1. The document discusses electric current and resistance. It defines current as the rate of flow of electric charge and explains that current can be direct or alternating.
2. It describes how current flows in different materials, with free electrons causing current in metals. It introduces concepts like current density, drift velocity, and mobility.
3. Ohm's law is explained, which relates current, voltage, and resistance. The factors that determine a conductor's resistance are described.
My Favourite Scientists - Albert Einstein & APJ Abdul Kalammeeravettoor
This document provides an overview of Albert Einstein's life and career accomplishments from his birth in 1879 to his death in 1955. Some key points:
- Einstein was born in Germany and showed an early interest in science after being impressed by a compass as a young boy. He had difficulties with exams but developed his Special Theory of Relativity in 1905 while working as a patent clerk.
- In 1915, Einstein completed his General Theory of Relativity which proposed gravity as the warping of space-time. This was proven correct by an eclipse observation in 1919, making Einstein an overnight celebrity.
- Throughout his life, Einstein published groundbreaking papers on many topics in physics and won the Nobel Prize in 1921. He imm
An electric dipole is formed by two equal and opposite charges separated by a small distance. Many molecules have their positive and negative centers of charge in different locations, causing them to behave as permanent electric dipoles like CO, H2O, NH3, and HCl. The electric dipole moment vector points from the negative charge to the positive charge and its magnitude is calculated as the product of one of the charges and the distance between them. Water molecules have a permanent electric dipole moment due to the separation of positive hydrogen atoms and the negative oxygen atom.
1) The document discusses common student misconceptions about the particulate nature of matter, including that matter is made of continuous substances rather than discrete particles with empty space between them, and that particles in solids do not move.
2) It provides examples of misconceptions students have when explaining processes like a balloon deflating or a perfume spreading, and suggests teaching strategies like analogies and examples to help students understand the concept of particles in random motion.
3) Suggestions for teaching include using metaphors to make particle motion more intuitive, providing clear examples for students to observe particle diffusion, and allowing group discussions to build on students' existing ideas.
This document discusses three effects of electricity: thermal, chemical, and thermoelectric. The thermal effect explains how an electric current produces heat due to the collision of electrons with atoms in a conductor. Joule's law quantifies this relationship. The chemical effect discusses electrolysis and Faraday's laws of electrolysis. Electrolysis is the process of using a direct current to cause a non-spontaneous chemical reaction. The thermoelectric effect explains how a temperature difference across junctions of two different conductors can produce an electric current, as described by Seebeck's discovery of the thermoelectric effect. Key concepts covered include Seebeck series, neutral temperature, and temperature of inversion.
The document summarizes key concepts related to electric current, current density, and magnetostatics. It defines:
- Electric current as the rate of charge transfer through a surface. The SI unit is the ampere.
- Conventional current direction versus actual electron flow direction in conductors.
- Current density as the current per unit area, with units of amperes per square meter. It is proportional to and in the same direction as the electric field in a conductor based on Ohm's law.
- Surface and volume current density and how they relate to the Biot-Savart law for calculating magnetic fields.
This document provides instructions for navigating a presentation on physics concepts. It outlines how to view the presentation as a slideshow and advance through it. The table of contents lists four sections that cover changes in motion, Newton's laws of motion, everyday forces, and sample problems. Force diagrams and free-body diagrams are used to represent forces acting on objects. Newton's three laws of motion relate forces, mass, and acceleration. Friction and normal forces are types of contact forces that oppose motion.
7.1 Atomic, nuclear and particle physicsPaula Mills
This document discusses atomic, nuclear and particle physics concepts including:
- Atomic energy levels and line spectra which provide evidence that electrons can only have certain discrete energy values within an atom.
- The Bohr model of the atom which assumed quantized electron energy levels and explained hydrogen atom spectra.
- Nuclear structure including mass number, nucleons, atomic number, isotopes, and interactions within the nucleus.
- Three types of nuclear radiation - alpha, beta, and gamma rays - and how they differ in their ionizing properties and penetration abilities due to their mass and charge.
- Nuclear stability and how heavier nuclei require more neutrons to counter the repulsive force between protons.
- Two
My Favourite Scientists - Albert Einstein & APJ Abdul Kalammeeravettoor
This document provides an overview of Albert Einstein's life and career accomplishments from his birth in 1879 to his death in 1955. Some key points:
- Einstein was born in Germany and showed an early interest in science after being impressed by a compass as a young boy. He had difficulties with exams but developed his Special Theory of Relativity in 1905 while working as a patent clerk.
- In 1915, Einstein completed his General Theory of Relativity which proposed gravity as the warping of space-time. This was proven correct by an eclipse observation in 1919, making Einstein an overnight celebrity.
- Throughout his life, Einstein published groundbreaking papers on many topics in physics and won the Nobel Prize in 1921. He imm
An electric dipole is formed by two equal and opposite charges separated by a small distance. Many molecules have their positive and negative centers of charge in different locations, causing them to behave as permanent electric dipoles like CO, H2O, NH3, and HCl. The electric dipole moment vector points from the negative charge to the positive charge and its magnitude is calculated as the product of one of the charges and the distance between them. Water molecules have a permanent electric dipole moment due to the separation of positive hydrogen atoms and the negative oxygen atom.
1) The document discusses common student misconceptions about the particulate nature of matter, including that matter is made of continuous substances rather than discrete particles with empty space between them, and that particles in solids do not move.
2) It provides examples of misconceptions students have when explaining processes like a balloon deflating or a perfume spreading, and suggests teaching strategies like analogies and examples to help students understand the concept of particles in random motion.
3) Suggestions for teaching include using metaphors to make particle motion more intuitive, providing clear examples for students to observe particle diffusion, and allowing group discussions to build on students' existing ideas.
This document discusses three effects of electricity: thermal, chemical, and thermoelectric. The thermal effect explains how an electric current produces heat due to the collision of electrons with atoms in a conductor. Joule's law quantifies this relationship. The chemical effect discusses electrolysis and Faraday's laws of electrolysis. Electrolysis is the process of using a direct current to cause a non-spontaneous chemical reaction. The thermoelectric effect explains how a temperature difference across junctions of two different conductors can produce an electric current, as described by Seebeck's discovery of the thermoelectric effect. Key concepts covered include Seebeck series, neutral temperature, and temperature of inversion.
The document summarizes key concepts related to electric current, current density, and magnetostatics. It defines:
- Electric current as the rate of charge transfer through a surface. The SI unit is the ampere.
- Conventional current direction versus actual electron flow direction in conductors.
- Current density as the current per unit area, with units of amperes per square meter. It is proportional to and in the same direction as the electric field in a conductor based on Ohm's law.
- Surface and volume current density and how they relate to the Biot-Savart law for calculating magnetic fields.
This document provides instructions for navigating a presentation on physics concepts. It outlines how to view the presentation as a slideshow and advance through it. The table of contents lists four sections that cover changes in motion, Newton's laws of motion, everyday forces, and sample problems. Force diagrams and free-body diagrams are used to represent forces acting on objects. Newton's three laws of motion relate forces, mass, and acceleration. Friction and normal forces are types of contact forces that oppose motion.
7.1 Atomic, nuclear and particle physicsPaula Mills
This document discusses atomic, nuclear and particle physics concepts including:
- Atomic energy levels and line spectra which provide evidence that electrons can only have certain discrete energy values within an atom.
- The Bohr model of the atom which assumed quantized electron energy levels and explained hydrogen atom spectra.
- Nuclear structure including mass number, nucleons, atomic number, isotopes, and interactions within the nucleus.
- Three types of nuclear radiation - alpha, beta, and gamma rays - and how they differ in their ionizing properties and penetration abilities due to their mass and charge.
- Nuclear stability and how heavier nuclei require more neutrons to counter the repulsive force between protons.
- Two
- Electric charge is quantized and can only exist in integer multiples of the elementary charge of electrons and protons. Charge is conserved in nuclear decay processes.
- Coulomb's law describes the electric force between two point charges. The electric field is defined as the force per unit charge exerted on a test charge. Gauss's law relates the net electric flux through a closed surface to the enclosed charge.
- The electric field due to symmetric charge distributions like point charges, spherical charge distributions, and charged plates can be calculated using Gauss's law. This allows determining electric fields without calculating the contributions of individual charges.
