of inertia is given by I = mk2 Where k is radius of gyration. Momentum Linear momentum, p, commonly called momentum for short, is a vector quantity defined as the product of an object’s mass, m, and its velocity, v. Motor Electric motor is a device that works in direct current as well as alternate current. Electric motor converts electrical energy into mechanical energy. The power delivered by the motor is measured in torque. Power of the motor is given by P = 2πfτ Motional Emf The emf created by the motion of a charge through a magnetic field. Mutual Induction The property by which a changing current in one coil of wire induces an emf in another. If L1 and L2 are the individual self induction of the two coils then their mutual induction M is given by M = p L1L2 Neutrino An almost massless particle of neutral charge that is released along with a beta particle in beta decay. Neutron A neutrally charged particle that, along with protons, consti- tutes the nucleus of an atom. Neutron Number The number, N, of neutrons in an atomic nucleus. Newton A unit of force represented by N. On newton unit is equal to the

33. 21 product of 1kg mass and its unit acceleration. Newton’s First Law An object at rest remains at rest, unless acted upon by a net force. An object in motion remains in motion, unless acted upon by a net force. Newton’s Law Of Universal Grav- itation The force of gravity, F, between two particles of mass and , separated by a distance r, has a magnitude of , where G is the gravitational constant. The force is directed along the line joining the two particles. Newton’s Second Law Newton second law is product of mass and its acceleration. F = ma Newton’s Third Law To every action, there is an equal and opposite reaction. If an object A exerts a force on another object B, B will exert on A a force equal in magnitude and opposite in direction to the force exerted by A. Node The points on a standing wave where total destructive interference causes the medium to remain fixed at its equilibrium position. Normal The line perpendicular to a surface. There is only one normal for any given surface. Normal Force The reaction force of the ground, a table, etc., when an object is placed upon it. The normal force is a direct consequence of New- ton’s Third Law. Nuclear Fission A nuclear reaction in which a high-energy neutron bombards a heavy, unstable atomic nucleus, causing it to split into two smaller nuclei, and releasing some neutrons and a vast amount of energy at the same time. Nuclear Fusion A nuclear reaction that takes place only at very high tem- peratures. Two light atoms, often hydrogen, fuse together to form a larger single atom, releasing a vast amount of energy in the process. Nucleus The center of an atom, where the protons and neutrons reside. Electrons then orbit this nucleus. Optical Path Optical path, in the optics, is the path traveled by a light between two points. The effective length of optical path for a light ray depends on the medium in which it is traveling. Optics It is branch of the sci- ence in which properties of visible light are studies. Electromagnetic spectrum with wavelengths between 360 and 780nm is called visible light. Orbit When an object is held in circular motion about a massive body, like a planet or a sun, due to the force of gravity, that object is said to be in orbit. Objects in orbit are in perpetual free fall, and so are therefore weight- less. Oscillation A back-and-forth movement about an equilibrium position. Springs, pendulums, and other oscillators experience harmonic motion. Pascals The unit for measuring pressure. One Pascal is equal to one Newton per meter squared. Ohm’s Law Ohm’s law states that current in a circuit is directly proportional to the voltage across it. Hence i = GV Here G is conductance of the conductor. Its reciprocal is resistance. And V = iR Pendulum A pendulum consists of a bob connected to a rod or rope. At small angles, a pendulum’s motion ap- proximates simple harmonic motion as it swings back and forth without friction. Pendulum, Torsional Perfectly Non-elastic Collision A collision in which the colliding particles stick together.

