Course Content
Class 12th Physics Chapter 1 Electric Charges And Fields
NCERT Solutions for Chapter 1 for Class 12 Physics talks about factors and topics related to Electric Charge and Fields. Some of the prominent topics covered in the Chapter are Conductors And Insulators, Charging By Induction, Basic Properties Of Electric Charge, Coulomb’s Law, etc.
Class 12th Physics Chapter 2 Electrostatic Potential And Capacitance
NCERT Solutions for Chapter 2 for Class 12 Physics talks about Electrostatic Potential in detail. The chapter revolves around relevant topics such as Potential Due To A Point Charge, Potential Due To An Electric Dipole, Potential Due To A System Of Charges, Equipotential Surfaces, etc.
Class 12th Physics Chapter 3 Current Electricity
NCERT Solutions for Chapter 3 for Class 12 Physics is an important chapter from weightage point of view. This chapter is very scoring and can be a very interesting chapter for students. The chapter talks about Electric Current, Ohm’s Law, Drift Of Electrons And The Origin Of Resistivity, Limitations Of Ohm’s Law, Resistivity Of Various Materials, etc.
Class 12th Physics Chapter 4 Moving Charges And Magnetism
Chapter 4 for Class 12 Physics can be a very scoring chapter for Class 12 students. However, it is equally complex to understand. It talks about Magnetic Force, Motion In A Magnetic Field, Motion In Combined Electric And Magnetic Fields, etc.
Class 12th Physics Chapter 5 Magnetism And Matter
NCERT Solutions for Chapter 5 for Class 12 Physics talk about topics related to Magnetism and Matter such as the Bar Magnet, Magnetic field lines, The electrostatic analogue, Magnetism And Gauss’s Law, The Earth’s Magnetism, Magnetic declination and dip, Magnetic Properties Of Materials, Diamagnetism, Paramagnetism, Ferromagnetism.
Class 12th Physics Chapter 6 Electromagnetic Induction
A very interesting and Chapter, this one in particular talks about The Experiments Of Faraday And Henry, Magnetic Flux, Faraday’s Law Of Induction, Lenz’s Law and Conservation Of Energy.
Class 12th Physics Chapter 7 Alternating Current
NCERT Solutions for Chapter 7 for Class 12 Physics talk about Ac Voltage Applied To A Resistor, Phasor-diagram solution, Analytical solution, Resonance, Oscillations, and Transformers.
Class 12th Physics Chapter 8 Electromagnetic Waves
In this chapter students will learn about Displacement Current, Electromagnetic Waves, Sources of electromagnetic waves and other such topics related to Electromagnetic Waves.
Class 12th Physics Chapter 9 Ray Optics and Optical Instruments
NCERT Solutions for Chapter 9 for Class 12 Physics talks about Reflection Of Light By Spherical Mirrors, Refraction, Total Internal Reflection and other topics related to Ray Optics.
Class 12th Physics Chapter 10 Wave Optics
NCERT Solutions for Chapter 10 for Class 12 Physics talk about Huygens Principle, Refraction and Reflection Of Plane Waves Using Huygens Principle, Refraction Of A Plane Wave, Refraction At A Rarer Medium etc.
Class 12th Physics Chapter 11 Dual Nature Of Radiation And Matter
Chapter 11 for Class 12 Physics is a scoring chapter. If learnt the concepts thoroughly, it can help students to score high marks in their Physics exam. This chapter talks about Electron Emission, Photoelectric Effect, Hertz’s observations, Hallwachs’ and Lenard’s observations, etc.
Class 12th Physics Chapter 12 Atoms
Chapter 12 for Class 12 Physics is a very interesting yet very confusing chapter for the students. It talks about topics: Alpha-Particle Scattering and Rutherford’s Nuclear Model Of Atom, Alpha-particle trajectory, Electron orbits, Atomic Spectra etc.
Class 12th Physics Chapter 13 Nuclei
NCERT Solutions for Chapter 13 for Class 12 include all answers to the questions included in the textbook. Additionally, the solutions explain topics such as Atomic Masses And Composition Of Nucleus, Size Of The Nucleus, Mass-energy And Nuclear Binding Energy, etc in detail.
Class 12th Physics Chapter 14 Semiconductor Electronics Materials Devices And Simple Circuits
Chapter 14 for Class 12 Physics Is a very scoring and interesting chapter and revolves around topics such as Intrinsic Semiconductor, Extrinsic Semiconductor, P-n Junction, Semiconductor Diode, Application Of Junction Diode As A Rectifier etc.
Class 12th Physics Chapter 15 Communication Systems
NCERT Solutions for Chapter 15 for Class 12 Physics talks about topics related to the communication systems. The important topics are Elements Of A Communication System, Basic Terminology Used In Electronic Communication Systems, etc. This is a very interesting chapter in the Class 12 Physics textbook.
Frequently asked questions (FAQs) Related to Course
Here are some frequently asked questions (FAQs) that could be relevant for your Class 12 Physics Online Course: 1. What is the Class 12 Physics Online Course offered by Free-Education (Wisdom Academy)? Our Class 12 Physics Online Course is a comprehensive learning program designed to help students excel in their CBSE Board exams. It includes chapter-wise notes, important questions, solved and unsolved previous year question papers, video explanations, interactive classes, and more. 2. Who is the instructor for this course? The course is curated and taught by Er. Mohd Sharif, an experienced educator with over 13 years of teaching Physics. He is also the founder of Wisdom Education Academy & Free-Education.In. 3. How can I access the course materials? Once you enroll in the course, you will gain access to our online learning platform. All course materials, including notes, videos, and question papers, can be accessed from there at any time. 4. Are the notes and resources provided in downloadable formats? Yes, our chapter-wise notes and other resources are available in downloadable PDF formats. This allows you to study even when you're offline. 5. How can I ask questions or clear doubts during the course? We offer doubt clearance through online classes, where you can interact with the instructor directly and get your queries resolved. You can also use our platform's messaging system to communicate with the instructor. 6. Are there regular tests to review my preparation? Absolutely, we believe in consistent evaluation. The course includes regular review tests to gauge your understanding and track your progress. 7. Can I access the course on mobile devices? Yes, our online learning platform is mobile-friendly, allowing you to access the course materials on various devices like smartphones and tablets. 8. Are there any prerequisites for enrolling in this course? This course is designed for Class 12 students studying Physics. It's tailored to cover all topics and concepts within the Class 12 Physics curriculum. 9. How can I enroll in the Class 12 Physics Online Course? Enrolling is simple. Visit our website, navigate to the Class 12 Physics Course, and follow the enrollment instructions. 10. Is there a refund policy in case I'm not satisfied with the course? Yes, we have a refund policy in place. If you're not satisfied with the course within the first 7 days, you can request a refund according to our refund policy. 11. Can I interact with other students in the course? Yes, we encourage collaborative learning. Our platform may include discussion forums or other means for students to interact and share insights. 12. Are there any additional resources provided apart from the course materials? In addition to the course materials, we may provide supplementary resources like articles, study tips, and external references to enhance your learning experience. For any other questions or clarifications, feel free to reach out to our support team at (8750387081).
Class 12 Physics Online Course: Notes, Important Questions, and Previous Year Papers
About Lesson