Class 12th physics current electricity ppt Arpit Meena
1. The document discusses key concepts related to electric current including definitions of current and conventional current, drift velocity, current density, Ohm's law, resistance, resistivity, conductance, conductivity, and temperature dependence of resistance.
2. It also covers color codes for carbon resistors, series and parallel combinations of resistors, definitions of emf and internal resistance of cells, and series and parallel combinations of cells.
3. The document provides formulas and explanations for many important electrical concepts in a comprehensive yet concise manner.
Structure of Atoms some basic concepts of atomic structure its history of modelling and also the present and accepted model including the quantum model of atomic structure.
Classification of elements, unit iii class 11Arvindchauhan23
The document discusses the periodic classification of elements. It begins with a brief history of the periodic table, from Dobereiner's discovery of triads in 1817 to Moseley's modern periodic law in 1942 based on atomic number. Mendeleev arranged the elements into the first periodic table in 1869 based on atomic weight and properties, and was able to predict new elements. The modern periodic table is arranged by atomic number into rows and columns, with inner transition metals and lanthanides/actinides in separate sections. Electronic configuration explains the placement and properties of elements in the periodic table.
Free body diagrams show the relative magnitude and direction of all forces acting upon an object by isolating it from its surroundings. The document provides examples of free body diagrams for the Statue of Liberty, a sitting gorilla, a wooden swing, a bungee jumper's bucket, a traffic light, and the pin at point A of a truss bridge. Forces are shown as vectors with arrows indicating direction and labels providing magnitudes. Diagrams for static systems will sum the vertical and horizontal forces to zero, indicating equilibrium.
1) Electric charge is a fundamental property of matter that comes in two types: positive and negative. Like charges repel and unlike charges attract, as described by Coulomb's Law.
2) An electric field is a physical quantity that permeates space and is created by electric charges. It exerts force on other charges and is a vector field. The electric field is proportional to the charge creating it and inversely proportional to the distance from that charge.
3) When multiple charges are present, the net electric field is the vector sum of the individual electric fields according to the superposition principle. Electric field lines provide a pictorial representation of electric fields, with density and direction corresponding to field strength and direction.
This document discusses intermolecular forces and the behavior of gases. It describes three types of intermolecular forces - London dispersion forces, dipole-dipole forces, and dipole-induced dipole forces. It also explains the gas laws of Boyle, Charles, Gay-Lussac, Avogadro, Dalton and the ideal gas equation. Real gases deviate from ideal behavior at high pressures due to molecular interactions. The van der Waals equation accounts for these interactions through correction terms.
Coulomb's law describes the electrostatic force between two point charges. The magnitude of the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. An electric field is a region of space where an electric charge will experience a force, with field lines pointing away from positive charges and toward negative charges. The magnitude of the electric field can be calculated as the force exerted on a test charge divided by the charge, with units of newtons per coulomb.
Electric flux is defined as the number of electric field lines passing through a given surface area. It is a scalar quantity measured in newton meters squared per coulomb. The electric flux through a surface depends on both the electric field strength and the orientation of the surface relative to the field lines. For a uniform electric field, the flux is greatest when the surface is perpendicular to the field lines and zero when parallel. For non-uniform fields, the surface is divided into small elements and the flux is calculated over each then summed.
Gravitation has been the most common phenomenon in our lives but somewhere down the line we don't know musch about it. So here is a presentation whic will help you out to know what it is !! I'll be makin it available for download once i submit it in school :P :P ! Coz last one of the brats showed the same presentation that i uploade and unfortunatele his roll number fell before mine ! I was damned..:D :D :P
- An equipotential surface is a surface where all points have the same electric potential. For a point charge, equipotential surfaces are concentric spherical surfaces. For a uniform electric field, equipotential surfaces form planes perpendicular to the field.
- The electric field is always perpendicular to equipotential surfaces. If it is not, work would be required to move a charge along the surface, contradicting the definition.
- Electrostatic potential energy of a system of point charges depends only on the distances between charges. It is equal to the work required to assemble the charges from infinity.
The document describes projectile motion and the key concepts involved. It defines a projectile as a particle thrown obliquely near the earth's surface that moves along a curved path. It discusses the trajectory, components of velocity and acceleration, equations of motion, time of flight, range, maximum height, and velocity of a projectile at any instant. Examples of projectile motion calculations are provided to illustrate how to determine initial velocities, maximum height, range, and the time and distance required for a bomb to hit a target from an airplane.
Chemical kinetics deals with the study of reaction rates and their mechanisms. The rate of a reaction depends on factors like concentration, temperature, pressure, and presence of a catalyst. Rate laws relate the rate of reaction to the concentrations of reactants. The rate law is determined experimentally and cannot be predicted from the balanced chemical equation alone. Integrated rate laws allow determination of reaction order based on plots of concentration versus time data. Half-life is the time required for a reactant's concentration to reduce to half of its initial value and can be used to characterize reaction order.
1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
1. The document discusses electric fields created by point charges and electric dipoles. It defines electric field strength and describes how electric field strength is calculated for point charges and dipoles.
2. Key properties of electric field lines are outlined, including that they emanate from positive charges and terminate at negative charges.
3. Formulas are given for calculating the torque and work done on an electric dipole placed in a uniform electric field. The dipole will experience a torque causing it to rotate into alignment with the field.
Albert Einstein was born in Germany in 1879 and went on to become one of the most influential physicists of the 20th century. In his "miracle year" of 1905, he published four groundbreaking papers, including his special theory of relativity containing his famous equation E=mc2. He was awarded the Nobel Prize in Physics in 1921 for his services to theoretical physics. Later in life, Einstein immigrated to the United States and took a position at the Institute for Advanced Study in Princeton, New Jersey. He died in 1955 at the age of 76.
1) Projectile motion involves both horizontal and vertical motion that occur independently. A projectile is an object thrown with an initial velocity that is affected by gravity during flight.
2) The path of a projectile is parabolic. Key elements include maximum height, time of flight, and horizontal range.
3) For an object projected at an angle, its motion can be analyzed as two independent motions - horizontal and vertical. The path remains parabolic and factors like initial velocity and launch angle affect maximum height and horizontal range.
Dev Gupta presents on Kirchoff's Current Law (KCL). KCL states that the total current entering any node in an electrical circuit must equal the total current leaving that node. It is based on the principle of conservation of charge, which states that electrical charge can neither be created nor destroyed. The presentation provides examples of using KCL to solve for unknown currents in various circuit problems. It concludes by offering to answer any questions and providing a link to download the presentation slides.
The document discusses electric fields and electric dipoles. It defines the electric field as a vector field generated by electric charges that acts upon other charges. Electric field lines are introduced to visualize electric fields, with higher density of lines indicating stronger fields. Dipoles, such as water molecules, have a built-in electric polarity due to unequal charge distribution. When placed in an external electric field, dipoles experience a torque attempting to align them with the field but do not experience a net force. Microwave ovens work by using an oscillating electric field to cause the rotation of polar water molecules in food, generating heat through molecular collisions.
1. Cells connected in series have their emfs add up but their currents remain equal. Cells in parallel have the same emf but their currents divide.
2. The internal resistance of cells in series adds up while the reciprocal of the internal resistance adds up for parallel cells.
3. A mixed grouping of cells has some cells in series forming rows, and the rows in parallel. The total resistance is minimized when the rows' resistance equals the series resistance within rows.
Chap 11 - ELECTRIC CURRENT THROUGH CONDUCTOR.pptxPooja M
This document discusses electric current through conductors. It begins by defining electric current as the rate of flow of electric charge. In metallic conductors like wires, electric current is carried by the flow of electrons. When a large number of metal atoms come together, their valence electrons become delocalized and free to move throughout the material as conduction electrons.
When a potential difference is applied across a conductor, the conduction electrons begin to drift in the direction of the applied electric field at a constant drift speed. This drift of electrons constitutes an electric current. Ohm's law establishes the direct proportional relationship between current and applied potential difference for many materials when their physical state remains unchanged. The proportionality constant is the resistance of the material.
Electric current is defined as the flow of electric charge. It is measured in amperes (A), which is equal to one coulomb of charge passing through an area in one second. Current can be direct, where the direction of flow is constant, or alternating, where the direction and magnitude continuously changes. Resistance is a material property that impedes current flow and is measured in ohms. Ohm's law states that current is directly proportional to voltage and inversely proportional to resistance.
