Detailed Notes from Toppers on Electromagnetic Induction

1. Faraday’s Law of Electromagnetic Induction (NCERT Class 12, Chapter 6)

- Basic concept:

• When a conductor is placed in a changing magnetic field, an electromotive force (EMF) is induced in the conductor.
• This phenomenon is known as electromagnetic induction.

- Lenz’s Law:

• The direction of the induced EMF is such that it opposes the change in magnetic flux.
• This law determines the polarity of the induced EMF.

2. Motional Electromotive Force (EMF) (NCERT Class 12, Chapter 6)

- Motion of a conductor in a magnetic field:

• When a conductor moves in a magnetic field, an EMF is induced in the conductor.
• The magnitude of the induced EMF depends on the strength of the magnetic field, the velocity of the conductor, and the length of the conductor.

- Factors affecting the magnitude of induced emf:

• Strength of the magnetic field
• Velocity of the conductor Length of the conductor Angle between the magnetic field and the velocity of the conductor

3. Eddy Currents (NCERT Class 12, Chapter 6)

- Formation and effects of eddy currents:

• Eddy currents are circular electric currents that are induced in a conductor when it is exposed to a changing magnetic field.
• Eddy currents can cause energy losses and heating in the conductor.

- Methods to minimise eddy current losses:

• Using laminated cores
• Using high-resistivity materials
• Using magnetic shields

- Applications of eddy currents:

• Electric motors and generators
• Induction heating
• Metal detectors
• Magnetic brakes

4. Inductance (NCERT Class 12, Chapter 6)

- Self-inductance:

• When a current flows through a coil, it creates a magnetic field.
• This magnetic field induces an EMF in the coil, which opposes the change in current.
• This phenomenon is known as self-inductance.

- Mutual inductance:

• When two coils are placed close together, the magnetic field created by one coil induces an EMF in the other coil.
• This phenomenon is known as mutual inductance.

- Calculation of self-inductance and mutual inductance:

• The self-inductance of a coil depends on the number of turns in the coil, the area of the coil, and the permeability of the core material.
• The mutual inductance between two coils depends on the number of turns in each coil, the area of the coils, the distance between the coils, and the permeability of the core material.

5. Energy Stored in Magnetic Field (NCERT Class 12, Chapter 6)

- Magnetic field energy:

• When a current flows through a coil, it stores energy in the magnetic field created by the coil.
• The amount of energy stored depends on the strength of the magnetic field and the volume of the coil.

- Calculation of magnetic field energy:

• The magnetic field energy stored in a coil is given by the formula: $$U_m = \frac{1}{2}LI^2$$ Where:
  • $$U_m$$ is the magnetic field energy in joules
  • $$L$$ is the inductance of the coil in henrys
  • $$I$$ is the current flowing through the coil in amperes

6. Alternating Current (AC) Circuits (NCERT Class 12, Chapter 7)

- Basic concepts of AC circuits:

• Alternating current (AC) is a current that periodically reverses direction.
• The voltage and current in an AC circuit are represented by sine waves.
• The frequency of an AC current is the number of times the current changes direction per second.

- Phase difference between voltage and current:

• In an AC circuit, the voltage and current may not be in phase with each other.
• The phase difference between voltage and current is determined by the inductive and capacitive elements in the circuit.

- Reactance and impedance:

• Reactance is the opposition to the flow of alternating current caused by inductance and capacitance.
• Impedance is the total opposition to the flow of alternating current, which includes both resistance and reactance.

7. Transformer (NCERT Class 12, Chapter 7)

- Principle of operation:

• A transformer is a device that transfers electrical energy from one circuit to another through electromagnetic induction.
• A transformer consists of two coils, a primary coil, and a secondary coil, which are wound around a common iron core.

- Types of transformers:

• Step-up transformers: increase the voltage of the AC supply
• Step-down transformers: decrease the voltage of the AC supply
• Autotransformers: transformers with a single winding that has multiple taps

- Efficiency of a transformer:

• The efficiency of a transformer is defined as the ratio of the output power to the input power.
• The efficiency of a transformer is always less than 100% due to losses such as hysteresis, eddy currents, and copper losses.

8. AC Generator (NCERT Class 12, Chapter 7)

- Construction and working principle:

• An AC generator is a device that converts mechanical energy into electrical energy.
• An AC generator consists of a rotating armature coil placed in a stationary magnetic field.
• As the armature coil rotates, it cuts through the magnetic field, which induces an alternating EMF in the coil.

- Types of AC generators:

• Single-phase generators: produce a single-phase AC current
• Three-phase generators: produce a three-phase AC current

9. AC Motors (NCERT Class 12, Chapter 7)

- Basic principles of AC motors:

• AC motors are devices that convert electrical energy into mechanical energy.
• AC motors operate on the principle of electromagnetic induction.

- Types of AC motors:

• Synchronous motors: run at a constant speed, which is synchronized with the frequency of the AC supply

-Induction motors: run at a speed that is slightly less than the synchronous speed

10. Power Transmission and Distribution (NCERT Class 12, Chapter 7)

- Power transmission and distribution systems:

• Power transmission and distribution systems are used to transmit electrical energy from generating stations to consumers.
• Power transmission and distribution systems consist of transmission lines, distribution lines, transformers, and substations.

- Losses in power transmission:

• Power losses occur during the transmission and distribution of electrical energy.
• Power losses are mainly caused by resistance in the transmission lines and transformers.