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Rajasthan (RBSE)Class 10 Science★ 6–8 marks · RBSE Class 10 Science board (Unit — Effects of Current)

Magnetic Effects of Electric Current

Oersted's discovery that a current bends a compass needle launched the electric age. RBSE Class 10 Science Chapter 12 — magnetic field and field lines, the field due to a straight wire, loop and solenoid, the right-hand and Fleming's left-hand rules, force on a current-carrying conductor, the electric motor, electromagnetic induction & Fleming's right-hand rule, the generator, and household circuits & safety — with RBSE board-pattern questions and solutions.

⏱ 38 min readMedium difficulty✓ Free · NCERT-aligned

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

1Draw and interpret magnetic field lines and state their properties
2Determine the field direction around a straight wire, loop and solenoid using the right-hand thumb rule
3Apply Fleming's left-hand rule to find the force on a current-carrying conductor and explain the electric motor
4Explain electromagnetic induction and use Fleming's right-hand rule for the induced current
5Distinguish an AC generator (slip rings) from a DC generator (split-ring commutator), and recall the 50 Hz Indian supply
6Identify the live, neutral and earth wires and explain overloading, short-circuiting, fuses and earthing

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Why this chapter matters

This chapter unifies electricity and magnetism and explains the two machines that run the modern world — the motor and the generator. In the RBSE board it reliably yields a rule-based or diagram question (motor, generator, or household wiring) plus a short conceptual question on field patterns or safety.

Before you start — revise these

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

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Electricity (Class 10)

Current, circuits, the heating effect and the safety fuse.

Magnetic Effects of Electric Current — RBSE Class 10 (Science)

In 1820, Hans Christian Oersted noticed that a compass needle near a current-carrying wire twitched the moment he switched the current on. A tiny twitch — and the entire modern world of motors, generators and power grids unfolded from it. Electricity and magnetism, it turned out, are two faces of one coin. This chapter shows you both faces.

1. Magnetic field and field lines

A magnet has two poles and exerts forces; the region around it where this force acts is its magnetic field — a quantity with both magnitude and direction. We picture it with magnetic field lines:

They run from north to south outside the magnet (and S→N inside).
They never cross (if they did, a compass would point two ways at once).
Closer lines = stronger field. Where lines are crowded, the field is strong.
A compass needle aligns itself along the field line at any point.

2. Magnetic field due to a current

A straight current-carrying conductor

The field forms concentric circles around the wire. Its direction is given by the Right-Hand Thumb Rule:

Grip the wire with your right hand, thumb pointing along the current; your curled fingers point along the magnetic field.

The field is stronger near the wire and when the current is larger.

A circular loop

Each point of the loop contributes circular field lines; at the centre they add up to give a field roughly perpendicular to the loop's plane. More turns ⇒ the fields add ⇒ stronger field at the centre.

A solenoid

A solenoid is a long coil of many turns. Its field pattern is just like a bar magnet — uniform field inside, with a clear north and south end. Putting a soft-iron core inside makes an electromagnet (strong, and switchable on/off).

3. Force on a current-carrying conductor — Fleming's Left-Hand Rule

A current-carrying wire placed in a magnetic field experiences a force. The force is largest when the current and field are perpendicular. Its direction is given by Fleming's Left-Hand Rule:

Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular. Forefinger → Field, Middle finger → Current, Thumb → Thrust (force/motion).

This force is the principle behind the electric motor.

The electric motor

A motor converts electrical energy into mechanical energy. A current-carrying rectangular coil in a magnetic field feels equal and opposite forces on its two sides, which make it rotate. A split-ring commutator reverses the current in the coil every half-turn so the rotation continues in the same direction. Motors run fans, pumps, mixers, washing machines and more.

4. Electromagnetic induction — Fleming's Right-Hand Rule

The reverse of the motor: move a conductor through a magnetic field (or change the field through a coil) and a current is induced. This is electromagnetic induction, discovered by Michael Faraday.

A current is induced when:

a conductor moves across a magnetic field, or
the magnetic field through a coil changes (e.g., a magnet pushed in/out of a coil — a galvanometer needle deflects).

The direction of the induced current is given by Fleming's Right-Hand Rule (same finger assignment, but the right hand): Forefinger → Field, Thumb → motion, Middle finger → induced Current.