Electric Current (I)

The rate of flow of charge through any cross-section of a wire is called electric current flowing through it.

Electric current (I) = q / t. Its SI unit is ampere (A).

The conventional direction of electric current is the direction of motion of positive charge.

The current is the same for all cross-sections of a conductor of non-uniform cross-section. Similar to the water flow, charge flows faster where the conductor is smaller in cross-section and slower where the conductor is larger in cross-section, so that charge rate remains unchanged.

If a charge q revolves in a circle with frequency f, the equivalent current,

i = qf

(In a metallic conductor current flows due to motion of free electrons while in electrolytes and ionized gases current flows due to electrons and positive ions.)

Types of Electric Current

According to its magnitude and direction electric current is of two types

(i) Direct Current (DC) Its magnitude and direction do not change with time. A ceil, battery or DC dynamo are the sources of direct current.

(ii) Alternating Current (AC) An electric current whose magnitude changes continuously and changes its direction periodically is called alternating current. AC dynamo is source of alternating current.

Current Density

The electric current flowing per unit area of cross-section of conductor is called current density.

Current density (J) = I / A

Its S1 unit is ampere metre-2 and dimensional formula is [AT-2].

It is a vector quantity and its direction is in the direction of motion positive charge or in the direction of flow of current.

Thermal Velocity of Free Electrons

Free electrons in a metal move randomly with a very high speed of the order of 105 ms-1. This speed is called thermal velocity of free electron.

Average thermal velocity of free electrons in any direction remains zero.

