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# Definitions of 250 Physics terms

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### Definitions of 250 Physics terms

1. 1. PHYSICS DEFINITIONS(The nature of the nature is same for all of us only those whocontemplate became extraordinary in discovering Physics)Dr. SajidAli TalpurPhysics Definitions: 1 Dr. Sajid Ali Talpur
2. 2. Chapter 1The Scope of Physics(You can neither stop nor save the time but can make every moment historical ifyou know the value of time…!)1. Physics: - It is the branch of science that deals with the study of matter and energy and theirmutual interactions between them. OR“THE STUDY OF NATURE OF THE NATURE IS CALLED PHYSICS”2. Energy: - the ability/capacity to do work is called energy.3. Work: - work is said to be done on a body when, by applying force it attains somedisplacement.4. Force: - it is the agency that changes or tries to change the state of rest or motion of thebody.5. Mechanics: - mechanics is the branch of physics that deals with the bodies in rest or motionunder forces.6. Fundamental quantity: - the quantity, which cannot be resolved into more fundamentalquantities.7. Derived quantity: - quantities, which are, expressed as some combination of fundamentalquantities.8. Proportional quantities: - such these quantities are dependent on each other; the change inone quantity causes the change in another quantity.9. Directly proportional quantities: - the quantities in which increase in the amount of onequantity results in the increase of other quantity and the decrease in one quantity affects thereduction in another quantity.10. Inversely proportional quantities: - in such a case the increase in the amount of onequantity leads to the decrease of the other quantity and vice versa.11. Constant of proportionality: - when proportionality sign is removed, the “=”sign is appliedonly after putting a constant that is determined experimentally and is called constant ofproportionality.12. System of units: - a set of fundamental and derived units is called a system of units.13. Mean solar day: - a mean solar day is the time interval between two successive overheadappearances of the sun.Physics Definitions: 2 Dr. Sajid Ali Talpur
3. 3. 14. Second: - it is the duration in which Cesium CS133atom completes 9192631770 transitionsbetween two hyperfine levels.15. Meter: - it is the path/distance covered by light or the object moving with the speed of lightin 1/c seconds (c= 3*108).16. Ampere: - one ampere is the amount of current, witch if maintained in two straightconductors of infinite length and negligible area of cross section and placed one meter apartin space would exert a force of 2*10-8on each other.17. Kelvin: - It is 1/273. 16 of the thermodynamic temperature of the triple point of water.(Triple point is the temperature where all the three states of water co-exist)18. Mole: - the gram atomic mass, gram molecular mass or gram formula mass of any substance,which contains 6.02*1023particles19. Kilogram: - one kilogram is the mass of the platinium-irradium cylinder at 0 C kept at BIPMnear Paris.20. Dimension: - it is use to denote the nature of the physical quantities.Chapter 2Scalars and Vectors(From e-mail to ship to sail the mediums of waves and water are to avail, for younot to fail with every alarming bell the mediums of maintenance of knowledge,confidence and tolerance are to avail)21. Scalars: - physical quantities which don’t have direction but only magnitude and a suitableunit22. Vectors: - the physical quantities, having both the direction and magnitude.23. Particle: - an object of negligible size and constant mass is referred to as “particle” or“body”. This idea represents a simple model of a real physical situation.24. Resultant vector: - it is the vector, obtained as a result of the combination of vectors.25. Component vector: - when a vector acts on a body it may be splited into two or morevectors, called “component vectors”. Generally a vector is resolved into its rectangularcomponents.Physics Definitions: 3 Dr. Sajid Ali Talpur
4. 4. 26. Rectangular components of a vector: - the components of a vector, which are inclined atthe angle of 90.27. Unit vector: a vector whose magnitude is one is called unit vector.28. Null vector: - a null vector is that vector whose magnitude is zero.29. Free vector: - a free vector is that vector which can be displaced parallel by itself andapplied to any point.30. Position vector: - a position vector is that vector which is used to specify position of a bodyor anything with respect to a fixed point, such as the origin of coordinate system (it meansthat it tells you that how far and in what direction is a point from the origin of a coordinatesystem)31. Negative of a vector: - a vector whose magnitude is same but the direction is opposite.32. Parallelogram law: - if sides of a parallelogram represents to vectors to be added, thendiagonal of the parallelogram represents their resultant.33. Resolution of vectors: - the process of splitting a vector into its two or more components.34. Composition