Is it correct to say: Using Fleming's LEFT-hand rule for a generator?

LEFT hand for motor (force on conductor); RIGHT hand for generator (induced current). Mnemonic: 'GRe-Right'.

Is it correct to say: Assuming AC and DC give the same heating for the same peak voltage?

AC uses RMS values. For India's 220 V AC, RMS ≈ 220 V but peak V ≈ 311 V.

Is it correct to say: Drawing an electric motor's split-ring commutator as a full ring (like a generator's slip ring)?

DC motor uses a SPLIT ring commutator (2 half-rings). AC generator uses SLIP rings (2 full rings).

Is it correct to say: Confusing north/south poles of a solenoid?

Look at one end; if current appears anti-clockwise, that end is N; clockwise ⇒ S. (Clock rule.)

Is it correct to say: Writing that a straight wire experiences a force even when placed along the field?

F = BIL sinθ. If I is parallel (θ = 0°) or anti-parallel (θ = 180°) to B, force is ZERO.

Is it correct to say: Not connecting the earth wire in a domestic circuit?

Earth wire (green/yellow) safely grounds any leakage current from the metal body — prevents electric shock.

Magnetic Effects of Electric Current

Magnetic field due to a current, force on a current-carrying conductor, electromagnetic induction, motor and generator — NCERT Class 10 Physics Ch 13

📐 9 formulas✏️ 3 examples🎯 6 practice⚖️ 5-6 marks🏫 CBSE📚 Class 10✓ 2025–26 syllabus

💡

Board Exam Tips

→Right-hand thumb rule for a straight conductor and clock rule for a solenoid — draw AND label.
→Fleming's LEFT-hand rule → force on a conductor (motor). Fleming's RIGHT-hand rule → induced current (generator). Do NOT swap.
→AC vs DC — a 2-mark question every year. Frequency of AC in India = 50 Hz.
→Domestic wiring: LIVE red, NEUTRAL black (older) / brown-blue (newer). Earth wire — green/yellow — for safety.
→State the working of an electric motor with a labelled diagram — full 5-mark answer at least once in your revision.

📊 Diagram

Current-carrying solenoid producing a magnetic field similar to a bar magnet

📐 Formulas(9)

Magnetic Field of a Straight Conductor

B \propto \frac{I}{r}

Symbol	Meaning
$B$	Magnetic field (tesla, T)
$I$	Current in the wire (A)
$r$	Perpendicular distance from wire (m)

Right-hand Thumb Rule

B direction ⊥ I

Magnetic Field of a Circular Loop

B \propto \frac{I}{r}

Magnetic Field of a Solenoid★ Board fav

B = μ_{0} n I

Symbol	Meaning
$μ_{0}$	Permeability of free space = 4π × 10⁻⁷ T·m/A
$n$	Number of turns per metre (m⁻¹)
$I$	Current in the solenoid (A)

Force on a Current-carrying Conductor★ Board fav

F = B I L

Fleming's Left-hand Rule

Thumb = F, Fore = B, Middle = I

Fleming's Right-hand Rule★ Board fav

Thumb = v, Fore = B, Middle = I_{in d}

Faraday's Law (qualitative)

ε \propto \frac{ΔΦ}{Δ t}

Electric Power (Household)

P = V I

✏️ Solved Examples

1Solved Exampleeasy3 steps

A wire carrying 5 A of current is placed perpendicular to a magnetic field of 0.2 T. If the length of the wire in the field is 0.4 m, find the force on it.

List given values

I = 5 A, B = 0.2 T, L = 0.4 m

2Solved Exampleboard4 steps

State the principle of an electric motor. Draw a labelled diagram and explain its working in brief.

Principle: a current-carrying rectangular coil placed in a magnetic field experiences a couple (torque) that rotates it — direction of force on each side given by Fleming's LEFT-hand rule.

3Solved ExampleHOTS5 steps

In an AC generator, the coil rotates at 50 revolutions per second in a uniform field of 0.5 T. It has 200 turns and area 100 cm². Compare its peak EMF with a hypothetical arrangement where the frequency is doubled. (Take ε_max ∝ NBAω.)

Peak EMF depends on ω = 2π f

ε_{ma x} = N B A ω = N B A (2 π f)

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Using Fleming's LEFT-hand rule for a generator
✓LEFT hand for motor (force on conductor); RIGHT hand for generator (induced current). Mnemonic: 'GRe-Right'.
2
Assuming AC and DC give the same heating for the same peak voltage
✓AC uses RMS values. For India's 220 V AC, RMS ≈ 220 V but peak V ≈ 311 V.
3
Drawing an electric motor's split-ring commutator as a full ring (like a generator's slip ring)
✓DC motor uses a SPLIT ring commutator (2 half-rings). AC generator uses SLIP rings (2 full rings).
4
Confusing north/south poles of a solenoid
✓Look at one end; if current appears anti-clockwise, that end is N; clockwise ⇒ S. (Clock rule.)
5
Writing that a straight wire experiences a force even when placed along the field
✓F = BIL sinθ. If I is parallel (θ = 0°) or anti-parallel (θ = 180°) to B, force is ZERO.
6
Not connecting the earth wire in a domestic circuit
✓Earth wire (green/yellow) safely grounds any leakage current from the metal body — prevents electric shock.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
State the direction of the magnetic field around a straight wire in which current flows vertically upwards.
Q2
A 20 cm long conductor carries a current of 2 A perpendicular to a magnetic field of 0.5 T. Find the force experienced.
Q3
What is the frequency of AC in India, and how many times does the current change direction in one second?
Q4
Name one device based on the heating effect of current and one based on the magnetic effect.
Q5
Give two differences between AC and DC generators.
Q6
Why is the tungsten used for an electric bulb but nichrome for a heater?

📝 Notes

Magnetic Effects of Electric Current

Every current-carrying conductor produces a magnetic field around it — the foundation of motors, generators, transformers and MRI machines.

Two fundamental discoveries

Oersted (1820): a compass placed near a current-carrying wire deflects — current creates a magnetic field.
Faraday (1831): a changing magnetic field induces an EMF in a coil — basis of the generator.

Field patterns to memorise

Straight wire: concentric circles around the wire.
Circular loop: field lines pass through the loop along its axis (like a tiny bar magnet).
Solenoid: uniform field inside; outside pattern identical to a bar magnet.

Motor vs generator — one-line difference

Motor: electrical → mechanical energy (uses Fleming's LEFT-hand rule, needs split-ring commutator for DC).
Generator: mechanical → electrical energy (uses Fleming's RIGHT-hand rule; AC generator uses slip rings, DC uses a commutator).

Domestic wiring safety essentials

Live wire (red / brown): carries current from mains.
Neutral (black / blue): completes the circuit at ~0 V.
Earth (green / yellow): connected to the metal body of appliances; safely conducts leakage to the ground.
Fuse / MCB: breaks the circuit if current exceeds rated value (short circuit or overload).