CBSE Class 12 Physics Notes Chapter 6 Electromagnetic Induction

Electromagnetic induction is the phenomenon wherein a changing magnetic field induces a current in a conductor. 

• In electric generators, spinning magnets within coils induce current, powering homes and industries.
• Current flowing through coils interacts with permanent magnets in electric motors, creating the rotational force powering everything from fans to high-speed trains.
• In microphones, sound waves vibrate a diaphragm, which in turn moves a coil in a magnetic field, inducing a current that translates sound into electrical signals.
• Powerful magnetic fields and radio waves create detailed images of human anatomy in MRI machines.

Some real-life applications of electromagnetic induction are - 

• Electromagnetic waves from a charging pad induce current in your phone's coil, eliminating the need for wires.
• Stepping up or down the voltage in power lines relies on the induction principle to efficiently transmit electricity.

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Class 12 Physics Chapter 6 Notes - Electromagnetic Induction

Experiments Of Faraday And Henry

Micheal Faraday and Joseph Henry found that a moving conducting loop in the magnetic field of a magnet induces an electromotive force (EMF) and electric current starts flowing through it, as long as the conducting loop moves in the magnetic field i.e. Relative motion between a magnetic dipole and a closed coil produces a small current in the coil.

First Experiment

• Relative motion between a magnet and a conducting coil induces emf in the conducting coil.
• Whenever there is a relative motion between a closed coil and a magnet, induced emf setup across the coil.
• Large induced emf or current is produced in the coil if the relative motion between the magnet and the coil is large.
• Induced current lasts in the coil, as long as the magnet moves with respect to the coil.

Second Experiment

• Relative motion between a current-carrying coil and a conducting coil induced emf in the conducting coil.
• When a current carrying coil moves towards or away from the conducting coil, magnetic flux linked with the conducting coil changes.
• This produces induced emf or current in the conducting coil.

Third Experiment

• Changing current in a current carrying coil induces emf in a nearby coil without relative motion between them.
• On or Off the switch of a current carrying coil changes the strength of magnetic field produced by it.
• When this changing magnetic field links with a nearby conducting coil, an emf is induced in it.
• In this experiment, the coil has no relative motion yet changing current induces emf in the nearby coil.

Experiments Of Faraday And Henry

Magnetic Flux

Magnetic flux is a measure of the quantity of magnetic field lines passing through a given surface.

• Formula: It is mathematically represented as the product of magnetic field strength (B), surface area (A), and the angle (θ) between the magnetic field and the normal to the surface.
• Φ=B⋅A⋅cosθ.
• Unit: The unit of magnetic flux in the International System of Units (SI) is the Weber (Wb).
• Dimensional Formula: [M L² T² A^-1]

Faraday’s Law Of Induction

• Faraday’s First Law: Whenever magnetic flux linked with a conductor (or coil) changes, an emf is induced in it. This induced emf lasts as long as the magnetic flux continues in the coil.
• Faraday’s Second Law: The magnitude of induced emf is directly proportional to the rate of change of magnetic flux linked with the conductor (or coil).
• According to Faraday’s law, we have

EMF, ε = dɸ/dt

Where 

• ε is the induced emf
• ɸ is the magnetic flux.

• Applications: This law is fundamental to operating generators, transformers, and various electrical devices.

Lenz’s Law And Conservation Of Energy

• Lenz's Law Principle states that the direction of an induced electromotive force (EMF) in a circuit will oppose the change in magnetic flux that produced it.
• According to Lenz’z Law, the polarity of induced emf is given by

EMF, ε = – dɸ/dt

• If the coil has N number of turns, then induced emf is given by

EMF, ε = – N (dɸ/dt)

• Formulated by Heinrich Lenz in 1834 as an essential part of electromagnetic induction.
• Lenz's Law aligns with the principle of energy conservation, ensuring that the work done to induce an EMF is accounted for by the opposing current.
• Demonstrates the conversion of mechanical energy (or other forms) into electrical energy while preserving the overall energy balance.

Motional Electromotive Force

Motional Electromotive Force (EMF) is induced in a conductor moving through a magnetic field, creating a potential difference across the conductor.

• Principle: According to Faraday's Law, the magnitude of the induced EMF is proportional to the rate of change of magnetic flux through the conductor.
• Formula: The motional EMF (ε) can be calculated using the formula 

ε = B * v * l

Where 

• B is the magnetic field strength
• v is the velocity of the conductor
• l is the length of the conductor perpendicular to the magnetic field.

• The formula for motional induced emf in a conducting rod rotated in magnetic field is

ε = 1/2 Bl²ω

Where 

• B is the magnetic field strength
• ω is the angular velocity of the conductor
• l is the length of the conductor

Inductance

• Inductance is the property of a circuit element resisting changes in current.
• Induces voltage when the current in a circuit changes.

Self Inductance

• It is also known as the Inertia of Electricity as it opposes the growth or decay of the current in the lopp.
• Magnetic flux is found to be proportional to the current.
• Formula:

L = ɸ/I

Where

• L is the coefficient of self induction or Self inductance.
• ɸ is the magnetic flux
• I is the current.

• Unit: Henry (H)

Self Inductance of a Solenoid

• Formula:

L = μ_on²AL

Where

• μ_o is the absolute permeability of the medium.
• n is the number of turns per unit length.
• L is the length of the solenoid

Mutual Inductance:

• Mutual Induction is the phenomenon of inducing emf in a coil due to change of current with time in a nearly coil.
• Mutual inductance of two coils is defined as the magnetic flux linked with the secondary coil due to the flow of unit current in the primary coil.
• Formula:

M = ɸ_S/I_P

Where

• M is the coefficient of mutual induction or Mutual inductance.
• ɸ_S is the magnetic flux linked with the secondary coil
• I_P is the current in the primary coil.

Mutual inductance of two long co-axial Solenoid

• Formula:

M = (μ_oN₁N₂A)/L

Where

• μ_o is the absolute permeability of the medium.
• N₁ is the number of turns in first solenoid.
• N₂ is the number of turns in second solenoid.
• A is the area of cross section of the solenoid
• L is the length of each solenoid

Mutual inductance of two concentric coils of different radii

• Formula:

M = μ_o/4π (2π²r₁² / r₂²)

Where

• μ_o is the absolute permeability of the medium.
• r₁ is the radius of the first coil.
• r₂ is the radius of the second coil.

Grouping of Coils (Equivalent Inductance)

• Coils in Series:

L = L₁ + L₂ + L₃ + ……….

• Coils in Parallel:

1/L = 1/L₁ + 1/L₂ + 1/L₃ + ……….

Aligned with the latest syllabus, these notes are essential for board exams and beneficial for competitive exams like JEE and NEET. CBSE Class 12 Physics Unit - 4 with Chapters 6 and 7, carry 8 marks in the CBSE board exams. With an 8% weightage in competitive exams, these notes prepare you comprehensively. 

There are Some important List Of Top Physics Questions On Electromagnetic Induction Asked In CBSE CLASS XII