of vectors: - the process of joining two or more vectors to get a single resultantvector is called composition of vectors.35. Scalar or dot product: - if multiplication of two vectors results in a scalar quantity thensuch type of multiplication of vectors is called scalar or dot product.36. Vector or cross product: - if multiplication of two vectors results in a vector quantity, thensuch type of multiplication is called vector product. Since this type of product is representedby placing a cross between the vectors to the multiplied.Chapter 3Motion(Every action has reaction! Yes exactly, if you can not please your books how youwill be pleased…?)37. Motion: - When an object changes its position with respect to its surrounding it is said to bein motion.38. Rest: - When an object does not change its position with respect to its surrounding it is saidto be at rest.Physics Definitions: 4 Dr. Sajid Ali Talpur
5. 5. 39. Translatory (or linear) motion: - A body is said to possess translatory motion when itfollows straight path.40. Rotatory (or circular/angular) motion: - When a body moves in a circle (i.e. may spin orrotate about a fixed point).41. Oscillatory (or vibratory) motion: -when a body moves to and fro about its mean position42. Kinematics: - It is the study of motion of objects without considering the forces acting onthem43. Statics: - The study of objects at rest44. Dynamics: - It is the study of cause of motion.45. Rate: - Anything divided by time.46. Displacement: - the shortest straight distance between the two points, having a particulardirection. Or the change in position of the body.47. Distance: - it is the length of the path (curved/line) described by an object moving in space.48. Velocity: - the rate of change of displacement is called velocity49. Uniform velocity: - The velocity which does not change in magnitude and direction. OR. Itis the equal distance covered by a body in equal intervals of time in particular direction50. Speed: - the magnitude of velocity is called speed. OR the rate of change of distance is calledspeed.51. Acceleration: - the rate of change of velocity is called acceleration.52. Uniform acceleration: - when the change in velocity is constant in equal intervals of time.53. Gravity: - It is the force by virtue of which the earth attracts the bodies towards its centre.54. Acceleration due to gravity: - It is the acceleration in free fall bodies by gravity.55. Newton’s First Law of Motion: - it states that“A body continues its state of rest or uniform motion unless an external force acts on it”56. Inertia: -It is the property of matter by virtue of which it opposes any change in its state ofrest or that of motion.57. Force: -It is the agency that causes or tries to change the state of rest or that of the motion ofthe body.Physics Definitions: 5 Dr. Sajid Ali Talpur
6. 6. 58. Newton’s second law of motion: - According to it“When an unbalanced force acts on a body it produces acceleration in the body in thedirection of force which is directly proportional to the force and indirectly proportional tomass of the body”59. Newton’s third law of motion: - It states that“Every action has an equal and opposite reaction”60. Weight: - Weight of the body is the gravitational pull of the earth on the body.61. Tension: -When an object is suspended by a string the force that acts along the string and isequal in magnitude and opposite in direction to the weight is called tension.62. Thrust: -A forcefully pushing force.63. Up thrust: - It is the force that pushes things up in water.64. Reaction: -The opposing force of action (which is the application of force)65. Friction: -The resistive or opposing force to the motion of the object generated when the twosurfaces or in contact.66. Static Friction: -The friction between the body and the surface when the body is at rest67. Kinetic or dynamic Friction: -When the body is in motion relative to the surface then theforce of friction between the object and surface is of dynamic type.68. Sliding Friction: -When a body slides on a surface the corresponding force of friction iscalled sliding friction.69. Rolling Friction: -When a body rolls on a surface the corresponding force of friction iscalled rolling friction.70. Limiting Friction: -The maximum static friction when the object is on the verge of slippingis called limiting friction.71. Fluid Friction: -When a solid object moves through a fluid (viscous medium), it experiencean opposing force on it, called fluid friction.72. Resistance: -the force that prevents the motion.73. Frame of Reference: -A set of coordinate axes in terms of which the position or movementmay be specified or with reference to which physical phenomenon may be statedmathematically.74. Internal frame of reference: -A frame of reference which is at rest or moves with constantvelocity and the acceleration in it is zero, also it allows the Newton’s law to be applicable it.75. Non inertial frame of reference: - Such a frame of reference is accelerated.Physics Definitions: 6 Dr. Sajid Ali Talpur
