By the end of this chapter you'll be able to…

  • 1Describe and draw magnetic field patterns around a straight wire and a solenoid
  • 2Apply the right-hand thumb rule to find magnetic field direction around a current
  • 3Explain the motor effect: force on a current-carrying conductor in a magnetic field; apply Fleming's Left-Hand Rule
  • 4State Faraday's Law of electromagnetic induction; describe the working of a generator
  • 5Distinguish electric motor and electric generator in terms of energy conversion
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Why this chapter matters
Electromagnetism bridges electricity and magnetism — the two fundamental forces that power modern technology. Magnetic field patterns around a current-carrying wire (right-hand thumb rule), the motor effect, electromagnetic induction (Faraday's law), and the electric generator are all tested in AP SSC. The difference between a motor (electrical → mechanical) and generator (mechanical → electrical) is a standard 2-mark question. Fleming's rules (left-hand for motor, right-hand for generator) are essential directional tools.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

Electromagnetism — Class 10 Physical Science

"Oersted connected electricity and magnetism — for the FIRST time — in 1820. Within a century, his discovery had given the world motors, generators, and the entire electrical age."

1. Oersted's Discovery (1820)

A compass needle DEFLECTS when placed near a current-carrying wire. 'The electric current produces a MAGNETIC FIELD.' This was the FIRST experimental link between electricity and magnetism.

2. Right-Hand Thumb Rule

Grasp the conductor in your RIGHT hand. THUMB → direction of CURRENT (+ to −). Curled FINGERS → direction of MAGNETIC FIELD lines (circles around the wire).

3. Solenoid — A Coil of Wire

Current through a solenoid → produces a UNIFORM MAGNETIC FIELD inside — like a BAR MAGNET. One end = NORTH. Other = SOUTH. Strength increased by: MORE turns. MORE current. SOFT IRON CORE inside (→ ELECTROMAGNET). 'An electromagnet is a TEMPORARY magnet. Switch OFF the current → magnetism DISAPPEARS. Switch ON → magnet returns.'

4. Fleming's Left Hand Rule (MOTOR)

Thumb = FORCE / Motion. Index = Magnetic FIELD (N → S). Middle = CURRENT (+ to −). Used to find direction of FORCE on a current-carrying conductor in a magnetic field. DC Motor: Electrical energy → Mechanical energy.

5. Electromagnetic Induction — Faraday's Law

A CHANGING magnetic field (by moving a magnet near a coil, or a coil near a magnet) INDUCES an EMF (voltage) in a conductor. Fleming's RIGHT Hand Rule (GENERATOR) : Thumb = Motion. Index = Field. Middle = INDUCED CURRENT. AC Generator: Mechanical energy → Electrical energy.

6. AC vs DC

AC (Alternating Current)DC (Direct Current)
DirectionREVERSES periodically (50 times/sec in India = 50 Hz)CONSTANT — one direction
SourcePower plants. Generators.Batteries. Solar cells.
TransmissionCan be transmitted over LONG distances (transformed to high voltage)Cannot be easily transformed

7. Domestic Circuits

Mains: 220 V AC, 50 Hz. LIVE wire (RED/BROWN — dangerous, carries current from source). NEUTRAL wire (BLACK/BLUE — completes circuit). EARTH wire (GREEN/YELLOW — safety — connects metal body of appliance to ground). Fuse connected to LIVE wire. 'If a live wire touches the metal body → current flows to EARTH → fuse blows → circuit breaks. This SAVES LIVES.'

8. Common Mistakes

  1. Left hand = Motor (use "FBI" left: F=thumb, B=index, I=middle). Right hand = Generator.
  2. 'Current is induced whenever there is a magnetic field' — WRONG. Current is induced only when the magnetic field is CHANGING (relative motion between coil and magnet).

9. AP SSC Exam Focus

TopicMarks
Solenoid and electromagnet3-4
Fleming's rules (motor vs generator)3-4
Domestic circuits2-3
AC vs DC2-3

10. Magnetic Field Lines — Detailed Properties

  1. MAGNETIC FIELD LINES are IMAGINARY lines that represent the direction of the magnetic field.
  2. They emerge from the NORTH pole and enter the SOUTH pole (OUTSIDE the magnet). INSIDE: they go from SOUTH to NORTH.
  3. They form CLOSED LOOPS (continuous — no beginning or end).
  4. They NEVER INTERSECT each other. 'If two field lines crossed, a compass needle at that point would have to point in TWO directions — impossible.'
  5. The CLOSER the lines → the STRONGER the magnetic field.
  6. Field lines are CROWDED near the poles (strong field) and SPREAD OUT far from the magnet (weak field).