- Electric charge is quantized and can only exist in integer multiples of the elementary charge of electrons and protons. Charge is conserved in nuclear decay processes.
- Coulomb's law describes the electric force between two point charges. The electric field is defined as the force per unit charge exerted on a test charge. Gauss's law relates the net electric flux through a closed surface to the enclosed charge.
- The electric field due to symmetric charge distributions like point charges, spherical charge distributions, and charged plates can be calculated using Gauss's law. This allows determining electric fields without calculating the contributions of individual charges.
Class 12th physics current electricity ppt Arpit Meena
1. The document discusses key concepts related to electric current including definitions of current and conventional current, drift velocity, current density, Ohm's law, resistance, resistivity, conductance, conductivity, and temperature dependence of resistance.
2. It also covers color codes for carbon resistors, series and parallel combinations of resistors, definitions of emf and internal resistance of cells, and series and parallel combinations of cells.
3. The document provides formulas and explanations for many important electrical concepts in a comprehensive yet concise manner.
Structure of Atoms some basic concepts of atomic structure its history of modelling and also the present and accepted model including the quantum model of atomic structure.
Classification of elements, unit iii class 11Arvindchauhan23
The document discusses the periodic classification of elements. It begins with a brief history of the periodic table, from Dobereiner's discovery of triads in 1817 to Moseley's modern periodic law in 1942 based on atomic number. Mendeleev arranged the elements into the first periodic table in 1869 based on atomic weight and properties, and was able to predict new elements. The modern periodic table is arranged by atomic number into rows and columns, with inner transition metals and lanthanides/actinides in separate sections. Electronic configuration explains the placement and properties of elements in the periodic table.
Free body diagrams show the relative magnitude and direction of all forces acting upon an object by isolating it from its surroundings. The document provides examples of free body diagrams for the Statue of Liberty, a sitting gorilla, a wooden swing, a bungee jumper's bucket, a traffic light, and the pin at point A of a truss bridge. Forces are shown as vectors with arrows indicating direction and labels providing magnitudes. Diagrams for static systems will sum the vertical and horizontal forces to zero, indicating equilibrium.
1) Electric charge is a fundamental property of matter that comes in two types: positive and negative. Like charges repel and unlike charges attract, as described by Coulomb's Law.
2) An electric field is a physical quantity that permeates space and is created by electric charges. It exerts force on other charges and is a vector field. The electric field is proportional to the charge creating it and inversely proportional to the distance from that charge.
3) When multiple charges are present, the net electric field is the vector sum of the individual electric fields according to the superposition principle. Electric field lines provide a pictorial representation of electric fields, with density and direction corresponding to field strength and direction.
This document discusses intermolecular forces and the behavior of gases. It describes three types of intermolecular forces - London dispersion forces, dipole-dipole forces, and dipole-induced dipole forces. It also explains the gas laws of Boyle, Charles, Gay-Lussac, Avogadro, Dalton and the ideal gas equation. Real gases deviate from ideal behavior at high pressures due to molecular interactions. The van der Waals equation accounts for these interactions through correction terms.
Coulomb's law describes the electrostatic force between two point charges. The magnitude of the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them. An electric field is a region of space where an electric charge will experience a force, with field lines pointing away from positive charges and toward negative charges. The magnitude of the electric field can be calculated as the force exerted on a test charge divided by the charge, with units of newtons per coulomb.
Electric flux is defined as the number of electric field lines passing through a given surface area. It is a scalar quantity measured in newton meters squared per coulomb. The electric flux through a surface depends on both the electric field strength and the orientation of the surface relative to the field lines. For a uniform electric field, the flux is greatest when the surface is perpendicular to the field lines and zero when parallel. For non-uniform fields, the surface is divided into small elements and the flux is calculated over each then summed.
Gravitation has been the most common phenomenon in our lives but somewhere down the line we don't know musch about it. So here is a presentation whic will help you out to know what it is !! I'll be makin it available for download once i submit it in school :P :P ! Coz last one of the brats showed the same presentation that i uploade and unfortunatele his roll number fell before mine ! I was damned..:D :D :P
- An equipotential surface is a surface where all points have the same electric potential. For a point charge, equipotential surfaces are concentric spherical surfaces. For a uniform electric field, equipotential surfaces form planes perpendicular to the field.
- The electric field is always perpendicular to equipotential surfaces. If it is not, work would be required to move a charge along the surface, contradicting the definition.
- Electrostatic potential energy of a system of point charges depends only on the distances between charges. It is equal to the work required to assemble the charges from infinity.
The document describes projectile motion and the key concepts involved. It defines a projectile as a particle thrown obliquely near the earth's surface that moves along a curved path. It discusses the trajectory, components of velocity and acceleration, equations of motion, time of flight, range, maximum height, and velocity of a projectile at any instant. Examples of projectile motion calculations are provided to illustrate how to determine initial velocities, maximum height, range, and the time and distance required for a bomb to hit a target from an airplane.
Chemical kinetics deals with the study of reaction rates and their mechanisms. The rate of a reaction depends on factors like concentration, temperature, pressure, and presence of a catalyst. Rate laws relate the rate of reaction to the concentrations of reactants. The rate law is determined experimentally and cannot be predicted from the balanced chemical equation alone. Integrated rate laws allow determination of reaction order based on plots of concentration versus time data. Half-life is the time required for a reactant's concentration to reduce to half of its initial value and can be used to characterize reaction order.
1) The document provides one mark, two mark and three mark questions from the chapter on Electric Charges and Fields.
2) It includes questions testing definitions of key terms like electric charge, electric field, electric dipole moment, Gauss's law.
3) It also has questions requiring diagrams of electric field patterns and derivations of expressions for force between charges and electric field.
1. The document discusses electric fields created by point charges and electric dipoles. It defines electric field strength and describes how electric field strength is calculated for point charges and dipoles.
2. Key properties of electric field lines are outlined, including that they emanate from positive charges and terminate at negative charges.
3. Formulas are given for calculating the torque and work done on an electric dipole placed in a uniform electric field. The dipole will experience a torque causing it to rotate into alignment with the field.
Albert Einstein was born in Germany in 1879 and went on to become one of the most influential physicists of the 20th century. In his "miracle year" of 1905, he published four groundbreaking papers, including his special theory of relativity containing his famous equation E=mc2. He was awarded the Nobel Prize in Physics in 1921 for his services to theoretical physics. Later in life, Einstein immigrated to the United States and took a position at the Institute for Advanced Study in Princeton, New Jersey. He died in 1955 at the age of 76.
1) Projectile motion involves both horizontal and vertical motion that occur independently. A projectile is an object thrown with an initial velocity that is affected by gravity during flight.
2) The path of a projectile is parabolic. Key elements include maximum height, time of flight, and horizontal range.
3) For an object projected at an angle, its motion can be analyzed as two independent motions - horizontal and vertical. The path remains parabolic and factors like initial velocity and launch angle affect maximum height and horizontal range.
Dev Gupta presents on Kirchoff's Current Law (KCL). KCL states that the total current entering any node in an electrical circuit must equal the total current leaving that node. It is based on the principle of conservation of charge, which states that electrical charge can neither be created nor destroyed. The presentation provides examples of using KCL to solve for unknown currents in various circuit problems. It concludes by offering to answer any questions and providing a link to download the presentation slides.
The document discusses electric fields and electric dipoles. It defines the electric field as a vector field generated by electric charges that acts upon other charges. Electric field lines are introduced to visualize electric fields, with higher density of lines indicating stronger fields. Dipoles, such as water molecules, have a built-in electric polarity due to unequal charge distribution. When placed in an external electric field, dipoles experience a torque attempting to align them with the field but do not experience a net force. Microwave ovens work by using an oscillating electric field to cause the rotation of polar water molecules in food, generating heat through molecular collisions.
1. Cells connected in series have their emfs add up but their currents remain equal. Cells in parallel have the same emf but their currents divide.
2. The internal resistance of cells in series adds up while the reciprocal of the internal resistance adds up for parallel cells.
3. A mixed grouping of cells has some cells in series forming rows, and the rows in parallel. The total resistance is minimized when the rows' resistance equals the series resistance within rows.
