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CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction

Here we have provided CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction for the ease of students so that they can prepare better for their exams.
authorImageAnanya Gupta2 Sept, 2024
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CBSE Class 12 Physics Notes Chapter 6

CBSE Class 12 Physics Notes Chapter 6: Here are the notes for CBSE Class 12 Physics Chapter 6 Electromagnetic Induction. This chapter explains the phenomenon of electromagnetic induction, where a changing magnetic field induces an electric current in a conductor.

The chapter covers important concepts such as Faraday's Law of Induction, Lenz's Law, and the concept of eddy currents. Understanding these principles is important as they form the basis for many electrical devices, such as transformers and electric generators. These notes will help you grasp the key points and prepare effectively for your exams.

CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction Overview

These notes are prepared by subject experts of Physics Wallah and provide an in-depth overview of CBSE Class 12 Physics Chapter 6 Electromagnetic Induction. These notes are designed to help students understand how changing magnetic fields can create electric currents, a principle that is essential in various applications like transformers, electric motors, and generators. These expert-prepared notes will help students in mastering the key concepts and excelling in their exams.

CBSE Class 12 Physics Notes Chapter 6 PDF Download

Here we have provided CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction PDF for the ease of students so that they can prepare better for their exams by downloading the PDF easily and using it without any internet.

CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction PDF

CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction

Here we have provided CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction-

Magnetic Flux

As per the Class 12 Physics Chapter 6 Notes, magnetic flux in any area equals the total number of magnetic field lines of force passing through that area. Net flux through an area A having, under the magnetic influence of B, can be given as Magnetic flux = ɸ = B. dA = BAcosΘ Where, B = magnetic flux through an area A = area under consideration = angle between area vector and magnetic field vector.
  • Case 1:
When the value of = 0 ɸ = BA
  • Case 2:
When the value of = 90 ɸ = 0 Some important Properties as covered in our Class 12 Physics Chapter 6 Notes:
  • Magnetic flux is denoted by ɸ.
  • Flux is a scalar quantity.
  • The SI unit of magnetic flux is Weber (Wb).
  • The CGS unit of magnetic flux is maxwell or gauss.
  • 1 Wb = 108 gauss.
  • The dimensional formula of flux is [ ɸ ] = [M L2 T-2 A-2].

Electromagnetic Induction

Electromagnetic induction is a process where a changing magnetic flux in a closed loop induces an electromotive force (emf). When a current flowing through a coil changes, it alters the magnetic field around it, which in turn induces an emf in the coil or in nearby conductors. This induced emf leads to the generation of an induced current if the circuit is closed. The phenomenon is fundamental to many technologies, including transformers, electric generators, and inductors.

Faraday’s Law of EMI:

There are two laws under Faraday’s Law of EMI.
  • Law 1:
Law 1 states that whenever a change of magnetic flux is linked with any circuit, an emf is induced, which lasts as long as the change in magnetic flux continues.
  • Law 2:
According to the Second Law, the magnitude of emf induced is directly proportional to the rate of change of magnetic flux. ∝ dɸ / dt Therefore, induced emf = e = N (dɸ / dt) Where N = number of turns pf coil Induced Current: Induced current = i = e/R = N/R (dɸ / dt) Induced Charge: Induced charge = dq = i dt = N/R (dɸ) Induced charge is independent of time Induced power = P = e2/R = N2/R (dɸ / dt)2 How to produce induced EMF: EMF or electromotive force is induced in any circuit whenever there is a change in magnetic flux. But, this emf can be induced in many ways. As magnetic flux = ɸ = BAcosΘ Hence, flux ɸ can be changed when any B, A or  is altered. Therefore, the following ways can be used to induce EMF:
  • By changing/ adjusting magnetic field B.
  • By changing the area under consideration, A.
The area can be altered by stretching, shrinking or modifying the coil’s shape.
  • By changing the angle .
This can be done by modifying the surface’s area and the magnetic field’s relative orientation.