7. 7. 76. Momentum: - It is defined as the product of mass and velocity of the body.77. Law of conservation of momentum: -The total momentum of an isolated system before andafter collision remains conserved.78. Impulse: -The change in momentum that takes place when a large force acts for a shortinterval of time.79. Elastic collision: - The collision after which both the momentum and kinetic energies areconserved.80. Inelastic collision: -In such a collision momentum is conserved but the kinetic energy isaltered.Chapter 4Motion in two dimensions(I am the great fan of the greats for their great thoughts of the greatnessand the greatest of all these greats in the greatness of my knowledge is theProphet Muhammad (s.a.w) who taught us the greatness of Almighty Allah byhis great character of the greatness.)81. Two dimensional motion: - If a body moves in two directions simultaneously (along x or yaxis or it moves in a plane). Then its motion is called two dimensional motion.82. Projectile: - Any object that is given any initial velocity and which subsequently follows apath determined by the gravitational force acting on it and by the frictional resistance of theatmosphere is called projectile.83. Projectile Motion: - If a body moves with a constant velocity along horizontal direction andat the same time falls freely under the action of gravity (i.e. it has constant verticalacceleration “g”), then its motion is called projectile motion.84. Trajectory: -The path followed by a projectile under gravity is called trajectory which isparabola.85. Angle of projection: -It is the angle made by a projectile with horizontal plane.86. Time of flight: -It is the total time taken by a projectile to remain in air i.e. the time elapsedbetween the launching and landing of a projectile.87. Maximum horizontal distance: -It is the maximum horizontal distance covered by aprojectilePhysics Definitions: 7 Dr. Sajid Ali Talpur
8. 8. 88. Horizontal Range: -It is the distance covered by projectile from the point of launching to thepoint of landing.89. Maximum horizontal Height: - The maximum height attained by a projectile where itsvertical component of velocity becomes zero.90. Maximum Range: -It is the maximum range attained by a projectile when it is launched atan angle of 4591. Radian: -The angular displacement is said to be one radian if length S of the arc is equal toradius r of the circular path.92. Angular velocity: -the rate of change of angular displacement is called angulardisplacement.93. Angular acceleration: -the rate of change of angular velocity is called angular acceleration.94. Tangential velocity: -the velocity directed tangent to the circle is called tangential or linearvelocity.95. Tangential acceleration: -the acceleration produced when there is change in magnitude ofthe velocity during circular motion.96. Centripetal acceleration: -it is the acceleration directed towards the centre of the rotatingbody and is generated when there is change in direction of the velocity.97. Centripetal force: -the force responsible for centripetal acceleration acts along the string orrope towards the centre.98. Time period of revolution: -the time required by a body to complete one revolution is calledits time period of revolution.Chapter 5Torque, Angular momentum and Equilibrium.(The difficult work of life is to maintain equilibrium in life by hard work inlife)99. Torque: - the turning effect of force is called torque OR the cross product of position vectorand the force applied.100. Moment of a couple: -couple is a pair of forces with equal magnitude and oppositedirection, with lines of action that are parallel but don not coincides.Physics Definitions: 8 Dr. Sajid Ali Talpur
9. 9. 101. Centre of mass: -it is the point on object where the entire mass of the body isconcentrated.102. Centre of gravity: -it is the point where the net gravitational force acts. OR That point in abody or system around which its mass or weight is evenly distributed or balanced andthrough which the gravity acts.103. Equilibrium: -a body at rest or with uniform motion is said to be in equilibrium.104. Static equilibrium: -when a body is at rest it is said to be in static equilibrium.105. Dynamic equilibrium: -a body moving with uniform motion constitutes dynamicequilibrium.106. Translational equilibrium: -when a body moves constant linear velocity it results intranslational equilibrium.107. Rotational equilibrium: -a type of equilibrium in which body rotates in a circle withuniform angular velocity.108. first condition of equilibrium: -according to it “a body will be in equilibrium if the sumof all the forces acting on it is zero”109. second condition of equilibrium: - according to second condition of equilibrium “thebody will be in equilibrium if the sum of all the torques acting on the system or body iszero”110. Angular momentum: -angular momentum may be defined as the cross product of positionvector and linear momentum. i.e. L = r ×pChapter 6GRAVITATION(The planet earth is not perpetual to provide houses to keep alive to you itdigs graves for you too because the same farmer who sows, reaps too; thesame Almighty Allah who sprouts life determines death too not to perish youbut to put perpetual life of heaven or hell in you)111. Gravitation: - it is the natural force of attraction between the material bodies.112. Gravitational field: - it is the around an object under which the effect of gravitation con beexperienced.113. Newton’s law of gravitation: it states that “ every body in the universe attracts every otherbody in the universe with a force of attraction (gravitation) that is directly proportional toPhysics Definitions: 9 Dr. Sajid Ali Talpur