Drift Velocity of Free Electrons

When a potential difference is applied across the ends of a conductor, the free electrons in it move with an average velocity opposite to direction of electric field. which is called drift velocity of free electrons.

Drift velocity vd = eEτ / m = eVτ / ml

where, τ = relaxation time, e = charge on electron,

E = electric field intensity, 1 = length of the conductor,

V = potential difference across the ends of the conductor

m = mass of electron.

Relation between electric current and drift velocity is given by

vd = I / An e


The drift velocity of electron per unit electric field applied is mobility of electron.

Mobility of electron (μ) = vd / E

Its SI unit is m2s-1V-1 and its dimensional formula is [M-1T2A].

Ohm’s Law

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.

I ∝ V

or V = IR

where R is the electrical resistance of the conductor and R = Ane2 τ / ml.

Electrical Resistance

The obstruction offered by any conductor in the path of flow of current is called its electrical resistance.

Electrical resistance, R = V / I

Its SI unit is ohm (Ω) and its dimensional formula is [ML2T-3A-2].

Electrical resistance of a conductor R = ρl / A

where, l = length of the conductor, A = cross-section area and

ρ = resistivity of the material of the conductor.


Resistivity of a material of a conductor is given by

ρ = m / n2 τ

where, n = number of free electrons per unit volume.

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 etc.

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.

Resistivity is low for metals, more for semiconductors and very high alloys like nichrome, constantan etc.

(In magnetic field the resistivity of metals increases. But resistivity of ferromagnetic materials such as iron, nickel, cobalt etc decreases in magnetic field.)

Electrical Conductivity

The reciprocal of resistivity is called electrical conductivity.

Electrical conductivity (σ) = 1 / ρ = 1 / RA = ne2 τ / m

Its SI units is ohm-1 m-1 or mho m-1 or siemen m-1.

Relation between current density (J) and electrical conductivity (σ) is given by

J = σ E

where, E = electric field intensity.

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.


When few metals are cooled, then below a certain critical temperature their electrical resistance suddenly becomes zero. In this state, these substances are called superconductors and this phenomena is called superconductivity.

Mercury become superconductor at 4.2 K, lead at 7.25 K and niobium at 9.2 K

Colour Coding of Carbon Resistors

The resistance of a carbon resistor can be calculated by the code given on it in the form of coloured strips.

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 ceUs 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

The obstruction 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

E = V + Ir

r = (E / V – 1) R

If cell is in charging state, then

E = V – Ir

Grouping of Cells

(i) In Series If n cells, each of emf E and internal resistance r are connected in series to a resistance R. then equivalent emf

R = nr / m ⇒ mR = nr

Kirchhoff’s Laws

There are two Kirchhoff’s laws for solving complicated electrical circuits

(i) Junction Rule The algebraic sum of all currents meeting at a junction in a closed circuit is zero, i.e., Σ I = O.

This law follows law of conservation of charge.

(ii) Loop Rule The algebraic sum of all the potential differences in any closed circuit is zero, i.e.,

ΣV = 0 ⇒ ΣE = ΣIR

This law follows law of conservation of energy.

Balanced Wheatstone Bridge

Wheatstone bridge is also known as a metre bridge or slide wire bridge.

This is an arrangement of four resistance in which one resistance is unknown and rest known. The Wheatstone bridge as shown in figure. The bridge is said to be balanced when deflection in galvanometer is zero, i.e., ig = O.

E = Kl

or E1 / E2 = l1 / l2

Determination of Internal Resistance of a Cell using Potentiometer

The arrangement is shown in figure. If the cell E is in open circuit and balancing length l1, then

E = Kl1

Important Points

  • Potentiometer is an ideal voltmeter.
  • Sensitivity of potentiometer is increased by increasing length of potentiometer wire.
  • If n identical resistances are first connected in series and then in parallel. the ratio of the equivalent resistance.

Rs / Rp= n2 / 1

  • If a skeleton cube is made with 12 equal resistance,each having a resistance R, then the net resistance across
  1. The diagonal of cube = 5 / 6 R
  2. The diagonal of a face = 3 / 4 R
  3. along a side = 7 / 12 R
  • If a resistance wire is stretched to a greater length, keeping volume constant, then

R ∝ l2 ⇒ R1 / R2 = (l1 / l2)2

and R ∝ 1 / r4 ⇒ R1 / R2 = (r2 / r1)4

where l is the length of wire and r is the radius of cross-section area of wire.

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