Important MCQs and Solved Problems on Electromagnetic Induction and AC
FAQs on Electromagnetic Induction and Alternating Currents Practice Paper
1. What is electromagnetic induction?
Electromagnetic induction refers to the process by which a changing magnetic field produces an induced electromotive force (emf) in a conductor. This effect, discovered by Michael Faraday, is fundamental in generating alternating current (AC). Key points include:
- Occurs when the magnetic flux through a circuit varies
- Described by Faraday’s Law of Electromagnetic Induction
- Commonly used in transformers and electrical generators
2. State Faraday's laws of electromagnetic induction.
Faraday's laws of electromagnetic induction explain the relationship between magnetic fields and induced electromotive force (emf):
- First Law: Whenever the magnetic flux through a circuit changes, an emf is induced.
- Second Law: The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux through the circuit, i.e., emf = -dΦ/dt.
3. What is Lenz’s law and what is its significance?
Lenz’s law states that the direction of the induced emf and current is such that it opposes the change in magnetic flux that produced it. Its significance lies in:
- Ensuring conservation of energy
- Giving the negative sign in Faraday’s law equation: emf = -dΦ/dt
- Illustrating opposing effects in electromagnetic induction and eddy currents
4. How does an AC generator work?
An AC generator operates by rotating a coil within a magnetic field, inducing an alternating current (AC) through electromagnetic induction. The process involves:
- Mechanical energy rotating the coil
- The coil cutting magnetic flux lines, changing magnetic flux
- Induced emf produces alternating current in the external circuit
5. What are the differences between AC and DC?
Alternating Current (AC) and Direct Current (DC) differ in their flow and applications:
- AC changes direction periodically; DC flows in one direction only
- AC is used in homes and industries; DC powers batteries and electronic devices
- AC can be easily transformed to higher/lower voltages, while DC cannot
6. What is self-induction and how is it quantified?
Self-induction is the phenomenon where a changing current in a coil induces an emf in the same coil, opposing the current change. It is quantified by the self-inductance (L) of the coil:
- Measured in henry (H)
- Represented by emf = -L (di/dt), where di/dt is the rate of change of current
7. Explain mutual induction with an example.
Mutual induction occurs when a change in current in one coil induces an emf in a neighboring coil. A classic example is the transformer:
- Primary coil receives varying current, producing changing magnetic field
- Secondary coil linked magnetically experiences induced emf
- Used to change (step up/step down) AC voltage in power distribution
8. What is resonance in an AC circuit?
Resonance in an AC circuit with inductance (L) and capacitance (C) occurs when the inductive reactance equals the capacitive reactance, maximizing current flow. Key points:
- Happens at resonant frequency: f = 1/(2π√(LC))
- Current amplitude is maximum, circuit impedance is minimum
- Important in radios, filters, and tuning devices
9. What are eddy currents and what are their uses?
Eddy currents are swirling currents induced in bulk conductors when exposed to changing magnetic fields. Their uses include:
- Induction heating
- Electromagnetic braking in trains
- Metal detectors and energy meters
10. How does a transformer work in electromagnetic induction?
A transformer utilizes mutual induction to change the voltage and current levels in AC circuits. It operates by:
- Primary coil connected to AC, creates varying magnetic flux
- Secondary coil linked magnetically, where emf is induced
- Allows voltage to be stepped up or down for power distribution
11. What factors affect the magnitude of induced emf in a coil?
The magnitude of induced emf in a coil depends on several factors:
- Rate at which magnetic flux changes (dΦ/dt)
- Number of turns (N) in the coil
- Strength of the magnetic field
- Area of the coil
12. Why is AC preferred over DC for transmission of electric power?
AC is preferred over DC for electric power transmission because:
- AC voltage can be easily stepped up or down using transformers
- High voltage transmission reduces energy losses over long distances
- Generation and distribution of AC is more economically feasible






