Chap 11 - ELECTRIC CURRENT THROUGH CONDUCTOR.pptxPooja M
This document discusses electric current through conductors. It begins by defining electric current as the rate of flow of electric charge. In metallic conductors like wires, electric current is carried by the flow of electrons. When a large number of metal atoms come together, their valence electrons become delocalized and free to move throughout the material as conduction electrons.
When a potential difference is applied across a conductor, the conduction electrons begin to drift in the direction of the applied electric field at a constant drift speed. This drift of electrons constitutes an electric current. Ohm's law establishes the direct proportional relationship between current and applied potential difference for many materials when their physical state remains unchanged. The proportionality constant is the resistance of the material.
Electric current is defined as the flow of electric charge. It is measured in amperes (A), which is equal to one coulomb of charge passing through an area in one second. Current can be direct, where the direction of flow is constant, or alternating, where the direction and magnitude continuously changes. Resistance is a material property that impedes current flow and is measured in ohms. Ohm's law states that current is directly proportional to voltage and inversely proportional to resistance.
The document discusses electric current and related concepts. It defines current as the flow of electric charge from one place to another, measured in amperes. Current can be direct or alternating. Resistance is a property that weakens current flow and is measured in ohms. Ohm's law states current is directly proportional to voltage and inversely proportional to resistance. Kirchhoff's laws govern the analysis of electric circuits.
The document discusses electric current and related concepts. It defines current as the flow of electric charge from one place to another, measured in amperes. Current can be direct or alternating. Resistance is a property that weakens current flow and is measured in ohms. Ohm's law states current is directly proportional to voltage and inversely proportional to resistance. Circuits can have one or more loops and resistors can be connected in series or parallel. Power is the rate at which electrical energy is transferred by a current.
Electric current is defined as the flow of electric charge. It is measured in amperes (A), which is equal to one coulomb of charge passing through an area in one second. Current can be direct, where the direction of flow is constant, or alternating, where the direction and magnitude continuously changes. Resistance is a property that weakens current flow and is measured in ohms. According to Ohm's law, current is directly proportional to voltage and inversely proportional to resistance.
1. The document covers basic electrical concepts including circuits, charge, voltage, current, resistance, Ohm's law, conductors, insulators, semiconductors, and measurement devices.
2. Key concepts discussed include Kirchhoff's current and voltage laws, factors that influence resistance, and applications of electrical concepts like batteries and power supplies.
3. Engineering concepts such as resistivity of materials and its relationship to resistance through geometry are examined alongside historical scientists like Ohm, Ampere, and Volta who contributed to the field.
This document discusses how electric current flows in metallic conductors. It explains that metals contain free electrons that are not bound to any particular nucleus and can move throughout the material. When an electric field is applied, the free electrons drift in the opposite direction of the field, constituting an electric current. Their drift velocity depends on factors like the electric field strength, temperature, and material properties. The document also introduces concepts like relaxation time and how increasing certain variables affects resistance.
This document provides an overview of key concepts in electricity including:
1. Electric current is the flow of electrons through a conductor. Current is measured in amperes and flows from positive to negative terminals.
2. An electric circuit is a closed loop that allows current to flow. A circuit includes a power source, conducting wires, and components like light bulbs.
3. Resistance is a material's opposition to current flow. It is measured in ohms and depends on a material's length, cross-sectional area, and resistivity.
Ph8253 physics for electronics engineeringSindiaIsac
1) The document discusses conducting materials and their properties. It describes how metals have high electrical conductivity due to free electrons. Current density is defined as the current per unit area.
2) Conducting materials are classified as zero resistive, low resistive, or high resistive based on their conductivity. Zero resistive materials conduct electricity with almost zero resistance below a transition temperature. Low and high resistive materials are used for conductors and resistors.
3) The classical free electron theory and quantum free electron theory are discussed as ways to explain electrical conductivity in metals based on their electronic structure and behavior of free electrons.
This document discusses various electrical concepts including static electricity, conductors and insulators, magnetic fields, direct and alternating current, capacitance, resistance, impedance, and skin impedance. Some key points:
- Static electricity is caused by an excess or deficit of electrons on objects and can cause sparks. Conductors readily allow electron flow, insulators do not, and semiconductors have intermediate conductivity.
- A changing magnetic field induces electric current in a conductor. Electromagnets have stronger magnetic fields than normal magnets.
- Direct current flows one way, alternating current oscillates. The volt measures potential difference based on power and current.
- Capacitors store electric charge between conducting plates
1. Electric current is the flow of electric charge carriers in a conductor. Current carriers include electrons in metals, ions in electrolytes, and both electrons and holes in semiconductors.
2. The electromotive force (EMF) of a cell is the potential difference between its electrodes in an open circuit. A cell's EMF depends on the electrodes, electrolyte composition and concentration, and temperature.
3. Ohm's law states that the current through a conductor is directly proportional to the potential difference across it, provided the conductor's physical conditions remain constant. Resistance depends on the material and dimensions of the conductor.
The charged particles whose flow in a definite direction constitutes the electric current are called current carriers. e.g. electrons in conductors, ions in electrolyte, electrons and holes in semiconductor.
This document summarizes key concepts in electricity and electromagnetism. It discusses static electricity, conductors and insulators, magnetic fields, direct and alternating current, current measurement using galvanometers, electromagnetic flowmeters, heat production from current flow, units like the volt and ampere, electrical burns, diathermy, capacitance and electric charge, and defibrillators. Key points include how rubbing amber produces static electricity, how conductors allow electron flow, how magnetic fields are produced by current flow and changed by ferromagnetic materials, and how alternating current oscillates direction while direct current flows one way. Measurement devices like galvanometers and flowmeters rely on the interaction of electric currents and magnetic fields. Safety concepts regarding
Electricity is the flow of electrons in a circuit. Current is the flow of electric charge, measured in amperes (A). The direction of electron flow is opposite to the direction of conventional current. Resistance is a measure of how much a material opposes the flow of electric current. Resistance depends on the material's resistivity, length, and cross-sectional area. According to Ohm's law, the current through a conductor is directly proportional to the voltage applied. Cells can be connected in series, where the total voltage is the sum of individual voltages, or parallel, where the total current is the sum of individual currents.
Current Electricity and Effects of CurrentOleepari
Electric current, potential difference and electric current. Ohm’s law; Resistance, Resistivity,
Factors on which the resistance of a conductor depends. Series combination of resistors,
parallel combination of resistors and its applications in daily life. Heating effect of electric
current and its applications in daily life. Electric power, Interrelation between P, V, I and R
Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. Resistance is a measure of opposition to current flow and depends on the material, length, and cross-sectional area of the conductor. The heating effect of electric current is used in various appliances like electric bulbs, heaters, and irons where a conductor is heated by the passage of current. Electric power is defined as the rate at which electrical energy is transferred by a circuit and is measured in watts.
This document discusses key concepts related to electricity including current, potential, electromotive force, internal resistance of cells, resistance of conductors, Ohm's law, resistivity, conductivity, and combinations of resistors. It defines current as the rate of flow of charge and describes how current, potential, resistance, and resistivity are calculated. It also explains how resistance and resistivity change with temperature and the formulas for calculating equivalent resistance when resistors are combined in series or parallel.
The document discusses key concepts in electricity including:
1) Electric current is defined as the rate of flow of electric charge per unit time, with the SI unit being amperes.
2) Resistance is a measure of how an object opposes the passage of electric current, with the SI unit being ohms.
3) Conductors contain free electrons that allow electric current to flow through the material, while insulators do not allow electron flow.
4) Ohm's law states that the current through a conductor is directly proportional to the voltage applied.
The document discusses electric current and resistance. It covers topics like:
1) Electric current is the flow of electric charge through a region of space. Current is measured in amperes and its direction is defined as the flow of positive charges.
2) Resistance arises due to collisions between electrons carrying current and fixed atoms in a conductor. Resistance depends on a material's resistivity and geometry.
3) Ohm's law states that the current through a conductor is directly proportional to the voltage applied across it. Materials that obey this relationship are called ohmic.
This document discusses key concepts in medical physics related to electric current and circuits. It begins by defining electric current as the flow of charge and discusses its units. It then explains how potential difference and a conduction pathway are needed to produce current. Electromotive force is introduced as the maximum potential difference provided by a battery due to chemical reactions. Ohm's law relates current, voltage, and resistance. Resistors in series and parallel are examined. Alternating current is also covered.
