Magnetism & Electromagnetism

5 min

Master Magnetic Fields, Induction, Motors & Transformers for Competitive Exams

Core Golden Rule

Electricity and magnetism are deeply linked. A changing magnetic field produces electricity via Faraday induction, while electric current creates a magnetic field.

Exam Importance

Direct questions appear on AC vs DC and transformer core materials.
Faraday and Lenz law questions test direction and magnitude concepts.
Motor and generator energy conversions are regular Railway/SSC favorites.

Memory Hooks

Motor = Electrical to Mechanical (M for Motor, M for Mechanical).
Generator = Mechanical to Electrical (G for Generator, G for Ghm-Ghm turbine).
Transformer works only on AC (Alternating Current).

Device Comparison

Device	Input Energy	Output Energy
Electric Motor	Electrical	Mechanical
Electric Generator	Mechanical	Electrical
Transformer	AC Voltage	Step-up/Down AC

Core Concepts Visualized

Electromagnet

(Soft iron core)

Soft iron core

Used in electric bells and cranes.

Faraday Law

(Flux change induces EMF)

Flux change induces EMF

Moving magnet lights up a coil.

AC vs DC

(Frequency & direction)

Frequency & direction

AC reverses direction periodically.

Transformer

(Mutual induction principle)

Mutual induction principle

Works only with alternating current.

Exam Traps & Pitfalls

Transformer works on DC currentTransformer works only on AC

DC produces constant magnetic flux, hence no mutual induction.

Magnetic field lines intersectMagnetic field lines never intersect

Intersection would mean two directions of magnetic field at one point.

Generator creates energy from nothingGenerator converts mechanical to electrical

Law of conservation of energy always applies.

Quick Exam Drill

Q1.Which device is used to convert mechanical energy into electrical energy?

Q2.Why can a transformer NOT be used with a direct current (DC) source?

Page 12 of 45