The electric generator

A generator converts mechanical energy into electrical energy — induction run in reverse of a motor. A coil rotated in a magnetic field induces a current.

An AC generator uses slip rings → gives alternating current (the current reverses every half rotation). In India, AC reverses 50 times per second (50 Hz).
A DC generator uses a split-ring commutator → gives direct current.

5. Domestic electric circuits and safety

Power reaches homes through three wires:

Live (red/brown) — at 220 V.
Neutral (black/blue) — at 0 V.
Earth (green) — connected to a metal plate in the ground; a safety wire that carries leakage current away and gives the body of metal appliances a safe path, preventing fatal shocks.

The potential difference between live and neutral is 220 V in India.

Overloading happens when too many appliances draw current together; short-circuiting happens when live and neutral wires touch directly (resistance ≈ 0, current shoots up). Both cause dangerous heating. Protection: a fuse or MCB in the live wire melts/trips and breaks the circuit. Earthing protects against shock from leaking appliances.

6. Closing thought

Two rules, two machines, one big idea:

Current → magnetism (Oersted): a current makes a field; a field exerts a force on a current → the motor (Fleming's Left hand).
Magnetism → current (Faraday): a changing field induces a current → the generator (Fleming's Right hand).

Every power station turns a generator; every fan, pump and EV runs a motor. The same coil, the same magnet — just run forwards or backwards. Keep the two Fleming rules straight (Left for the motor's force, Right for the induced current), learn the three household wires and the role of the fuse and earth, and this chapter is comfortably scored.

Key formulas & results

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

Right-Hand Thumb Rule

Thumb → current, curled fingers → magnetic field

Field direction around a straight current-carrying wire.

Fleming's Left-Hand Rule

Fore→Field, Middle→Current, Thumb→Force/motion

Force on a conductor → the electric MOTOR.

Fleming's Right-Hand Rule

Fore→Field, Thumb→motion, Middle→induced Current

Induced current → the electric GENERATOR.

Solenoid field

Field pattern = bar magnet; iron core → electromagnet

Uniform field inside; switchable strength.

Indian AC supply

f = 50 Hz, V = 220 V (live–neutral)

AC reverses direction 50 times per second.

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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

✗ Using the same hand for the motor and the generator

✓ LEFT hand for the force on a current (motor); RIGHT hand for the induced current (generator). Mnemonic: moto'R'... no — remember 'Left = force, Right = induced'.

WATCH OUT

✗ Saying magnetic field lines can cross

✓ Field lines NEVER cross. If they did, a compass at that point would have to point in two directions at once, which is impossible.

WATCH OUT

✗ Confusing the split-ring (commutator) with slip rings

✓ Split-ring commutator → reverses current → used in DC motor/DC generator. Slip rings → do not reverse → used in AC generator.

WATCH OUT

✗ Mixing up the function of the earth wire and the neutral wire

✓ Neutral completes the circuit at ~0 V. Earth is a SAFETY wire to ground; it carries leakage current away and prevents shocks from the metal body of an appliance.

WATCH OUT

✗ Saying a steady magnet near a coil induces current

✓ Induction needs a CHANGE — the magnet/coil must move or the field must change. A stationary magnet induces no current.

WATCH OUT

✗ Calling an electromagnet a permanent magnet

✓ An electromagnet works only while current flows; switch it off and the magnetism (mostly) disappears — that is its advantage.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

In-text Q (Field & field lines)

Properties of field lines; compass; field of a bar magnet

Questions

In-text Q (Field due to current)

Straight wire, loop, solenoid; right-hand thumb rule

Questions

In-text Q (Force & motor)

Fleming's left-hand rule; electric motor

Questions

In-text Q (Induction & generator)

Electromagnetic induction; AC/DC generator; domestic circuits

Questions

End-of-chapter Ex

End-of-chapter exercise

Mixed rule-based, diagram and conceptual questions

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Field lines

Why do two magnetic field lines never intersect each other?

▶ Show solution

If two lines crossed, the compass at that point would have to point in two directions at once — impossible. So field lines never intersect.

✦ Answer: Because the field can have only one direction at a point.

Q2EASY· Discovery

Whose experiment first showed that an electric current produces a magnetic effect?