Lenz’s Law

Lenz’s Law states that the direction of the induced emf or current in a circuit always opposes the change in magnetic flux that caused it This law is rooted in the principle of conservation of energy. For a better understanding, let's consider how the magnetic field and force change depending on the position of the magnet relative to the coil:
Position of Magnet Direction of Induced Current Behavior of Coil’s Face Type of Magnetic Force Magnetic Field Linked with Coil
Towards the coil Anticlockwise North pole Repulsive force Increases
Away from the coil Clockwise South pole Attractive force Decreases
Towards the coil Clockwise South pole Repulsive force Increases
Away from the coil Anticlockwise North pole Attractive force Decreases

Eddy Current

Eddy currents are loops of electric current induced within conductors when there is a change in magnetic flux. These currents are formed in a large piece of conductor and have significant magnitudes, often generating considerable heat due to the low resistance of the material. According to Lenz's law of electromagnetic induction, these currents swirl in a manner that creates a magnetic field opposing the change in flux, resulting in energy loss primarily in the form of heat.

Properties of Eddy Currents:

  • Eddy currents are similar to water eddies, circulating in closed loops within the conductor.
  • Also known as "Foucault currents," named after the scientist who first proposed their experimental hypothesis.
  • The generation of eddy currents leads to electrical energy loss as heat, often considered undesirable in many applications.

Applications of Eddy Currents: While energy loss due to eddy currents is usually minimized, in some cases, this effect is harnessed for specific applications:

  • Braking Systems: In trains, roller coasters, and certain power tools like electric saws and drills, eddy currents are used to provide braking force. The magnetic interaction with the metal wheels slows down the vehicle smoothly.
  • Induction Furnaces: Eddy currents generate heat in metals, aiding in processes like melting and alloy formation.
  • Induction Cooking: Eddy currents are also utilized in induction cooking, where they heat the cookware directly.
  • Adjustable Speed Drives: Eddy currents, controlled by a feedback system, help in achieving adjustable speed drives in various machinery.

Induced Charge Flow

When a changing magnetic flux induces a current in a circuit, a charge flows through the circuit as a result. The total charge that flows through the circuit, due to this induced current, can be calculated by integrating the current over the time interval during which the flux is changing. This net charge Q flowing through the circuit can be expressed as: q = i dt = 1/R  dɸ/dt  dt = 1/R dɸ q = Δɸ / R and   q = N Δɸ / R where N = number of turns

Induced Electric Field

In Class 12 Physics Chapter 6, it is explained that the induced electric field is non-conservative and non-electrostatic. Unlike electrostatic fields, the electric field generated by a changing magnetic field does not have a potential function and cannot be described simply by a gradient of a scalar potential. Instead, the field lines form concentric circles and create closed loops around the region where the magnetic flux is changing.

Motional EMF in a Loop by Generated Area

When a conducting rod moves through a magnetic field, it generates an electromotive force (EMF) in a loop formed by the rod and two parallel conducting rails. This phenomenon is utilized to understand how motional EMF is induced due to the movement of a conductor in a magnetic field. Here’s how it works:
  • Setup: Imagine a setup with two parallel conducting rails and a conducting rod that slides along these rails. The rails are connected to form a closed loop with the rod.
  • Movement: As the rod moves through the magnetic field, it sweeps out an area between the rails. This area changes as the rod moves, causing a change in the magnetic flux through the loop.

Periodic EMI

When a rectangular coil with N turns rotates in a uniform magnetic field, an electromotive force (EMF) is periodically induced in the coil due to the changing magnetic flux. Here’s a breakdown of the process: Having ⍵ its angular speed, v = frequency of coil’s rotation, R = resistance of the coil Hence, a flux is linked to the coil due to uniform rotational motion, which is given as, ɸ = NBA cosΘ = NBA cos⍵t ɸ = ɸocos⍵t where ɸo = NBA = maximum flux.

Induced EMF

The electromotive force (EMF) induced in a coil or conductor changes in response to variations in magnetic flux. This change can occur in different patterns depending on the nature of the magnetic field and the movement of the coil or conductor. When the EMF changes in a repeating or cyclical pattern, it is referred to as Periodic EMF. This typically happens when the conductor or coil is exposed to a magnetic field that varies periodically with time, such as in the case of a rotating coil in a uniform magnetic field. Periodic EMF occurs due to the continuous change in the magnetic flux linked with the coil, which is a result of its rotational motion or the changing magnetic field. This results in a sinusoidal variation of the induced EMF over time, which can be mathematically described using Faraday’s Law of Electromagnetic Induction. The EMF varies in a regular, predictable pattern, making it periodic. Induced emf is given as, e = dɸ/dt = NBA⍵ sin⍵t E = eo sin⍵t where eo = maximum emf = NBA⍵ = ɸo⍵

Induced current

At any time t, the induced current i is given as, i = e/R = eo/R sin⍵t = io sin⍵t Where io = maximum current or current amplitude