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1. 3.CURRENT ELECTRICITY
Coaching for 8-10th, PU I & II (Sci. & Commerce), NTSE, Olympiad, KVPY, NDA, CET, NEET, JEE. Call: 9663320948 Page 45
Electric Current : The rate of flow of charge through any cross-section is called current.
So if through a cross-section, dQ charge passes in time dt then instantaneous current is
given by 𝑰 =
𝒅𝑸
𝒅𝒕
and for steady flow of charges 𝑰 =
𝑸
𝒕
Current is a scalar quantity. It's S.I. unit is Ampere (A)
The direction of current : The conventional direction of current is taken to be the
direction of flow of positive charge.
Types of current : Electric current is of two type
Alternating current (ac): The current in which its direction and magnitude changes
periodically.
Direct current (dc): The current which has constant direction and magnitude.
Conductor: The material which allow flow of charges(electrons) through it are called as
conductors. Free electrons are responsible for current in conductors.
Example :Metals like copper, steel etc and water
Consider when no electric field is present. The electrons will be moving due to
thermal motion in all possible direction. Hence number of electrons travelling in any
direction will be equal to the number of electrons travelling in the opposite direction. So,
there will be no net electric current.
The charged particles whose flow in a definite direction constitutes the
electric current are called current carriers. In different situation current carriers are
different.
(i) Solids : In solid conductors like metals current carriers are free electrons.
(ii) Liquids : In liquids current carriers are positive and negative ions.
(iii) Gases : In gases current carriers are positive ions and free electrons.
(iv) Semi conductor : In semi conductors current carriers are holes and free electrons.
2. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 46
CURRENT DENSITY (j)
The amount of electric current flowing per unit cross-sectional area of a material .
Current density at point P is given by 𝒋 =
𝑰
𝑨
The SI unit of the current density are A/m2
If the cross-sectional area is not normal to the current, the cross-sectional area
normal to current in th direction of flow of charges is taken
𝒋 =
𝑰
𝑨 𝐜𝐨𝐬 𝜽
Conduction of Current in Metals: According to modern views, a metal consists of a
‘lattice’ of fixed positively charged ions in which billions and billions of free electrons are
moving randomly at speed which at room temperature (i.e. 300 K) in accordance with
kinetic theory of gases is given by
𝑣𝑟𝑚𝑠 = √
3𝑘𝑇
𝑚
= √
3 × 1.3 × 10−23 × 300
9.1 × 10−31
= 105
𝑚/𝑠
Numerical:-The number density of free electrons in a copper conductor estimated is
8.5 × 1028 m–3. How long does an electron take to drift from one end of a wire 3.0 m long to
its other end? The area of cross-section of the wire is 2.0 × 10–6 m2 and it is carrying a
current of 3.0 A.
i
𝑗
⃗
𝐴
⃗
𝑗
⃗
𝐴
⃗
i
𝐴
⃗𝑐𝑜𝑠𝛳
𝜃
,
3. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 47
OHM’S LAW
Statement:If physical conditions of a conductor such as temperature remains unchanged,
then the electric current (I) flowing through the conductor is directly proportional to the
potential difference (V) applied across its ends.
𝑉 ∝ 𝐼
𝑉 = 𝐼𝑅
where R is the electrical resistance of the conductor.
Electrical Resistance(R): The opposition offered by any conductor in the path of flow of
current is called its electrical resistance.
Its SI unit is ohm (Ω) and its dimensional formula is [𝑀L2
T−3
A−2].
Dependence of Resistance of a conductor
1)It directly proportional to the length of conductor, 𝑅 ∝ 𝑙
Thus, doubling the length of a conductor doubles the resistance
3)Resistance R is inversely proportional to the cross-sectional area, 𝑅 ∝
1
𝐴
𝑅 ∝
𝑙
𝐴
𝑹 = 𝝆
𝒍
𝑨
Where the constant of proportionality ρ depends on the material of the conductor but
not on its dimensions ρ is called resistivity.
Hence using Ohm’s law
V=IR = 𝐼𝜌
𝑙
𝐴
𝐸𝑙 = 𝑗𝜌𝑙 but V=El
𝑬 = 𝒋𝜌 or 𝒋 = 𝜎𝑬
The above relation between magnitudes of E and j in a vector form of ohm’s law.
Note:
Resistivity has unit ohm meter(Ωm).
Resistivity of a material depend on temperature and nature of the material.
It is independent of dimensions of the conductor, i.e., length, area of cross-
section .
,
4. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 48
Resistivity of metals increases with increase in temperature as
ρt = ρo (1 + αt). where ρo and ρt are resistivity of metals at O°C and t°C
and ‘α’ temperature coefficient of resistivity of the material.
For metals ‘α’ is positive, for some alloys like nichrome, manganin and
constantan, α is positive but very low.
For semiconductors and insulators. α is negative.
Velocities of charged particle (electron) in a conductor
**THERMAL VELOCITY :Due to temperature and thermal energy electrons have a
thermal velocity of 105 ms-1 . This velocity is in all directions and of magnitudes varying
from zero to maximum. Due to large number of electrons we can assume that vector sum
of thermal velocities at any instant is zero.
**Mean Free path : The path between two consecutive collisions is called free path. The
average length of these free paths is called “Mean Free Path”.
**Relaxation Time : The time to travel mean free path is called Relaxation Period or
Relaxation Time, denoted by Greek letter Tau “τ”.
**Drift Velocity(Vd) :When Electric Field is applied across a conductor, the free electrons
experience a force in the direction opposite to field. Due to this force they start drifting in
the direction of force. The Velocity of this drift is called drift velocity “Vd”
“The average velocity attained by charged particles, (eg. electrons) in a material
due to an electric field.”
Relation between drift-velocity (Vd) and electric field(E) applied.
OR Expression for drift velocity
When electric field is applied across a conductor each electron experience a Force,
F = qE in the direction of force. But according to Newton’s second law F=ma
qE=ma bur for electron q=e
𝑎 =
𝑒𝐸
𝑚
− − − − − −(1)
above equation represents acceleration of electron due to electric field. There for electron
is drifted due to this acceleration and attains drift velocity(Vd) is given by
v = u+at
but for electron v= Vd
u=0 ms-1(Initial Thermal velocity of electrons)
a=Acceleration of electron from equation (1)
t=τ (Relaxation time)
𝑽𝒅 =
𝒆𝑬
𝒎
𝝉
,
5. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 49
RELATION OF CURRENT AND DRIFT VELOCITY: Drift velocity is the average uniform
velocity acquired by free electrons inside a metal by the application of an electric field
which is responsible for current through it.
If suppose for a conductor
l= length of the conductor
n = Number of electron per unit volume of the conductor
A = Area of cross-section
V = potential difference across the conductor
E = electric field inside the conductor
Then volume of the conductor is given by =Al
If the conductor contains ‘n’ number of free electron in unit volume then number of
electrons in conductor is = nAl
If “e” be the charge on the electron then total charge on conductor is
𝑄 = 𝑛𝑒𝐴𝑙----------------------------------(1)
Time taken by electron to cross the length of conductor is
𝑡 =
𝑙
𝑉𝑑
-----------------------(2) 𝑡𝑖𝑚𝑒 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑠𝑝𝑒𝑒𝑑
Since current is the rate of charges through conductor
𝐼 =
𝑄
𝑡
-----------------------(3)
substituting eqn. (1) and (2) in equation (3) we get
𝐼 =
𝑛𝑒𝐴𝑙
𝑙
𝑉𝑑
⁄
= 𝑛𝑒𝐴𝑉𝑑
𝑰 = 𝒏𝒆𝑨𝑽𝒅 substituting 𝑉𝑑 =
𝑒𝐸
𝑚
𝜏
𝐼 =
𝐴𝑛𝑒2𝜏𝐸
𝑚
by definition of current density
𝑗 =
𝐼
𝐴
=
𝐴𝑛𝑒2
𝜏𝐸
𝐴𝑚
,
6. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 50
𝑗 =
𝑛𝑒2𝜏𝐸
𝑚
----------(4)
But ohms law in vector form written as 𝒋 = 𝜎𝑬 and 𝜎 =
1
𝜌
----conductivity
Substituting in equation (4) we get
𝝈 =
𝒏𝒆𝟐
𝝉
𝒎
Electrical Conductivity (𝜎) :The reciprocal of resistivity is called electrical conductivity.