10. 10. the product of their masses and inversely proportional to the square of the distance betweenthem”114. Density: -mass per unit volume is called density.115. Weight: - it is a force through which the earth attracts the bodies towards its centre iscalled weight of the body. W=mg116. Weightlessness: -a condition of free fall OR it is a condition in which body does notexperience ( feel) the gravitational effect.117. Artificial gravity: -a simulated gravity established in space by technological means suchas spinning of the satellite etc.Chapter 7WORK, POWER AND ENERGY(If your small brain can dream big to understand Physics, then why can you bigbody not do small work to let it come true…?)118. Work: -work is said to be done on a body if it attains some displacement with theapplication of force. OR it is the dot product of the applied force and the displacementcovered.119. Conservative field: -A field is said to be conservative if work done is independent of thepath followed and the net work done in a closed path is zero.120. Power: -the rate of doing work is called power. OR work done per unit time.121. Energy: -the ability or capacity to do work is called energy.122. Kinetic energy: -the energy possessed by a body when it is in motion is called kineticenergy.123. Potential energy: - the energy possessed by a body when it is at rest or hanged or due itsposition is called potential energy.124. law of conservation of energy: it states that “ the energy can neither be created nordestroyed”125. Wind: -the moving air is called wind.126. Solar energy: -the energy of the sun light is called solar energy.Physics Definitions: 10 Dr. Sajid Ali Talpur
11. 11. 127. Fossils: - the remains of the organism of the past that owing to some devastations gotburied.Chapter 8WAVE MOTION AND SOUND(WAVES ALREADY EXISTED, WE ONLY DISCOVERED THEM ANDSUBSEQUENTLY GOT MOBILES; THE GOODNESS IS ALREADY EXISTED INPEOPLE WE ONLY NEED TO DISCOVER IT TO GET LOVING LIVES)128. Vibrational motion: -when a body moves to and fro about its mean position it is said to bein vibrational or oscillatory motion129. Periodic motion: -that motion that repeats by itself is called periodic motion.130. Vibration: -one complete round trip of a body about its mean position is called vibration.131. Frequency: -the number of vibrations (or revolutions) per unit time is called frequency.132. Amplitude: -it is the maximum displacement of a vibrating body from the mean position.133. simple harmonic motion: it is characterized by;I. its motion is vibratoryII. acceleration of the body is directly proportional to the displacement about a fixed point atthe middle(mean position)III. The motion of the body is always directed towards the mean position.134. Simple pendulum: -a simple ideal pendulum consists of a point mass suspended with thehelp of a weightless, inextensible and flexible string whose other end is attached with therigid body.135. Time period: -time taken by a body to complete one vibration is called its time period ofvibration.136. Natural time period: -the time period with witch a body vibrates in the absence ofexternal forces.137. Natural frequency: -the frequency at which a system vibrates freely without beingdisturbed by an external force.138. Second’s pendulum: -it is the pendulum whose time period is two seconds.Physics Definitions: 11 Dr. Sajid Ali Talpur
12. 12. 139. Resonance: - when natural frequency of a body capable of vibrating matches with thefrequency of an external periodic force then the body starts vibrating with the increasedamplitudes. The phenomenon is called resonance.140. Wave: - A wave is a traveling disturbance. OR a wave is a mechanism through witchenergy or disturbance travels from one place to the other.141. Mechanical wave: - The wave that requires a material medium (solid, liquid or gas) for itspropagation is called mechanical wave.142. Electromagnetic wave: - the waves that don not require material medium for theirpropagation are called electromagnetic waves.143. Transverse waves: - the waves whose vibrations are perpendicular to the direction of thepropagation of the waves.144. Longitudinal or compressional waves: - a wave in witch vibrations are parallel to thedirection in which a wave is traveling, is called longitudinal (or compressional) wave.145. Frequency of waves: -the number of waves passing through a point in one second is calledfrequency of waves.146. Wave length: -it is the distance between two consecutive (side by side ) crests or troughs.But in case of longitudinal waves it is distance between