34. 22 Permeability Permeability, µ, is the measure of the ability of a material to support the formation of a magnetic field within itself. Hence, it is the degree of magnetization that a material obtains in response to an applied magnetic field. In SI unit, µ0 = 4π × 10−7 H/m. Period The time required by an oscillating object to complete one cycle is time period of the oscillating object. Phase Two oscillators that have the same frequency and amplitude, but reach their maximum displacements at different times, are said to have different phases. Similarly, two waves are in phase if their crests and troughs line up exactly, and they are out of phase if the crests of one wave line up with the troughs of the other. Phase (△φ) (△x) path differences are related with each other as △φ = 2π λ × △x Phase Change When a solid, liquid, or gas changes into another phase of matter, it is said that substance undergoes phase change. Phaser Diagram Photoelectric Effect When electromagnetic radiation shines upon a metal, the surface of the metal releases energized electrons. The way in which these electrons are released contradicts classical theories of electromagnetic radiation and supports the quantum view according to which electromagnetic waves are treated as particles. Photoelectron The name of an electron released from the surface of a metal due to the photoelectric effect. Photon A small particle-like bun- dle of electromagnetic radiation. Rest mass of photon is zero while its kinetic mass is not. Energy associated with photon is hν, where ν is frequency of the photon’s wave. Photon energy is quantised hence energy magnitude of photon can not further divided into sub-parts. Pitch Pitch is a perceptual property of sounds that allows their or- dering on a frequency-related scale, or more commonly, pitch is the qual- ity that makes it possible to judge sounds as “higher” and “lower” in the sense associated with musical melodies. Pitch can only be deter- mined in sounds that have a frequency that is clear and stable enough to be distinguishable from noise. Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre. Planck’s Constant The Planck constant, h, is the proportionality constant for the relation of energy and frequency ν of an oscillating quantum particle. E = hν Its numerical value is 6.63 × 10−34 Js. Polarization A process that aligns a wave of light to oscillate in one dimension rather than two. Polarisation by Reflection Inten- sity of partially reflected light from the inter-medium surface is changes from maximum to minimum when angle of incident increases from zero to Brew- ster angle. Intensity of the reflected light is minimum to plane polarisation of the reflected light. This phenomenon is known as polarisation of light by reflection. Potential Energy Energy associated with an object’s position in space, or configuration in relation to other objects. This is a latent form of energy, where the amount of potential energy reflects the amount of energy that po- tentially could be released as kinetic energy or energy of some other form. Power Defined as the rate at which work is done, or the rate at which energy is transformed. P is measured in joules per second (J/s), or watts (W).

35. 23 Pressure Pressure is normal force on per square unit area. It is measured in N/m2 or ‘Pa’. Prism A bounded medium between two square planes is known as prism. Prism generates a spectrum of white light by dispersion phenomenon called rainbow. Principal Axis The straight line that runs through the focal point and the vertex of a mirror or lens. Projectile An object moving in vertical plane under the gravitational effect is known as projectile. Function of projectile is a function of velocity and angular direction, ie f(v, θ). Ve- locity of projectile has two component, one is horizontal component and other is vertical component. Horizontal velocity remains constant throughout the motion while vertical velocity changes with time. Proton A positively charged particle that, along with the neutron, occu- pies the nucleus of the atom. Pulley A pulley is a simple machine that consists of a rope that slides around a disk or block. Quark The building blocks of all matter, quarks are the constituent parts of protons, neutrons, and mesons. Quantisation Any physical quantity will said to be quantised if it is integer multiple of smallest known value. This phenomenon is known as quantisation. For example, charge in any body is integer multiple of magnitude of charge on electron, ie 1.6 × 10−19 coulomb. Hence charge on any object is given by Q = ne where n is number of excess or deficient electrons in that object. Radian A unit for measuring angles. It is given by θr = arc radius Relation between radian and degree is given by θr = π 180 × θd Radial Acceleration in Circular Motion Radiation Radiation is method of transfer of heat in form of radiation. Heat transfer from this method is possible in vacuum also. Radioactive Decay The process by which unstable nuclei spontaneously release particles and/or energy so as to come to a more stable arrangement. The most common forms of radioactive decay are alpha decay, beta decay, and gamma decay. Radioactivity An object is called radioactive if it undergoes radioactive decay. Radius Of Curvature With spherical mirrors, the radius of the sphere of which the mirror is a part. Rarefaction An area of high air pressure that acts as the wave trough for sound waves. The spacing between successive rarefaction is the wavelength of sound, and the number of successive areas of rarefaction that arrive at the ear per second is the frequency, or pitch, of the sound. Arrangement of Resistances In a circuit, resistances may be arranged in parallel or series arrangement. In parallel and series arrangements, equivalent resistance is given by respectively : 1 R = 1 R1 + 1 R2 + 1 R3 and R = R1 + R2 + R3 Recombination When charge carriers passes from p-type to n-type region or vice-versa, holes and electrons neutralised to each other. This phenomenon is known as recombination.