𝜎 =
1
𝜌
Its SI units is ohm-1 m-1 or mho m-1 or siemen.m-1 .
Mobility(µ): Mobility ‘µ’ defined as the magnitude of the drift velocity per unit electric
field.
𝜇 =
𝑉𝑑
𝐸
i.e 𝜇 =
𝑒𝜏
𝑚
Its SI unit is m2 s-1V-1 and its dimensional formula is [M-1T2A], mobility is positive.
NUMERICAL: Estimate the average drift speed of conduction electrons in a copper wire of
cross-sectional area 1.0 × 10–7 m2 carrying a current of 1.5 A. Assume that each copper atom
contributes roughly one conduction electron. The density of copper is 9.0 × 103 kg/m3 , and
its atomic mass is 63.5 u.(Ans: 1.1 mm/s)
Ohmic Conductors :Those conductors which obey Ohm’s law, are called ohmic
conductors e.g., all metallic conductors are ohmic conductor.
For ohmic conductors V – I graph is a straight line.
Non-ohmic Conductors: Those conductors which do not obey Ohm’s law, are called non-
ohmic conductors. e.g., diode valve, triode valve, transistor , vacuum tubes etc.
For non-ohmic conductors V – I graph is not a straight line.
,
7. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 51
LIMITATIONS OF OHM’S LAW
1) Ohm’s law is not fundamental law in nature.
2) Ohm’s law does not applicable for non metallic conductors.
3) Ohm’s law does not hold good at high temperature.
4) This law does not obeyed by vacuum tubes, discharge tubes, semiconductors and
electrolyte.
RESISTIVITIES OF SOME MATERIALS
Characteristic curve of a diode: Negative
and positive values of the voltage and current.
Variation of current versus voltage for GaAs.
There is more than one value of V for the same current
I
,
8. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 52
DIFFERENCE BETWEEN RESISTANCE AND RSISTIVITY
TYPES OF RESISTORS
1)Wire bound resistors
Wire bound resistors are made by winding the wires of an alloy, viz., manganin,
constantan, nichrome or similar ones. These resistances are typically in the range of a
fraction of an ohm to a few hundred ohms.
2)Carbon resistors
Carbon resistors are compact, inexpensive and thus find wide use in electronic
circuits. Resistors of the higher range are made mostly from carbon. Carbon resistors are
small in size and hence their values are written using a colour code.
COLOR NUMBER MULTIPLIER TOLERANCE(%)
Black 0 1 -
Brown 1 101
-
Red 2 102
-
Orange 3 103
-
Yellow 4 104
-
Green 5 105
-
Blue 6 106
-
Violet 7 107
-
Gray 8 108
-
white 9 109
-
Gold - 10-1
5
Silver - 10-2
10
No colour - - 20
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9. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 53
Rules to calculate Resistance of a given resistor:
1. The first two bands from the left end indicate the first two significant digits of the
resistance in ohms.
2. The third band indicates the decimal multiplier (as listed in Table).
3. The last band stands for tolerance or possible variation in percentage about the
indicated values.
4. If this last band is absent then that indicates a tolerance of 20%.
For example: If the four colours are orange, blue, yellow and gold, the resistance
value is 36 × 104 Ω, with a tolerence value of 5%. i.e R=(36 × 104 ± 5%) Ω
Examples
Circuit symbol of resistors
R=(47000±5%)Ω
R=(22±5%)Ω
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10. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 54
Homework:- Find the resistance of the resistors having following colour codes.
1) Yellow-Violet-Orange-Gold Color Code
2) Green-Red-Gold-Silver Color Code
3) White-Violet-Black Color Code
4) Orange-Orange-Black-Brown-silver Color Code
5) Brown-Green-Grey-Silver Color Code
6) Red-Red-Red-Silver color code
7) Yellow-Violet-Brown-Gold color code
TEMPERATURE DEPENDENCE OF RESISTIVITY: The resistivity of a material is found
to be dependent on the temperature. the resistivity of a metallic conductor is
approximately given by,
ρT = ρ0 [1 + α (T–T0 )]
Where ρT is the resistivity at a temperature T and ρ0 is the same at a temperature T0 .
α is called the temperature co-efficient of resistivity, and the dimension of α is K–1
Variation of resistivity for some materials are shown below(1marks)
In a metal like copper, the resistivity of increases with increasing temperatures,
because ‘n’ is not dependent on temperature and thus the increase K.E of electron which
decrease in the value of ‘τ’ with rise in temperature causes ρ to increase.
For Nichrome (which is an alloy of nickel, iron and chromium) resistivity least
dependence of temperature . Manganin and constantan have similar properties. These
materials are thus widely used in wire bound standard resistors since their resistance values
would change very little with temperatures(1mark).
A)COPPER B)NICHROME C)SEMICONDUCTOR
Resistivity
Resistivity
Resistivity
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11. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 55
For insulators and semiconductors, ‘n’ increases with temperature which decrease
in τ for such materials, ρ decreases with temperature.
NOTE:-Resistance of conductor at temperature T is given by
Numerical:-The resistance of the platinum wire of a platinum resistance thermometer at
the ice point is 5 Ω and at steam point is 5.39 Ω. When the thermometer is inserted in a hot
bath, the resistance of the platinum wire is 5.795 Ω. Calculate the temperature of the bath.
Ans:(t=345.65 °C)
ELECTRICAL ENERGY, POWER
Electrical energy can be due to either kinetic energy or potential energy due to the
relative positions of charged particles or electric fields.
E = QV
Where, Q is charge and V is the potential difference
Unit:- Joule(J) , Kilowatt-hour(kWh), Electron-Volt(eV)
POWER: It is the rate at which work is done or energy is transformed in an electrical
circuit. Simply put, it is a measure of how much energy is used in a span of time.
P=VI P = I2R P = V2/R
Where, V is the potential difference (volts), I is the electric current, R is resistance
Unit:- Watt(W) or joule per second( Js-1)
Commercial unit of power is Kilo watt hour(kwh)
1𝑘𝑤ℎ = 3.6 × 106
𝐽𝑜𝑢𝑙𝑒
Numerical
1)At room temperature (27.0 °C) the resistance of a heating element is 100 Ω. What is the
temperature of the element if the resistance is found to be 117 Ω, given that the temperature
coefficient of the material of the resistor is 1.70 × 10–4 °C–1 .
2) A negligibly small current is passed through a wire of length 15 m and uniform cross-
section 6.0 × 10–7 m2 , and its resistance is measured to be 5.0 Ω. What is the resistivity of the
material at the temperature of the experiment?
RT = R0 [1 + α (T–T0 )]
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12. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 56
COMBINATION OF RESISTORS – SERIES AND PARALLEL
Series: Two resistors are said to be in series if only one of their end points is joined with
second resistor and so on
.
Parallel: Two or more resistors are said to be in parallel if one end of all the resistors is
joined together and similarly the other ends joined together
Effective resistance of the two resistors connected in series(3marks)
Consider two resistors R1, R2 and R3 in series. The charge which leaves R1 must be
entering R2 this means that the same current I flows through R1 and R2 and R3. By Ohm’s
law,
Potential difference across R1 = V1 = I R1---------------(1)
Potential difference across R2 = V2 = I R2---------------(2)
The potential difference V across the combination is V1 +V2 . Hence, from (1) & (2)
V= V1 +V2 But V= IReq
IReq = I R1+I R2
Req = R1+R2
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13. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 57
For n number of resistors the effective resistance of the combination is given by
Req = R1+R2 + R3+R4…………………..+ Rn
Note: Equivalent resistance is greater than the maximum value of resistance in the
combination.
Effective resistance of the two resistors connected in parallel.(3marks)
Consider three resistors R1, R2 and R3 in connected in parallel. The current entering
from left is divided into three parts as I1, I2 & I3 , but potential difference across each
resistor is same. Hence
I=I1+I2+I3 ----------(1)
By ohms law V=I1R1 i.e I1 =
𝑉
𝑅1
--------------------------(3)
V=I2R2 i.e I2 =
𝑉
𝑅2
---------------------------(2)
V=I3R3 i.e I3 =
𝑉
𝑅3
---------------------------(4)
V=IReq i.e I=
𝑉
𝑅𝑒𝑞
for combination
Substituting eqn.(2), (3) and (4) in eqn. (1) we get
𝑉
𝑅𝑒𝑞
=
𝑉
𝑅1
+
𝑉
𝑅2
+
𝑉
𝑅3
𝟏
𝑹𝒆𝒒
=
𝟏
𝑹𝟏
+
𝟏
𝑹𝟐
+
𝟏
𝑹𝟑
For n number of resistors the equivalent resistance is
𝟏
𝑹𝒆𝒒
=
𝟏
𝑹𝟏
+
𝟏
𝑹𝟐
+
𝟏
𝑹𝟑
+ … … … … … . . +
𝟏
𝑹𝒏
Note: Equivalent resistance is smaller than the individual value of resistance in the
combination.