'Properties of magnetic field lines are a HIGH-SCORING 2-mark question in AP exams. Memorise: 1-direction (N to S outside), 2-closed loops, 3-never intersect, 4-closer = stronger.'

11. Magnetic Field Due to a Current-Carrying Conductor

Straight Conductor: Magnetic field consists of CONCENTRIC CIRCLES around the wire. Direction determined by RIGHT-HAND THUMB RULE. Strength ∝ current (I) and ∝ 1/distance from wire.

Circular Loop: At the CENTRE of the loop: B ∝ I (current) and B ∝ 1/r (radius). 'A coil with N turns gives N times the field of a single loop.'

Solenoid: A LONG coil of wire. Inside: UNIFORM magnetic field (same strength everywhere). Outside: field is WEAK (similar to a bar magnet). The formula for field inside: B = μ₀nI (where n = number of turns per unit length, μ₀ = permeability of free space).

12. Electromagnet — Detailed

Construction: A SOFT IRON CORE placed inside a solenoid. When current flows: the core BECOMES a magnet. When current stops: magnetism DISAPPEARS.

Why Soft Iron?: Soft iron has HIGH permeability (concentrates magnetic field) and LOW retentivity (doesn't stay magnetised when current is off). 'Steel would become a PERMANENT magnet — not suitable for an electromagnet where we want to turn it ON and OFF.'

Applications: Electric bells. Cranes in scrap yards (lift heavy iron/steel objects). MRI machines. Maglev trains. Relays and switches.

13. Electric Motor — Principle and Working

Principle: A current-carrying conductor placed in a magnetic field experiences a FORCE (Fleming's Left Hand Rule).

Construction: RECTANGULAR coil of copper wire wound on a SOFT IRON CORE (armature). Coil placed between STRONG permanent magnets. SPLIT RINGS (commutator) — two halves of a copper ring — each connected to one end of the coil. CARBON BRUSHES press against the split rings.

Working: Current flows through coil → magnetic field exerts FORCE on both sides → coil ROTATES. After half-turn: split rings REVERSE the direction of current in the coil → coil continues to rotate in the SAME direction. 'The commutator is the KEY component — it CONVERTS AC generated in the coil into DC in the external circuit, OR it REVERSES current to keep the motor spinning in one direction.'

Energy Conversion: Electrical energy → Mechanical energy.

14. Electric Generator — Principle and Working

Principle: ELECTROMAGNETIC INDUCTION (Faraday's Law). When a coil is rotated in a magnetic field: the magnetic flux through the coil CHANGES → an EMF is INDUCED.

Construction: Similar to motor: Coil (armature) between magnets. However: commutator is replaced by TWO FULL RINGS (SLIP RINGS — for AC generator) or a SPLIT RING (for DC generator).

Working: Coil rotated MECHANICALLY (by turbine, engine, or hand crank). As coil rotates: the angle between the coil and magnetic field CHANGES → induced EMF changes SINUSOIDALLY. After 180° rotation: direction of induced current REVERSES → AC output. 'In a DC generator: the commutator converts AC to DC — just like in a motor but in REVERSE.'

Energy Conversion: Mechanical energy → Electrical energy.

Difference Between Motor and Generator

FeatureElectric MotorElectric Generator
Energy ConversionElectrical → MechanicalMechanical → Electrical
PrincipleForce on current-carrying conductor in B-fieldElectromagnetic induction
Fleming's RuleLEFT hand (Motor)RIGHT hand (Generator)
Power SourceExternal currentExternal mechanical force
Key ComponentCommutator (split rings)Slip rings (AC) or commutator (DC)

15. Electromagnetic Induction — Faraday's Experiments

Experiment 1: A magnet MOVED toward a coil → GALVANOMETER shows a DEFLECTION. Magnet STOPPED → NO deflection. Magnet MOVED away → deflection in OPPOSITE direction. 'Deflection depends on MOTION — not just presence — of the magnet.'

Experiment 2: Two coils placed CLOSE. Closing switch in coil 1 (primary) → momentary deflection in coil 2 (secondary). Opening switch → deflection in OPPOSITE direction.

Faraday's Laws: (1) EMF is induced whenever magnetic flux linked with a coil CHANGES. (2) The magnitude of induced EMF is PROPORTIONAL to the RATE of change of magnetic flux. (3) The direction of induced current OPPOSES the change that produced it (Lenz's Law).