36. 24 Real Image An image created by a mirror or lens in such a way that light does actually come from where the image appears to be. If you place a screen in front of a real image, the image will be projected onto the screen. Reflect A wave on a string that is tied to a pole at one end will reflect back toward its source, producing a wave that is the mirror-image of the original and which travels in the opposite direction. Reflected Ray The ray of light that is reflected from a mirror or other reflecting surface. Reflection The phenomenon of light bouncing off a surface, such as a mirror. Reflection can occurs from any surface except it should not be a black body. When light reflects from shining surface then it is consider as reflection while reflection of the light from the rough surface is called diffused reflection. Refracted Ray The ray of light that is refracted through a surface into a different medium. Refraction bending of light as it passes from one medium to another. Light refracts toward the normal when going from a less dense medium into a denser medium and away from the normal when going from a denser medium into a less dense medium. Voltage Regulation The variation of the dc output as a function of dc load current is called voltage regulation. It is given by % regulation = Vno load − Vload Vload × 100 Here, Vno load is dc output voltage when there is no current. Vload is dc output voltage when there is normal load current. Relaxation Time Resistor Any material of any shape and size offers opposition to the flow of current through themselves. This opposition is referred as resistance of the material. From Ohm’s law R = V I Resistance of the material is due to the collision of the charge carriers with rigid atoms or ions. Based on the shape and size R = ρ l A where ρ is specific resistance of the material. Resonance Electrical circuit having resistor, inductor and capacitor is called resonant circuit. Resonant circuit has its own natural frequency given by f = 1 2π × 1 √ LC The circuit is said to be in resonance when external source has frequency of integer multiple of natural frequency of the circuit. At resonance, a LCR circuit becomes purely resistible circuit. Restoring Force The force that causes simple harmonic motion. The restoring force is always directed toward an object’s equilibrium position. Reverse Biasing In reverse biasing, p-region of the diode is connected with negative terminal of DC source and n- region is connected with positive terminal. In reverse biasing, the deplation region is widened and junction offers very high resistance. p n V D1 V Reverse Biasing Characteristics Reverse biasing characteristic is the graphical relation between reverse potential and reverse current. In reverse biasing, depletion region is widen and there is no normal current while

37. 25 there is a weak reverse current due to thermionic hole-electron generation. V I V break When reverse potential is very large, above breakdown potential, diode experiences avalanche breakdown and a very steep reverse current is observed. Right-hand Rule A means of defining the direction of the cross product vector. To find the direction, first three fingers of the right hand are placed mutually normal. If index and middle finger pointed to the direction of the vectors then thumb is in the direction of the cross product of the vectors. Rigid Body An object that retains its overall shape, meaning that the particles that make up the rigid body stay in the same position relative to one another. Rotational Kinetic Energy The energy of a particle rotating around an axis. Rotational kinetic energy is given by Er = Iω2 Rotational Motion Occurs when every point in the rigid body moves in a circular path around a line called the axis of rotation. Rutherford Nuclear Model The model of the atom according to which negatively charged electrons orbit a positively charged nucleus. This model was developed by Ernest Rutherford in light of the results from his gold foil experiment. Satellite Motion Motion of a satellite orbiting around the earth. Binding energy of the satellite came from the Newton’s force of gravitation. Orbits of a revolving satellite may be circular or elliptical. Saturation Current The maximum collector current in a transistor that does not change when emitter-base current is increases is called saturation current. For different collector potential, the saturation current level is different. Satellite Velocity It is the velocity of the satellite revolving its near circular orbits around the earth. v = r G Me r Here r is distance of satellite from the earth having mass Me. Satellite Time Period Time required by a satellite to make one complete revolution in its orbital path around the earth is called time period of the satellite. Time period of the satellite is ratio of the orbital perimeter to the orbital velocity of the satellite. T = 2πr vo Time period of the satellite varies from few hours to 24 hours. Step Index Fiber Refractive index of core of optical fiber is uniform throughout and undergoes an abrupt change at cladding boundary. This is called step-index fiber. Stoke’s Law Stokes law explains the dragging or viscous force on an object moving in homogeneous liquid with instantaneous velocity v. F = 6πηrv Here η is dynamic viscosity, r is radius of the spherical object. Stopping Potential in Photoelectric Effect In photoelectric phenomenon, ejected electrons are negative in na- ture. If we applied a negative electric field in the region in which electron is