▶ Show solution

✦ Answer: Hans Christian Oersted (1820) — a current deflected a nearby compass needle.

Q3EASY· Solenoid

The magnetic field pattern of a current-carrying solenoid resembles that of which familiar magnet?

▶ Show solution

✦ Answer: A bar magnet (with a north and a south end and a uniform field inside).

Q4MEDIUM· Rules

State Fleming's left-hand rule and name the device based on it.

▶ Show solution

Step 1 — Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular.

Step 2 — Forefinger → magnetic Field, Middle finger → Current, Thumb → Force (motion).

Step 3 — Device: the electric motor.

✦ Answer: rule as above; based on it → electric motor.

Q5MEDIUM· Right-hand thumb

Using the right-hand thumb rule, describe the magnetic field produced around a straight current-carrying wire.

▶ Show solution

Step 1 — Grip the wire in the right hand with the thumb along the current direction.

Step 2 — The curled fingers show the field, which forms concentric circles around the wire.

Step 3 — The field is stronger near the wire and for larger current.

✦ Answer: concentric circular field lines around the wire; direction by the curl of the right-hand fingers.

Q6MEDIUM· Electromagnet

What is an electromagnet? Give one advantage over a permanent magnet.

▶ Show solution

Step 1 — An electromagnet is a solenoid with a soft-iron core that becomes magnetic only when current flows through it.

Step 2 — Advantage: it can be switched on and off, and its strength can be controlled by changing the current/turns.

✦ Answer: a current-controlled magnet; advantage = switchable and adjustable strength.

Q7HARD· Electric motor

Explain the working of an electric motor and state the function of the split-ring commutator.

▶ Show solution

Step 1 — A current-carrying coil is placed in a magnetic field.

Step 2 — By Fleming's left-hand rule, the two sides of the coil experience equal and opposite forces, producing a turning effect (torque) that rotates the coil.

Step 3 — After each half rotation the split-ring commutator reverses the current direction in the coil, so the force keeps acting in the same rotational sense and the coil continues to spin one way.

✦ Answer: forces on the coil sides rotate it; the commutator reverses current every half-turn to keep rotation continuous.

Q8HARD· Induction

State the conditions under which a current is induced in a coil, and name the rule for the direction of the induced current.

▶ Show solution

Step 1 — A current is induced when the magnetic field linked with the coil CHANGES — by moving a magnet in/out of the coil, or moving the coil in a field, or changing the current in a nearby coil.

Step 2 — The direction of the induced current is found by Fleming's right-hand rule (Forefinger→Field, Thumb→motion, Middle→induced Current).

✦ Answer: a changing magnetic flux induces current; direction by Fleming's right-hand rule.

Q9HARD· Generator

Differentiate between an AC generator and a DC generator. Why is AC preferred for transmission, and what is the frequency of AC in India?

▶ Show solution

Step 1 — AC generator uses slip rings → output current reverses direction periodically (alternating current). DC generator uses a split-ring commutator → output is unidirectional (direct current).

Step 2 — AC is preferred for transmission because its voltage can be easily stepped up (to reduce current and hence I²R losses) and stepped down using transformers.

Step 3 — In India, AC has a frequency of 50 Hz (it reverses 50 times per second).

✦ Answer: slip rings (AC) vs commutator (DC); AC transmits efficiently via transformers; 50 Hz in India.

Q10HARD· Household safety

Name the three wires in a domestic circuit and their colours. Explain the difference between overloading and short-circuiting, and how a fuse protects the circuit.

▶ Show solution

Step 1 — Live (red/brown, ~220 V), Neutral (black/blue, ~0 V), Earth (green, safety wire to ground).

Step 2 — Overloading: too many appliances draw a large total current. Short-circuiting: live and neutral touch directly so resistance ≈ 0 and the current becomes very large.

Step 3 — Both cause excessive heating (H = I²Rt). A fuse (a thin, low-melting wire in the live wire) melts when the current exceeds a safe value, breaking the circuit and preventing fire/damage.

✦ Answer: live/neutral/earth with colours; overload = too much load, short circuit = live–neutral contact; fuse melts to break the circuit.