Inductance

Inductance is a fundamental property of electrical circuits that opposes changes in current. When the current through a coil changes, it alters the magnetic flux around the coil. According to Faraday’s Law of Electromagnetic Induction, this changing flux induces an electromotive force (EMF) in the coil that opposes the change in current. This process is known as self-induction, and the induced EMF is often referred to as back-EMF. Inductance measures how much a coil or circuit resists changes in current. A higher inductance means greater opposition to current changes. For a straight wire carrying current without any iron core, the inductance is relatively low compared to a coil with an iron core, which significantly enhances the inductance. Understanding inductance can be challenging for many students. To grasp these concepts more effectively students are encouraged to refer to our Class 12 Physics Chapter 6 Notes where our subject experts break down these complex ideas into simpler more understandable explanations. Self-inductance Self-inductance is a phenomenon where an emf is induced by changing the current in the coil. Some important Properties:
  • L deNotes the inductance of self-inductance.
  • The SI unit of inductance is Henry and denoted by H.
  • The dimensional formula of inductance is [ M L2 T-2 A-2 ].
  • Coefficient of self induction = L = Nɸ /i.
Where N = number of turns of the coil ɸ = magnetic flux And i = current flowing through the coil. Self-inductance for conductors:
  • Self inductance for circular coil is = L = µoN2A /2R.
Where r = radius of circular coil, N = number of turns, A = area of circular coil = πR2.
  • Self-inductance of a solenoid = L = µoN2A /l.
Where l= length of solenoid, N = number of turns.
  • Self-inductance for a square coil is L = 2√2 µoN2a / π.
  • Energy stored in an inductor = 12LI².
Dependency of inductance:
  • Self-inductance or L does not depend on the current flowing through the coil/conductor.
  • Instead, L depends on the number of turns or N, area of cross-section A, and permeability of medium µ.
  • Moreover, self-inductance or L only begins to show whenever there is a change in current.

Benefits of CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction

  • Comprehensive Coverage : The notes cover all essential topics, including magnetic flux, Faraday's Law, Lenz's Law, eddy currents, and induced EMF, ensuring students have a thorough understanding of electromagnetic induction.
  • Clear Explanations : Concepts are explained in simple and easy-to-understand language, making complex ideas like Lenz's Law and self-induction more accessible.
  • Illustrative Examples : The notes include practical examples and illustrations, helping students visualize and grasp the concepts better.
  • Important Formulas and Equations : Key formulas and equations, such as those for induced EMF and magnetic flux are clearly presented making it easier for students to remember and apply them during exams.
  • Problem-Solving Techniques : The notes provide step-by-step solutions to common problems, aiding in effective problem-solving skills and exam preparation.
  • Preparation for Exams : The notes are designed to help students review and reinforce their understanding, making them well-prepared for both board exams and competitive tests.
CBSE Physics Notes For Class 12 – Chapter-wise
Chapter 1 Electric Charges and Fields
Chapter 2 Electrostatic Potential and Capacitance
Chapter 3 Current Electricity
Chapter 4 Moving Charges and Magnetism
Chapter 5 Magnetism and Matter
Chapter 6 Electromagnetic Induction
Chapter 7 Alternating Current
Chapter 8 Electromagnetic Waves
Chapter 9 Ray Optics and Optical Instruments
Chapter 10 Wave Optics
Chapter 11 Dual Nature of Radiation and Matter
Chapter 12 Atoms
Chapter 13 Nuclei
Chapter 14 Semiconductor Electronics: Materials, Devices, and Simple Circuits

CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction FAQs

What is electromagnetic induction?

Electromagnetic induction is the process by which a changing magnetic field induces an electromotive force (EMF) or voltage in a conductor. This phenomenon was discovered by Michael Faraday and is described by Faraday's Law of Induction.

What is Faraday's Law of Electromagnetic Induction?

Faraday's Law states that the induced EMF in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.

What is Lenz's Law?

Lenz's Law states that the direction of the induced current is such that it opposes the change in magnetic flux that produced it. This law is a consequence of the conservation of energy.

What are eddy currents?

Eddy currents are loops of electric current induced within conductors by a changing magnetic field. They can cause significant energy loss in the form of heat due to the resistance of the material.

What is self-induction?

Self-induction is the phenomenon where a changing current in a coil induces an EMF in the same coil, opposing the change in current. The property of a coil to resist changes in current is called inductance.
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