38. 26 being ejected then electron does not leave the surface. The corresponding potential of this electric field is known as threshold potential. Energy of electron in potential V is eV and it should be equal to eV = hν − hν′ Scalar A quantity that possesses a magnitude but not a direction. Mass and length are common examples. Second Law Of Thermodynamics There are a few versions of this law. One is that heat flows spontaneously from hot to cold, but not in the reverse direction. Another is that there is no such thing as a 100% efficient heat engine. A third states that the entropy, or disorder, of a system may increase but will never decrease spontaneously. Semiconductors Materials which are insulator at low temperature and conductor at higher temperature are called semiconductors. The energy band gap of semiconductors is less than metals and more than insulators. Significant Digits The number of digits that have been accurately measured. When combining several mea- surements in a formula, the resulting calculation can only have as many significant digits as the measurement that has the smallest number of significant digits. Simple Harmonic Oscillator An object that moves about a stable equilibrium point and experiences a restoring force that is directly proportional to the oscillator’s displacement. Sine In a right triangle, the sine of a given angle is the length of the side opposite the angle divided by the length of the hypotenuse. Snell’s Law When light enters into dense medium from rare medium, it deviates towards normal to surface. Snell’s law gives relation between angle of incidence, i to the angle of refraction, r as µ = sin i sin r Here µ is refractive index of dense medium with respect to rare medium. Sound Waves carried by variations in air pressure. The speed of sound waves in air at room temperature and pressure is roughly 343m/s. Specific Heat The amount of heat of a material required to raise the temperature of either one kilogram or one gram of that material by one degree Celsius. Q = m s △t Specific Resistivity It is the property of a material and resistance of a conductor is directly proportional to the specific resistivity of the material of conductor and the shape of conductor. Now R = ρ l A Here ρ is specific resistivity. Specific Conductivity Reciprocal of specific resistivity is specific conductivity of the material. Spectroscope A device that breaks incoming light down into spectral rays, so that one can see the exact wavelength constituents of the light. Speed A scalar quantity that tells us how fast an object is moving. It measures the rate of change in distance over time. Speed is to be contrasted with velocity in that there is no direction associated with speed. Spring Objects that experience oscillatory or simple harmonic motion when distorted. Their motion is described by Hooke’s Law. Spring Constant The spring constant, k, is the constant of proportionality between the restoring force exerted by the spring, and the spring’s displacement from equilibrium. F = −kx

39. 27 The greater the value of k, more resis- tant the spring is to being displaced. Standing Wave A wave that inter- feres with its own reflection so as to produce oscillations which stand still, rather than traveling down the length of the medium. Standing waves on a string with both ends tied down make up the harmonic series. Static Friction The force between two surfaces that are not moving relative to one another. The force of static friction is parallel to the plane of contact between the two objects and re- sists the force pushing or pulling on the object. Streak Flow Strong Nuclear Force The force that binds protons and neutrons together in the atomic nucleus. Surface Tension Surface tension is the elastic tendency of liquids which makes them acquire the least surface area possible. Surface tension is given by force per unit length. T = F l Surface Energy Surface energy is the work per unit area done by the force that creates the new surface. W = T × A Sublimation The process by which a solid turns directly into gas, because it cannot exist as a liquid at a certain pressure. Superposition The principle by which the displacements from different waves traveling in the same medium add up. y = y1 + y2 + y3 + . . . Super- position is the basis for interference. System A body or set of bodies that we choose to analyze as a group. Turbulant Flow In turbulent flow, liquid particles moves in random layers when move from higher to lower surface level. Tail In the graphical representation of vectors, the tail of the arrow is the blunt end. Tangent In a right triangle, the tangent of a given angle is the length of the side opposite the angle divided by the length of the side adjacent to the triangle. Tangential Acceleration in Circular Motion Telescope An optical device used to observe distant objects. It ap- parently brought distant objects near to the observer by its magnification times. Temperature A measure of the average kinetic energy of the molecules in a system. Temperature is related to heat by the specific heat of a given substance. Tension Force The force transmitted along a rope. Its value is approximately equal to the force applied on the rope. Theory of Continuity Theory of continuity is based on the principle of volume in and volume out of non- compressible fluid through a pipe are always equals. Mathematically Av = K Where A and v are the area of cross section and velocity of the fluid at any point of cross section of the pipe. Thermal Energy The energy of the molecules that make up an object. It is related to heat, which is the amount of energy transferred from one object to another object that is a different temperature. Thermal Equilibrium Two materials are in thermal equilibrium if they are at the same temperature. Third Law Of Thermodynamics An object cannot be cooled to absolute zero. Threshold Frequency A property of a metal, the minimum frequency of electromagnetic radiation that is necessary to release photoelectrons from