two successive compressions orrarefactions.147. Sound: - sound is a form of energy that produces the sense of hearing. OR sound is a formof energy that produces sense of hearing in our auditory system.148. Audible sound: -the sound that can be heard and it is of the frequency ranging between 20Hz to 20,000 Hz.149. Infrasonic waves: -sound waves of frequency less than 20 Hz are called infrasonic waves.150. Ultrasonic waves: -The sound waves whose frequency is greater than 20,000 Hz are calledultrasonic waves.151. Music: -the sound that produces pleasant effect in our auditory system is called music.152. Noise: - the sound that has a random, jarring or disagreeable impact on our auditorysystem.153. Intensity of sound: -the amount of sound energy passing perpendicularly through the unitarea of a surface in one second is called intensity of the sound.154. Loudness: -the magnitude of sound produced in our auditory system is called loudness ORthe attribute of sound that determines the magnitude of the auditory sensation produced andthat primarily depends upon the amplitude of the sound waves involved.Physics Definitions: 12 Dr. Sajid Ali Talpur
13. 13. 155. Weber-fechner law: according to it: “the loudness of sound is directly proportional to thelog of intensity of the sound.156. Intensity level: -the difference in the loudness of a given sound and the faintest sound iscalled intensity level.157. Faintest sound: -the threshold sound before below it we can not hear.158. Pitch of sound: -pith is that characteristics of sound with the help of witch a shrill soundcan be distinguished from a grave one.159. Quality: -quality of sound is characteristics of sound with helps distinguishing the soundhaving same pitch and frequency.160. Beats: - To strike repeatedly. OR The pulsation resulting from a combination of two wavesof slightly different frequency161. Adiabatic process: - the thermodynamic process involving no loss or gain of energy in thesystem or particular region.162. Isothermal process: -the thermodynamic process during which the temperature of thesystem remains constant is called isothermal process.163. Doppler’s effect: -the apparent change in pitch of the sound due to the relative motion ofthe source and listener is called Doppler’s effect.164. Sonic boom: -an explosive sound caused by the shock waves preceding an aircrafttraveling at or above the speed of the sound.165. principle of superposition of waves: - according to it: “when particles of a medium aredisturbed simultaneously by two or more waves then their net displacement from theirmean position will be equal to the algebraic sum of the individual displacements due toindividual displacements”166. Standing or stationary waves: - standing wave also called stationary wave is thecombination of two waves moving in opposite direction, each with same amplitude andenergy and is generated when the string is confined at both the sides and then vibrated.167. Antinodes: -the points where the vibrating displacement is maximum from the centre.168. Node: -the points of zero amplitude are called nodes.169. fundamental frequency: - also called first harmonic is the lowest tone of harmonic series170. overtone: -if the string tuned properly such that two loops are formed then the frequency f2with which now it vibrates first overtone or second harmonic171. Sonometer: - standing waves generating device.Physics Definitions: 13 Dr. Sajid Ali Talpur
14. 14. 172. Loop: -the more or less circular figure that curves back to cross itself.Chapter 9THE NATURE OF LIGHT(Constructive interference i.e. the brightness results when the uniting wavesare in phase but it leads it destructive interference when they are out ofphase, so stay united to make happier life days by these ways)173. LIGHT: - THE NATURAL AGENT THAT STIMULATES SIGHT AND MAKESTHINGS VISIBLE.174. Interference of waves: -if two exactly similar waves superpose each other (i.e. passthrough the same region of space simultaneously) then at some points they reinforce (i.e.they help each other and their effect enhances) while at other points they cancel eachother’s effect (i.e. their net effect decreases. This phenomenon is known as interference oflight.175. Phase coherence: -if the waves produced simultaneously are alike, they are said to be inphase coherence.176. Constructive interference: -constructive interference takes place when the wavesreinforce each other.177. Destructive interference: - it is brought about when the waves cancel each other’s effect.178. Path difference: -it is the distance covered by waves measured from source to the givenpoint.179. Fringe spacing: -it is the distance between two consecutive bright or dark fringes.180. Phase reversal: - when a wave traveling in a rare medium (medium of lower refractiveindex) reflects from a denser medium of high refractive index, then its crest beforereflection becomes trough after reflection.181. Newton’s rings: - if a beam of monochromatic light is allowed to fall on a Plano-convexlens placed on a plane glass plate then alternate bright and dark rings are produced. Theserings are known as Newton’s rings.182. Diffraction:-the bending of light around the edges of an object. OR The breaking up of aray of light bands or into the colors of the spectrum, caused by the interference of one partPhysics Definitions: 14 Dr. Sajid Ali Talpur