16. Domestic Electric Circuits — Safety in Detail

Earthing: The EARTH wire connects the metal body of appliances to a METAL PLATE buried deep in the ground (near zero potential). If a LIVE wire touches the metal casing: current flows to EARTH (lowest resistance path) → FUSE BLOWS → circuit breaks. 'Earthing prevents ELECTROCUTION. Without it, touching a faulty appliance could be FATAL.'

Short Circuit: When LIVE wire touches NEUTRAL wire directly (without a load). Resistance DROPS to near ZERO. Current SURGES to VERY HIGH values. Fuse/MCB TRIPS immediately. 'Short circuits can cause ELECTRICAL FIRES — that's why every circuit MUST have a properly rated fuse or MCB.'

Overloading: Plugging too many appliances into one socket → total current exceeds wire's rating → overheating → fire.

17. Self-Test

Q1: State Fleming's Left Hand Rule. A1: If we stretch the FOREFINGER, MIDDLE FINGER, and THUMB of the LEFT hand mutually PERPENDICULAR: Forefinger points in direction of MAGNETIC FIELD (N→S). Middle finger points in direction of CURRENT (+ to −). Thumb points in direction of FORCE or MOTION.

Q2: Why does a current-carrying solenoid behave like a bar magnet? A2: The current in the solenoid produces a magnetic field. Inside the solenoid, field lines are PARALLEL and UNIFORM. The field pattern OUTSIDE is IDENTICAL to that of a bar magnet: one end behaves as NORTH, the other as SOUTH. 'A magnetic compass brought near one end confirms the polarity.'

Q3: What is the role of the split rings (commutator) in a DC motor? A3: The split rings REVERSE the direction of current in the coil after every HALF TURN. This ensures the coil continues to rotate in the SAME direction (otherwise it would oscillate back and forth).

Q4: Differentiate between AC and DC generators. A4: AC generator uses SLIP RINGS (two full rings) → output current REVERSES direction periodically → AC. DC generator uses a COMMUTATOR (split ring) → output current flows in ONE direction → DC.

Q5: Why are magnetic field lines NOT allowed to intersect? A5: If two field lines intersected, the magnetic field would have TWO different directions at the SAME point. A compass needle cannot point in two directions simultaneously — so field lines NEVER intersect.

Q6: Explain how an electric bell works using electromagnetism. A6: Pressing the bell switch → current flows through the electromagnet → it attracts a SOFT IRON ARMATURE → the armature strikes the GONG. Armature movement BREAKS the circuit → electromagnet deactivates → armature SPRINGS BACK → circuit COMPLETES again → cycle repeats rapidly → CONTINUOUS ringing.

Q7: Why is soft iron preferred over steel for making electromagnets? A7: Soft iron has: HIGH PERMEABILITY (concentrates magnetic field) and LOW RETENTIVITY (loses magnetism quickly when current is OFF). Steel would become a PERMANENT magnet — unsuitable for an electromagnet that must be switched ON/OFF.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Electromagnetism
RIGHT-HAND THUMB RULE: Thumb points in direction of CURRENT → curled fingers show MAGNETIC FIELD direction (around wire). MAGNETIC FIELD IN SOLENOID: Similar to bar magnet. One end N-pole, other S-pole (use right-hand grip rule for solenoid). MOTOR EFFECT: Force on conductor = BIL sinθ. F = force. B = magnetic field strength. I = current. L = length of conductor. FLEMING'S LEFT-HAND RULE (Motor): Point LEFT HAND with: First finger = Field direction, Second finger = Current direction, Thumb = Motion direction (force). FARADAY'S LAW: EMF induced is proportional to RATE OF CHANGE of magnetic flux. LENZ'S LAW: Induced current opposes the change causing it. FLEMING'S RIGHT-HAND RULE (Generator): Right hand. First finger = Field. Second/Middle finger = induced Current direction. Thumb = Motion direction. ELECTRIC MOTOR: Electrical energy → Mechanical energy. GENERATOR: Mechanical energy → Electrical energy.
AP SSC DISTINCTION: MOTOR uses electricity to produce motion (electric fan, pump, mixer). GENERATOR uses motion to produce electricity (power station turbine, bicycle dynamo). TRANSFORMER: Changes voltage without changing frequency. Step-up: more turns in secondary → higher voltage. Step-down: fewer turns → lower voltage. V₁/V₂ = N₁/N₂. AP SSC sometimes tests transformer calculations.
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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT
Confusing Fleming's Left-Hand Rule (motor) and Right-Hand Rule (generator)
EASY MEMORY: LEFT hand → MOTOR (uses electricity → does work). RIGHT hand → GENERATOR (does mechanical work → makes electricity). In BOTH rules: FIRST finger = Field. MIDDLE finger = Current (or induced Current). THUMB = Motion. For motors: force (thumb) depends on current and field. For generators: induced current (middle finger) results from motion and field. 'Left for Motor, Right for Generator' — Left = power IN (motor takes power), Right = power OUT (generator gives power).