40. 28 that metal. Threshold energy is given by hν′ . If a photon of energy hν falls on the surface then kinetic energy of ejected electron is the difference of the energy of photon and threshold energy. KEe = hν − hν′ Tip In the graphical representation of vectors, the tip of the arrow is the pointy end. Torque The effect of force on rotational motion. If force ~ F is applied on a rotational object at distance of ~ r from the axis of rotation then torque is given by ~ τ = ~ F × ~ r Its SI unit is Nm. Total Internal Reflection The phenomenon by which light traveling from a high n to a low n material will reflect from the optical interface if the incident angle is greater than the critical angle. Trajectory Trajectory is traverse path of projectile. Geometrically it is parabolic in shape. Transistors Transistor is a device of two junction diodes in which one type of semiconductor wafer is sand- wiched between two other type of the semiconductor material. A transistor has three terminals known as emitter, base and collector. To operate the transistor, its emitter must be forward bias while its collector must be in reverse bias. E B C Ie Ic Ib Figure 3: Structure of a PNP transistor. Transformer A device made of two coils, which converts current of one voltage into current of another voltage. In a step-up transformer, the primary coil has fewer turns than the secondary, thus increasing the voltage. In a step-down transformer, the secondary coil has fewer turns than the primary, thus decreasing the voltage. For transformer N1 N2 = V1 V2 Translational Motion The movement of a rigid body’s center of mass in space. Transverse Waves Waves in which the medium moves in the direction perpendicular to the propagation of the wave. Waves on a stretched string, water waves, and electromagnetic waves are all examples of transverse waves. Traveling Waves A wave with wave crests that propagate down the length of the medium, in contrast to station- ary standing waves. The velocity at which a crest propagates is called the wave speed. Trough The points of maximum negative displacement along a wave. They are the opposite of wave crests. Truth Table Truth table consits outputs of the a logic gate corresponding all possible inputs. The truth table is different for different logic gates. The truth table of OR gate is given be- low. A B Y=A+B 0 0 0 1 0 1 0 1 1 1 1 1 Uncertainty Principle A principle derived by Werner Heisenberg in 1927 that tells us that we can never know both the position and the momentum of a particle at any given time.

41. 29 Uniform Circular Motion The motion of a body moving in circular path is with constant speed. In uniform circular motion, centripetal force is bal- anced by tension in the string of length R. F = mv2 R Unit Vector A unit vector is a vector with length ‘1’. In two dimension, a unit vector is given by â = î + ĵ Universal Gas Constant It is represented by R. Its numerical value is 8.314J/(Kmol). Vector A vector quantity, or vector, is an object possessing, and fully described by, a magnitude and a direction. Graphically a vector is depicted as an arrow with its magnitude given by the length of the arrow and its direction given by where the arrow is point- ing. Velocity A vector quantity defined as the rate of change of the displacement vector with time. It is to be contrasted with speed, which is a scalar quantity for which no direction is spec- ified. Vertex The center of a mirror or lens. Viscosity Viscosity is property of fluid and related with the fluid- ity. Fluid that flow slowly is said to be more viscous than the fluid flows speedily. Viscosity restricts the flow of fluid. It is directly related with temperature and its value decreases when temperature increases. Virtual Image An image created by a mirror or lens in such a way that light does not actually come from where the image appears to be. Young’s Modulus A coefficient that tells how much a material will ex- pand or contract lengthwise when it is stretched or compressed. The relation is given by strain = Y × stress Here Y is coefficient of Young’s modulus. Wave A system with many parts in periodic, or repetitive, motion. The oscillations in one part cause vibrations in nearby parts. Wave Speed The speed at which a wave crest or trough propagates. Note that this is not the speed at which the actual medium moves. Wavelength The distance between successive wave crests, or troughs. Wavelength is measured in meters and is related to frequency and wave speed by Weak Nuclear Force The force in- volved in beta decay that changes a proton to a neutron and releases an electron and a neutrino. Weak Interaction The interaction responsible for all processes in which flavor changes, hence for the instabil- ity of heavy quarks and leptons, and particles that contain them. Weak in- teractions that do not change flavor (or charge) have also been observed. Weber The unit of magnetic flux. Weight The gravitational force exerted on a given mass. Weight of the object is multiple of mass and gravity. Weightlessness The experience of being in free fall. If you are in a satellite, elevator, or other free-falling object, then you have a weight of zero Newtons relative to that object. Work Done when energy is transferred by a force. The work done by a force ‘F’ in displacing an object by ‘s’ is ‘W’. W = F · s Work Function The amount of energy that metal must absorb before it can release a photo-electron from the metal.

42. 30 Work-energy Theorem States that the net work done on an object is equal to the object’s change in kinetic energy. Zeroth Law Of Thermodynamics If two systems, A and B, are in thermal equilibrium separately with C, then systems A and C are necessarily in thermal equilibrium.

Dictionary of physics

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Dictionary of physics

Similar to Dictionary of physics (20)

More from Arun Umrao

More from Arun Umrao (20)

Recently uploaded

Recently uploaded (20)

Dictionary of physics