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14. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 58
CELLS, EMF, INTERNAL RESISTANCE
Electric Cell: An electric cell is a device which converts chemical energy into electrical
energy.
Electric cells are of two types
(i) Primary Cells: Primary cells cannot be charged again. Voltic, Daniel and Leclanche
cells are primary cells.
(ii) Secondary Cells : Secondary cells can be charged again and again. Acid and alkali
accumulators are secondary cells.
Electro – motive – Force (emf) of a Cell :
The energy given by a cell in flowing unit positive charge throughout the circuit
completely one time, is equal to the emf of a cell.
Emf of a cell (E) = W/q.
Its SI unit is volt.
Terminal Potential Difference of a Cell:
The energy given by a cell in flowing unit positive charge through till outer circuit
one time from one terminal of the cell to the other terminal of the cell.
Terminal potential difference (V) = W / q.
Its SI unit is volt.
Internal Resistance of a Cell(r): The opposition offered by the electrolyte of a cell in the
path of electric current is called internal resistance (r) of the cell.
Internal resistance of a cell
(i) Increases with increase in concentration of the electrolyte.
(ii) Increases with increase in distance between the electrodes.
(iii) Decreases with increase in area of electrodes dipped in electrolyte.
Relation between E, V and r
If cell of EMF, 𝜀 and internal resistance, r are connected to an external
resistance ,R then circuit has total resistance (R+r). Then current in the circuit is given by
𝐼 =
𝜀
𝑅+𝑟
𝜀 = 𝐼(𝑅 + 𝑟) but V=IR
𝑉 = 𝜀 − 𝐼𝑟
Above equation tells us that V is always less than 𝜀.
Solve numerical 3.5 from NCERT
Book
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15. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 59
Combination of cells
Group of cell is called a battery. Like resistors, cells can be combined together in an
electric circuit. And like resistors, for calculating currents and voltages in a circuit,
replace a combination of cells by an equivalent cell.
CELLS IN SERIES:- Consider two cells in series , where one terminal of the two cells is
joined together leaving the other terminal in either cell free. ε1 , ε2 are the emf’s of the two
cells and r1 , r2 their internal resistances, respectively. Current through each cell is same
(I).
We know for cell , 𝑉 = 𝜀 − 𝐼𝑟 applying this equation to each cell we get
𝑉1 = 𝜀1 − 𝐼𝑟1 and 𝑉2 = 𝜀2 − 𝐼𝑟2
V = 𝑉1 + 𝑉2 but 𝑉 = 𝜀𝑒𝑞 − 𝐼𝑟𝑒𝑞
𝜀𝑒𝑞 − 𝐼𝑟𝑒𝑞 = 𝜀1 − 𝐼𝑟1 + 𝜀2 − 𝐼𝑟2
𝜀𝑒𝑞 − 𝐼𝑟𝑒𝑞 = 𝜀1 + 𝜀2 − 𝐼(𝑟2 + 𝑟2)
Comparing left hand side and right hand side of aove equation we can write
𝜺𝒆𝒒 = 𝜺𝟏 + 𝜺𝟐 and 𝒓𝒆𝒒 = (𝒓𝟐 + 𝒓𝟐)
1)The equivalent emf of a series combination of ‘n’ cells is just the sum of their
individual emf’s,
2) The equivalent internal resistance of a series combination of ‘n’ cells is just the sum of
their internal resistances
𝜺𝟏 𝜺𝟐
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16. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 60
CELLS IN PARALLEL:- Consider two cells in parallel having ε1 , ε2 are the emf’s of the
two cells and r1 , r2 their internal resistances, respectively. Current through each cell is
split ed as 𝐼1 & 𝐼2.
Hence net current through combination is
𝐼 = 𝐼1 + 𝐼2 ---------------(1)
We know for cell 𝑉 = 𝜀 − 𝐼𝑟 hence solving for current I we get 𝐼 =
𝜀−𝑉
𝑟
Applying above equation to each cell 𝐼1 =
𝜀1−𝑉
𝑟1
& 𝐼2 =
𝜀2−𝑉
𝑟2
For equivalent circuit , 𝐼 =
𝜀𝑒𝑞 − 𝑉
𝑟𝑒𝑞
From equation (1)
𝜀𝑒𝑞 − 𝑉
𝑟𝑒𝑞
=
𝜀1 − 𝑉
𝑟1
+
𝜀2 − 𝑉
𝑟2
𝜀𝑒𝑞
𝑟𝑒𝑞
− 𝑉 (
1
𝑟𝑒𝑞
) =
𝜀1
𝑟1
+
𝜀2
𝑟2
− 𝑉 (
1
𝑟1
+
1
𝑟2
)
Comparing LHS and RHS
𝜺𝒆𝒒
𝒓𝒆𝒒
=
𝜺𝟏
𝒓𝟏
+
𝜺𝟐
𝒓𝟐
and
𝟏
𝒓𝒆𝒒
=
𝟏
𝒓𝟏
+
𝟏
𝒓𝟐
By solving and substituting
𝜀𝑒𝑞 =
𝜀1𝑟2+𝜀2𝑟1
𝑟1+ 𝑟2
and 𝑟𝑒𝑞 =
𝑟1+𝑟2
𝑟1𝑟2
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17. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 61
KIRCHHOFF’S RULES:
Kirchhoff's laws are used to help us understand how current and voltage work
within a circuit. They can also be used to analyze complex circuits that can't be solved by
equivalent resistance using series and parallel resistors.
There are two Kirchhoff’s laws for solving complicated electrical circuits.
1) Kirchoff’s first law : This law is also known as junction rule or current law (KCL).
According to it I = 0. The algebraic sum of currents meeting at a junction is zero
This law has significance of conservation of charge(1marks)
2) Kirchoff’s second law: This law is also known as loop rule or voltage law (KVL) and
according to it “the algebraic sum of the changes in potential in complete traversal of a
mesh (closed loop) is zero”, i.e. ∑V = 0
This law has significance of conservation of energy(1marks)
For loop 1) V - I1R1- I2R4
For loop 2) –I3R2- I3R3+ I3R4
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18. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 62
Solve the following using Kirchoff’s law’s
WHEATSTONE BRIDGE
Wheatstone bridge is an arrangement of four resistance which can be used to
measure one of them in terms of rest. It is an application of Kirchhoff’s rules.
Construction: The bridge has four resistors R1 , R2 , R3 and R4 . Across one pair of
diagonally opposite points (A and C in the figure) a source is connected. Between the
other two vertices, B and D, a galvanometer G (which is a device to detect currents) is
connected.
Balancing Condition for Wheatstone bridge: In the Balanced Bridge condition, the
current through the galvanometer is zero. 𝑖. 𝑒 𝐼𝑔 = 0
We apply Kirchhoff ’s loop rule to closed loops ADBA and CBDC.
−𝐼1𝑅1 + 0 + 𝐼2𝑅2 -----(1) 𝐼𝑔 = 0
−𝐼2𝑅4 + 0 + 𝐼3𝑅3-------(2) but 𝐼2 = 𝐼4 𝑎𝑛𝑑 𝐼3 = 𝑅1
Find R3 Find I1, I2 and I3
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19. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 63
METER BRIDGE
Meter Bridge is an instrument that is used to find the unknown resistance of a coil, wire or
any other material. This bridge works under the principle of Wheatstone bridge.
Construction:
The meter bridge consists of a wire of length 1m and of uniform cross sectional
area stretched and clamped between two thick metallic strips bent at right angles L
shape.