5-minute revision

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

•Field lines: N→S outside, never cross, closer = stronger; compass aligns along them.
•Right-hand thumb rule → field around a straight wire (concentric circles).
•Solenoid field = bar magnet; soft-iron core → switchable electromagnet.
•Fleming's LEFT-hand rule → force on a current → electric MOTOR (commutator reverses current each half-turn).
•Electromagnetic induction (Faraday): a CHANGING field induces current; direction by Fleming's RIGHT-hand rule.
•Generator: mechanical → electrical. AC generator = slip rings; DC generator = split-ring commutator. India: 50 Hz.
•Domestic wires: live (220 V), neutral (0 V), earth (safety). PD between live and neutral = 220 V.
•Overloading (too much current) and short-circuiting (live–neutral contact) cause heating; fuse/MCB and earthing protect.

Rajasthan (RBSE) marks blueprint

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

Typical chapter weightage: 6–8 marks

Question type	Marks each	Typical count	What it tests
MCQ / Assertion–Reason	1	1–2	Field-line properties, Oersted, solenoid, 50 Hz
Short answer	2	1–2	State a rule; describe a field pattern; electromagnet
Short answer	3	1	Working of the motor; conditions for induction
Long / diagram-based	4–5	1	Generator (AC vs DC) or domestic circuit & safety

Prep strategy

Learn the three Fleming/right-hand rules with their exact finger assignments and one device each
Practise drawing field lines for a bar magnet, straight wire, loop and solenoid
Memorise the motor and generator working as 4–5 line answers with the role of commutator/slip rings
Lock in the three household wires, their colours, and the roles of fuse and earth

Where this shows up in the real world

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

Every fan and pump

Electric motors based on Fleming's left-hand rule run ceiling fans, water pumps, mixers and washing machines.

Power stations

Generators convert the mechanical energy of turbines (water, steam, wind) into the AC electricity that lights your home.

Electromagnets in cranes

Switchable electromagnets lift and drop heavy iron scrap in junkyards and steel plants.

Transformers on poles

Step-down transformers on the street use electromagnetic induction to bring 11 kV lines down to a safe 220 V.

MCBs and earthing at home

The MCB box and three-pin earthed plugs protect your family from short circuits and shocks.

Electric vehicles

EVs use powerful electric motors for drive and regenerative braking that runs the motor as a generator to recharge the battery.

Exam strategy

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

When a rule is asked, state the finger assignments precisely AND name the device it explains.
For motor/generator answers, mention the role of the commutator or slip rings — it is a marked point.
Draw neat, labelled field-line diagrams; show direction with arrows.
Distinguish AC and DC generators in a two-column format for clarity.
For household-circuit questions, give wire colours, voltages and the safety role of fuse and earth.
Always note that induction needs a CHANGE in the magnetic field — a static magnet induces nothing.

Going beyond the textbook

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

The quantitative force law F = BIL and the torque on a current loop in a uniform field.
Faraday's and Lenz's laws: the induced EMF equals the rate of change of flux, opposing the change.
How transformers work and why they only operate on AC, not DC.
The magnetic force on a moving charge, F = qvB, and circular motion of charges in a field.

Where else this chapter is tested

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

RBSE Class 10 Board (BSER Ajmer)High — a rule/diagram or generator/household-circuit question each year

NTSE / state scholarshipMedium — field lines and rules MCQs

JEE FoundationHigh — leads into Class 12 magnetism and EM induction

Science Olympiad (NSO)Medium — conceptual field and rule questions

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Questions students ask

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

Yes. RBSE prescribes the NCERT Science textbook for Class 10, so the chapter and exercises are identical. RBSE (BSER Ajmer) only sets the exam pattern and marking.

LEFT hand → the force on a current → the MOTOR. RIGHT hand → the induced current → the GENERATOR. Tie it to 'a motor takes current and gives motion (left), a generator takes motion and gives current (right)'.

A split-ring commutator reverses the current direction every half rotation — it is used in DC motors and DC generators. Slip rings do not reverse the current and are used in AC generators to deliver alternating current.

The earth wire is a safety device. If the live wire accidentally touches the metal body of an appliance, the earth wire carries the leakage current safely to the ground instead of through the user, preventing a fatal shock.

AC voltage can be easily stepped up and down using transformers. Transmitting at high voltage keeps the current low, which minimises the I²R heating losses in long power lines. India transmits AC at 50 Hz.

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