Electromagnetic Concepts for JEE Main & Advanced

Faraday’s law of electromagnetic induction:

• Explains the generation of electromotive force (EMF) in a conductor when the magnetic flux linked with it changes. Key Points:
  • EMF(ε) = -dΦ/dt
  • Negative sign indicates opposing nature.

Lenz’s Law:

• Describes the direction of induced EMF and current flow according to the conservation of energy. Key points:
  • Opposes the change in magnetic flux.
  • Induced current produces a magnetic field that counteracts the change.

Magnetic Flux(Φ)

• Represents the amount of magnetic field passing through a given area. Key Points:
  • Defined as the dot product of magnetic field strength (B) and area vector (A)
  • Φ = B⋅Acosθ.

Electromotive Force (EMF):

• Work done in moving a unit charge around a closed loop due to electromagnetic induction. Key Points:
  • Unit: Volt (V)
  • Can be expressed as the rate of change of magnetic flux.

Induced Current:

• The flow of electric charges in a conductor due to electromagnetic induction. Key Points:
  • Magnitude determined by the rate of change of magnetic flux.
  • Direction given by Lenz’s law.

Self-inductance (L):

• Property of a conductor that opposes changes in its own current flow. Key Points:
  • Coefficient that relates the change in magnetic flux to the rate of change of current.
  • Expressed as L = Φ/I

Mutual Inductance (M):

• Interaction between two different conductors where the change in current of one induces an EMF in the other. Key points:
  • Coefficient relating induced EMF in one coil to the rate of change of current in the other.
  • M = Φ/I

Energy Stored in a Magnetic Field:

• Represents the energy contained within a magnetic field. Key Points:
  • U = (1/2)LI^2
  • Proportional to the square of current flowing through the inductor.

AC Generators:

• Devices that convert mechanical energy into alternating current (AC) electricity. Key Points:
  • Utilize electromagnetic induction.
  • Rotating coils induce EMF in stationary conductors.

AC Motors:

• Machines that convert electrical energy into mechanical energy using alternating current (AC). Key Points:
  • Work on the principle of electromagnetic induction in reverse.
  • Rotating magnetic field created by multiple alternating currents.

Transformers:

• Devices that transfer electrical energy from one circuit to another by electromagnetic induction. Key Points:
  • Consist of primary and secondary coils with different numbers of turns.
  • EMF induced in the secondary coil according to Faraday’s law.

Key Concepts for CBSE Boards:

Faraday’s Law of Electromagnetic Induction:

• Explains how changing magnetic fields induce electromotive force (EMF) and electric currents.

Lenz’s Law:

• Describes the direction of induced EMF and current according to the conservation of energy.

AC Generators:

• Convert mechanical energy into alternating current (AC) electricity using electromagnetic induction.

AC Motors:

• Convert electrical energy into mechanical energy using alternating current (AC) and electromagnetic induction.

Basic Idea of Self-Inductance and Mutual Inductance:

• Self-inductance opposes changes in current flow in a single conductor, while mutual inductance involves the interaction between two conductors where the change in current of one induces an EMF in the other.