Practice problems

Work through this chapter's problems as a readiness check — reveal each solution, mark yourself honestly, and get your gap report at the end.

Readiness check

Are you exam-ready for Electromagnetism?

1 problems from this chapter. Try each one, reveal the worked solution, mark yourself honestly — get your gap report at the end.

1 questions~2 min

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

  • Magnetic field around a straight current-carrying conductor: circular field lines around the wire. Direction by RIGHT-HAND THUMB RULE: thumb points in current direction → curled fingers show field direction.
  • Magnetic field inside a solenoid: uniform, parallel field lines — like a bar magnet. Right-hand rule for solenoid: curl fingers in current direction → thumb points to North pole.
  • FORCE on a current-carrying conductor in a magnetic field: F = BIL sinθ. Maximum when current ⊥ field (θ=90°). Zero when current ∥ field (θ=0°).
  • Fleming's LEFT-HAND RULE (for motor): thumb = Force (motion), index finger = Field, middle finger = Current. Gives direction of force on conductor → motor (electrical → mechanical).
  • Fleming's RIGHT-HAND RULE (for generator): thumb = Motion of conductor, index finger = Field, middle finger = induced Current. Gives direction of induced current → generator (mechanical → electrical).
  • ELECTRIC MOTOR: converts electrical energy to mechanical energy. Principle: force on current-carrying conductor in magnetic field (Lorentz force).
  • ELECTRIC GENERATOR: converts mechanical energy to electrical energy. Principle: Faraday's Law of electromagnetic induction.
  • FARADAY'S LAW: induced EMF is proportional to the rate of change of magnetic flux. EMF = −ΔΦ/Δt. More turns in coil = more EMF.
  • AC generator: armature rotates in magnetic field → flux changes continuously → alternating EMF produced. DC generator: uses commutator to produce unidirectional current.
  • TRANSFORMER: uses mutual induction. Step-up: more turns in secondary → higher voltage. Step-down: fewer turns in secondary → lower voltage. Principle: V₁/V₂ = N₁/N₂.

Andhra Pradesh (BIEAP) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Electric vehicles and regenerative braking

EVs (like APSRTC's electric buses in Andhra Pradesh) use the same motor-generator duality from this chapter. When accelerating, the motor converts battery energy to motion. When braking, the motor acts as a generator, converting kinetic energy back to electricity and recharging the battery. This regenerative braking is why EVs are more efficient in city traffic than on highways — more braking = more energy recovered.

Power generation at scale

Every power plant (thermal, hydroelectric, nuclear, wind) converts some form of mechanical energy into electrical energy using generators built on Faraday's Law. At the Srisailam hydroelectric project (on the Krishna river, one of the largest in AP), water flow spins turbine blades → turbine rotates the generator coil in a magnetic field → induced EMF → electricity. The physics is exactly the generator principle from this chapter.

Induction cooktops and wireless charging

Induction cooktops heat food without a flame — they use electromagnetic induction (alternating magnetic field from a coil) to induce eddy currents in the iron/steel pot, which heat the pot via I²R. Wireless phone chargers use the same transformer-like mutual induction. These technologies — increasingly common in Indian urban homes — are direct applications of Faraday's Law.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

1
Fleming's rules: practice demonstrating them with your actual hand. In the exam, position your hand mentally and trace which finger points which way. Always specify: Left-hand = Motor (Force, Field, Current). Right-hand = Generator (Motion, Field, induced Current).
2
Generator working: write in 4 steps — (1) Faraday's Law as principle, (2) Structure (rectangular coil between poles of a magnet), (3) Rotation of coil → changing flux, (4) Induced EMF → current in external circuit.
3
Motor working: write in 4 steps — (1) Force on current-carrying conductor in magnetic field (Lorentz force), (2) Structure (rectangular coil + commutator), (3) Force on two sides of coil in opposite directions → torque → rotation, (4) Commutator reverses current every half turn → continuous rotation.
4
Distinguish electromagnetic induction from Lenz's law: Faraday gives the MAGNITUDE of induced EMF. Lenz's law gives the DIRECTION — the induced current opposes the change in flux that caused it.
5
For 2-mark applications: always identify the device (motor, generator, transformer, electromagnet) and state the principle it uses. 'The electric bell uses an electromagnet' is 1 mark; explaining how the electromagnet creates the ringing mechanism is the second mark.