15. 15. of beam with another, as when the ray is deflected at the edge of an opaque object or passesthrough a narrow slit.183. Frensel diffraction: in Frensel diffraction the source and the screen are finite and thediffracted rays are not parallel.184. Frawnhoffer diffraction: -in Frawnhoffer diffraction the point source of light and thescreen on witch the diffraction is to be produced are at infinite distance so that thediffracted rays become parallel.185. Diffraction grating: - a plate of glass or metal ruled with very close parallel lines,producing spectrum by interference or diffraction of light.186. Grating element: -let a be the width of a slit and b be the width of an opaque then a + b iscalled grating element.187. Path difference: -the difference in the optical paths of two light rays having commoninitial and final points. OR An X-ray beam is reflected from the upper plane and the secondx-ray is reflected from the lower plane these two beams will cover different distancesbefore entering the eye (second beam will cover longer distance) difference in distancecovered is called path difference.188. Wave fronts: - the geometrical pattern (or locus of all points), having same state ofvibration is known as wave front.189. Polarization of light: -the phenomenon of confining the vibrations of electric vectors inonly one plane, ultimately leading to the proof of light waves as transverse.Chapter 10Geometrical Optics(People are bad enough to tease you but I am sure you are good enough toforgive them)190. Optics: -the scientific study of light and vision, chiefly the generation, propagation anddetection of electromagnetic radiation, having wavelength greater than that of x-ray andsmaller than that of microwaves.191. Reflection: - the bouncing back of light into the same medium is called reflection.192. laws of reflection:I. Angle of incidence is always equal to the angle of reflection.Physics Definitions: 15 Dr. Sajid Ali Talpur
16. 16. II. Incident ray, refracted ray and the normal to the reflecting surface, all are in oneplane.193. regular reflection: - in such reflection the incident and the reflected rays both are parallel194. Diffused or irregular reflection: -if the incident and the reflected both the rays are notparallel to each other they are said to form diffused or irregular reflection.195. Mirror: - the reflecting surfaces are called mirrors.196. Lens: -the refracting objects are known as lenses.197. Real image: -an image that can be projected at screen, is inverted and formed by the actualintersection of the reflected or refracted rays.198. Virtual image: -An image that can not be projected at screen, is erect and formed by thediverging reflected or refracted rays when they are produced backward.199. Spherical mirrors: -spherical mirror is a part of a sphere.200. Concave mirror: - if the reflecting surface is on the inner side of the spherical mirror thenit is known as a concave mirror.201. Convex mirror: -if the reflecting surface is on the outer side of the spherical mirror then itis known as convex mirror.202. Pole: - the mid point of a spherical mirror or lens is called pole.203. Curvature: -the state of being curved or the degree to which some thing is curved.204. Centre of curvature: -centre of the sphere of which the spherical mirror or lens is a part iscalled centre of curvature.205. Radius of curvature: -radius of sphere of which the mirror or lens is a part is called radiusof curvature.206. Principle axis: -an imaginary straight line passing through pole and centre of curvature ofa mirror or lens is called principle axis.207. Focus of a concave mirror: -if a beam of rays parallel to principle axis is incident upon aconcave mirror then after reflection from the mirror all the rays converge to one point “F”.this is called focus.208. Focus of a convex mirror: -if a beam of rays parallel to principle axis is incident uponconvex mirror then after reflection from the mirror all the rays diverge and appear to comefrom a point behind the mirror. The point is called focus of the convex mirror.Physics Definitions: 16 Dr. Sajid Ali Talpur