𝐼1𝑅1 = 𝐼2𝑅2 -----(3)
𝐼1𝑅3 = 𝐼2𝑅4 -----(4)
Dividing equation (3) & (4) we get
𝑅1
𝑅3
=
𝑅2
𝑅4
OR
𝑹𝟐
𝑹𝟏
=
𝑹𝟒
𝑹𝟑
This last equation relating the four
resistors is called the balance condition
for the galvanometer to give zero or null
deflection.
Solve numerical 3.8 from NCERT Book
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20. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 64
The metallic strip has two gaps across which resistors(R and S) are connected.
The end points where the wire is clamped are connected to a cell through a key.
One end of a galvanometer is connected to the metallic strip midway between the
two gaps. The other end of the galvanometer is connected to a ‘jockey’.
The jockey is essentially a metallic rod whose one end has a knife-edge which can
slide over the wire to make electrical connection.
By the balancing condition when galvanometer reads zero
𝑹
𝑺
=
𝒍𝟏
𝟏𝟎𝟎−𝒍𝟏
Thus, once we have found out 𝒍𝟏 , the unknown resistance R is given b
𝑹 =
𝑺𝒍𝟏
𝟏𝟎𝟎−𝒍𝟏
Note: The material of wire used in meter bridge is made of manganin because it is an alloy
has high resistivity and a low value of temperature coefficient of resistance. Thick copper
strips are used in meter bridge because copper is a good conductor of electricity.
POTENTIOMETER
Potentiometer is a device mainly used to measure emf of a given cell and to compare
emf’s of cells. It is also used to measure internal resistance of a given cell
The principle of a potentiometer is that the potential dropped across a segment
of a wire of uniform cross-section carrying a constant current is directly proportional to
its length.
Solve numerical 3.9 from NCERT Book
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21. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 65
Application of potentiometer:
1) Compare emf of two cell.
𝜀1
𝜀2
=
𝑙1
𝑙2
2) Find internal resistance of cell. 𝑟 = 𝑅 (
𝑙1
𝑙2
− 1)
NOTE:The potentiometer has the advantage that it draws no current from the voltage
source being measured. As such it is unaffected by the internal resistance of the source.
ELECTRICAL NETWORK
An electrical network is an interconnection of electrical network elements, such as
resistances, capacitances, inductances, voltage, and current sources.
NODE:
When two or more circuit element meet, at any point on a circuit is called a node
LOOP:
Loop is any closed path in the circuit formed by branches.
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22. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 66
ONE MARK QUESTIONS
1. Define steady current in a conductor.
2. Give the SI unit of electric current.
3. How many electrons per second constitute a current of one micro ampere?
4. Is electric current a scalar or vector quantity?
5. How many electrons flow per second through a conductor carrying a current of 0.5 mA?
6. What is the conventional direction of electric current?
7. Name the current carriers in metals or solid conductors.
8. Name the current carriers in electrolytic solutions or liquid conductors.
9. Name the current carriers in discharge tubes or gaseous conductors.
10.Define resistance of a metallic conductor.
11.Write the SI unit of resistance.
12.Define SI unit of resistance.
13.How does the resistance of a conductor depend on its length?
14.How does the resistance of a conductor depend on its area of cross section?
15.Define electrical conductance.
16.Mention the SI unit of conductance.
17.Define resistivity of a material of a conductor.
18. A wire of given resistivity is stretched to three times its length .What will be its new resistivity?
19.Mention the relation between the resistance and resistivity?
20.Mention the SI unit of resistivity?
21.Define the term current density (j).
22.Write the SI unit of current density.
23.Is current density a scalar or a vector quantity?
24.Define electrical conductivity.
25.Mention the relation between current density and conductivity.
26.What is the effect of relaxation time of electrons on the conductivity of a metal?
27.Define electron mobility.
28.Mention the SI unit of mobility.
29.Write the expression for mobility in terms of relaxation time.
30. Name a material whose resistivity decreases with the rise of temperature.
31. How does the resistance of an insulator change with temperature?
32.Write the colour code for the resistors of resistance 500Ω, 5KΩ, 37Ω, 4.5X103Ω.
33.The colour sequence is Brown, black, red and gold on a resistor. Write its resistance value.
34.Draw a graph indicating the variation of resistivity of copper with temperature.
35.Represent graphically the variation of resistivity of nichrome with temperature.
36.Draw a graph indicating the variation of resistivity of a semiconductor withtemperature.
37.How does the resistance of a conductor vary with temperature?
38.What happens to the resistivity of a conductor when the temperature is increased?
39.How does the resistivity of a semiconductor vary with temperature?
40.Name a material which exhibits very weak dependence of resistivity with temperature?
41.Why manganin or constantan are used to make resistance coils.
42.When are the two resistors said to be in series?
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23. 3.CURRENT ELECTRICITY
Coaching for 8-10th Page 67
43.When resistors are said to be in parallel?
44.Define emf of a cell?
45.Define internal resistance of a cell.
46.Give the expression for the potential difference between the electrodes of a cell of emf ‘E’ and internal
resistance ‘r’?
47.Write the expression for equivalent emf when two cells of emf E1 and E2 connected in series.
48.What is an electric network?
49.What is a node or junction in an electrical network?
50.What is a mesh or loop in an electrical network?
51.What is the significance of junction rule or KCL?
52.What is the significance of KVL or loop rule?
53.Write the balancing condition for Wheatstone’s network.
54.What is the principle of Meter Bridge?
55.Mention one use of Meter Bridge.
56.Write the equation used to compare emf of two cells in terms of balancing length in potentiometer
experiment.
57.Give the formula to determine the internal resistance of the cell using potentiometer.
TWO MARK QUESTIONS
1. Write any two differences between resistance and resistivity.
2. Define the terms (1) drift velocity (2) relaxation time.
3. Obtain an expression for acceleration of an electron in a current carrying conductor.
4. State and explain Ohm’s law.
5. Write the limitations of ohm’s law.
6. Mention the factors on which resistivity of a metal depend.
7. Write the expression for resistivity in terms of number density and relaxation time.
8. Mention any two factors on which resistance of a conductor depends.
9. State another equivalent form of ohm’s law in terms of current density and conductivity and explain
the terms.
10. A cell of emf 2V and internal resistance 1 Ω is connected across a resistor of 9 Ω. find the terminal
potential difference of the cell.
11. Draw V-I graph for ohmic and non- ohmic materials.
12. How does the resistance of (1) good conductor, (2) semiconductor vary with increase in temperature?
13. Which are the two major types of resistors commercially made?
14. To make resistors of high range which material is used and why?
15. Mention the factors on which internal resistance of a cell depend.
16. For what basic purpose, the cells are connected (1) in series (2)in parallel?
17. Define electrical power and write its S.I unit.
18. State and explain Kirchhoff’s junction rule/ current law.
19. State and explain Kirchhoff’s loop rule / voltage law.
20. Mention two uses of potentiometer.
21. Why the connecting resistors in a meter bridge are made of thick copper strips?
22. The potential difference between the terminals of an electric iron is 240 V and the current is 5.0A.
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24. 3.CURRENT ELECTRICITY
th Page 68
What is the resistance of the electric iron?
23. A potential difference of 20 volts is applied across the ends of a resistance of 5 Ω. What current will
flow in the resistor? (4 A)
24. A current of 5 A flows through a wire whose ends are at a potential difference of 3 volts. Calculate the
resistance of the wire. (0.6Ω)
25. An electric bulb draws a current of 0.35 A for 20 minutes. Calculate the amount of electric charge that
flows through the circuit. (420 C)
THREE MARK QUESTIONS
1. Arrive at the expression for electric current in terms of drift velocity.
2. derive the expression for current density in terms of electric field and conductivity of the material
using ohm’s law.
3. Arrive at the relation between terminal potential difference and emf of a cell using ohm’s law.
4. Obtain the expression for effective resistance of two resistors in series.
5. Obtain the expression for effective resistance of two resistors in parallel.
6. What is the principle of Meter Bridge? Arrive at the expression for the (unknown) resistance using
Meter Bridge.
FIVE MARK QUESTIONS
1. Explain how resistance depends on the dimensions of the conductor and hence arrive at the
expression for resistivity,
2. Assuming the expression for current in terms of drift velocity, deduce Ohm’s law.
3. Obtain the expression for the equivalent emf and internal resistance of two cells connected in series.
4. Obtain the expression for the equivalent emf and internal resistance of two cells connected in parallel.
5. Deduce the condition for balance of Wheat stone's network using Kirchhoff’s laws.
,