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

STRETCH
Investigate the discovery of electromagnetic induction by Michael Faraday (1831) and independently by Joseph Henry — Faraday published first. Research Faraday's original experiment: pushing a bar magnet into a coil of wire → galvanometer deflects. What he observed is today encoded in Faraday's Law and Lenz's Law.
STRETCH
Research Lenz's Law in detail — the induced current always opposes the change in flux. This is an expression of energy conservation: if the induced current aided the change, it would amplify itself indefinitely (violating conservation of energy). Lenz's law explains why pulling a magnet out of a coil requires effort — the induced current creates a magnetic field that attracts the magnet back.
STRETCH
Explore three-phase AC generators — the standard for power generation worldwide. Three coils arranged 120° apart generate three sinusoidal waveforms offset by 120°. Three-phase power can deliver smooth, constant power (the three phases sum to a constant value) and allows more efficient motors.
STRETCH
Research the Tesla coil — an air-core resonant transformer that produces extremely high voltages at high frequencies, creating dramatic electrical arcs. Nikola Tesla (after whom the EV company is named) envisioned wireless power transmission using resonant induction — a concept now partially realised in wireless charging (though at much lower power).

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

AP Board SSC (Class 10)High — generator/motor working principle and Fleming's rules are standard 4+2 mark questions
JEE Main / Advanced (Physics)Very High — Electromagnetic Induction and Alternating Current are two separate high-weight chapters in Class 12 Physics
AP EAMCET (Engineering)High — electromagnetic induction, motors, and generators are tested in Class 12 Physics section of EAMCET
NTSE (Science section)Moderate — Fleming's rules and basic electromagnet/motor/generator concepts appear in NTSE science

Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

MOTOR needs CURRENT to work → Left hand (L for Left, L for Load — the motor is a load). GENERATOR produces CURRENT → Right hand (Right for Result — current is the result). Alternative: MOTOR = LEFT = LORENTZ force (F, B, I). GENERATOR = RIGHT = faraday's law (motion, B, induced I). In the exam, always specify which rule you are applying and what each finger represents before using it.

As the armature rotates, the current from the external circuit needs to reverse direction in the armature every half turn — otherwise the torque would reverse and the motor would oscillate rather than spin continuously. The split-ring commutator (two C-shaped metal rings with a gap) switches the connections to the armature every half turn, ensuring the current in the armature always flows in the same direction relative to the magnetic field. This maintains a torque in the same rotational direction, allowing continuous rotation.

Electromagnetic induction (Faraday's Law) underlies: (1) The electric generator — mechanical rotation of coil in magnetic field → changing flux → induced EMF → current. (2) The transformer — AC current in primary coil creates changing magnetic field → induces EMF in secondary coil. (3) Induction cooktops — alternating current in a coil under the cooktop creates a rapidly changing magnetic field → induces eddy currents in the metal pot → pot heats up due to I²R. (4) Inductive phone chargers — same principle as transformer, but wirelessly.

A transformer works on Faraday's Law: EMF is induced only when magnetic flux is CHANGING (ΔΦ/Δt). Alternating current continuously changes direction → continuously changing magnetic field → continuously changing flux → continuous induction in the secondary coil. Direct current is constant → produces a constant magnetic field → no change in flux → no induction. If you connect DC to a transformer primary, you only get an induced pulse momentarily when the DC is switched on or off. This is why household current is AC — DC cannot be easily transformed to different voltages.

A motor and a generator are physically the SAME DEVICE — a coil of wire that can rotate in a magnetic field. The difference is energy direction: if you supply current to the coil, it rotates (motor — electrical → mechanical). If you mechanically rotate the coil, it generates current (generator — mechanical → electrical). In fact, electric vehicles use the same motor as a generator when braking (regenerative braking) — converting kinetic energy back to electrical energy stored in the battery.
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Last reviewed on 28 May 2026. Written and reviewed by subject-matter experts — read about our process.
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