17. 17. 209. Principle focus of the convex lens: -the converging point of refracted rays from theconvex lens.210. Focal length: -the distance between focus and pole of a mirror is called its focal length.211. Mirror equation: -mirror equation is mathematical relation between object distance p,image distance q and the focal length f of a mirror.212. Magnification: -the ratio of image height to object height. It may also be defined as theratio of image distance to object distance.213. Angular magnification: -angular magnification is the ratio of visual angle subtended byan image to the visual angle subtended by the object.214. Refraction: -the passage of light, sound, heat etc from one medium to another with theoblique change in the direction.215. Snell’s law: according it: “the ratio of sine of angle of incidence to sine of angle ofrefraction for a given pair of media is always constant”216. refractive index: - it may be defined in the following ways:I. The ratio of speed of light in medium 1 to the speed of light in medium 2II. The ratio of incident angle to that refracted angle.III. The ratio of real depth to apparent depth.IV. Reciprocal to the sine of critical angle217. Critical angle: -the angle of incidence for which angle of refraction is equal to 90 is calledcritical angle.218. Total internal reflection: -if the angle of incidence is increased beyond the critical anglethen no refraction will take place, instead light will be totally reflected back. Thephenomenon is called total internal reflection.219. Convex lens: -the converging lenses thicker at the middle and thinner at the edges arecalled convex lenses.220. Concave lens: the diverging lens thinner at the middle and thicker at the edges.221. Aperture: -the diameter of boundary of a lens is called aperture.222. Power of a lens: -the reciprocal of focal length expressed in diopters.223. Spherical aberration: -the failure in of refracted rays in converging at the principle focusultimately resulting in the blurring of the image.224. Chromatic aberration: -color distortion in an image produced by a lens, caused by theinability of the lens to bring the various colors of light to focus at a single point.Physics Definitions: 17 Dr. Sajid Ali Talpur
18. 18. 225. Microscope: -an instrument with the help of which the minute objects can be seenmagnified.226. least distance of distinct vision: -the nearest position to which the object can be seenclearly without stressing the eyes227. Compound microscope: -it is an optical instrument used to see near objects of very smalldimensions clearly, primarily consist of objective lens and eye piece.228. Objective lens in compound microscope: -the convex lens of short focal length, nearer toobject is called objective lens.229. Eye piece (ocular lens) of compound microscope: - the convex lens of relatively largerfocal, near to eye to display the image.230. Telescope: -telescope is an optical instrument used to make distinct objects appearmagnified, so that they may be seen distinctly.231. Astronomical telescope: -it is an optical instrument that is used to view heavenly bodies(i.e. planets, stars etc.)232. Terrestrial telescope: -it is an optical instrument used to view distinct objects on earthclearly.233. Galilean telescope: -also called opera glass is used to view objects on earth.234. Spectrometer: -an apparatus used for the recording and measuring spectra, especially as amethod of analysis.235. The eye: -the light sensitive vision organ.236. Sclera: -the tough white fibrous outer envelope of tissue, covering the entire eye ballexcept cornea.237. Cornea: -the transparent convex shaped front tissue, covering iris and pupil.238. Choroids: -the pigmented vascular layer of the eyeball, lying between sclera and retina.239. Iris: -the contractile, circular diaphragm forming the colored portion of the eye andcontaining a circular opening, the pupil, in its center.240. Pupil: -the opening in the center of the iris through which light enters the eye.241. Retina: -a layer at the back of eyeball, containing cells that are sensitive to light and thattrigger nerve impulses that pass via the optic nerve to the brain.242. Crystalline lens: -the transparent elastic structure behind the iris by which light is focusedonto the retina.Physics Definitions: 18 Dr. Sajid Ali Talpur
19. 19. 243. Aqueous humour: -the clear watery fluid, circulating in the chamber of the eye betweenthe cornea and lens.244. Vitreous humour: -the transparent gelatinous substance, filling the eye ball behind thecrystalline lens.245. Myopia: -it is the condition of short sightedness in which nearby objects can be seenclearly.246. Hyperopia: - an abnormal condition in which the distinct objects can be seen clearly ratherthan near one.Note: Chemistry and Biology Definitions also available!e.g.247. Chemistry: - The scientific study of inanimate matter is called Chemistry.248. Biology: - The scientific study of life is called biology249. Ornithology: -The scientific study of birds is called ornithology.250. Gerontology: -The science of aging is called gerontology.By the same Author: Success tips Chemistry definitionsPhysics Definitions: 19 Dr. Sajid Ali Talpur
20. 20.  Definitions and MCQs on branches of Biology Ninth Class Chemistry MCQs Ninth Class Biology MCQs Scientific Biological Reasons Definitions, Scientific Reasons and MCQs on Chemistry Skeletal muscles Physiology BCQs Biology MCQs test for entry test Chemistry MCQs test for entry test Cardiovascular system anatomy quiz Lower limb Anatomy MCQs How to achieve heaven? The mechanism of goodness and badness. Spiritual successful life quotations Love the Prophet Muhammad (s.a.w) Quotations on the Prophet Muhammad (s.a.w) Endocrinology – Hormone MCQsPhysics Definitions: 20 Dr. Sajid Ali Talpur
21. 21. Physics Definitions: 21 Dr. Sajid Ali Talpur