PhysicsICSE Class 10 · Magnetic Effect of Current and Electromagnetic Induction

Electromagnetic Induction: Induced Current, Fleming's Right-Hand Rule and the AC Generator (ICSE Class 10)

Updated 16 October 2026 · Fact-checked

Electromagnetic induction is the production of an emf, and so a current, in a conductor when the magnetic field through it changes, for example when a magnet moves into a coil. The current is larger for faster change, more turns and a stronger magnet. Its direction always opposes the change and is given by Fleming's right-hand rule.

Pushing the N pole in makes the coil face N (repels); pulling it out makes it S (attracts) – the induced current always opposes the change.

Illustration drawn for QuestionBuddy.

Understand Electromagnetic Induction and the AC Generator

The basic observation. Connect a coil to a galvanometer (no cell) and move a bar magnet:

Action	Galvanometer
Push the N pole into the coil	Deflects one way
Hold the magnet still inside	No deflection
Pull the N pole out	Deflects the other way
Push in faster	Larger deflection
Keep the magnet still and move the coil	Same effects: only relative motion matters

A current flows only while the magnetic field through the coil is changing. This is electromagnetic induction: the changing field induces an emf, which drives an induced current if the circuit is closed. The same happens when the current in a nearby coil is switched on or off, or is alternating, because its magnetic field changes.

Factors affecting the size of the induced current (emf).

Speed of the change (faster motion of magnet or coil).
Number of turns in the coil.
Strength of the magnet (magnetic field).
For a rotating coil: also its area and speed of rotation.

Direction: Lenz's law. The induced current always flows in a direction that opposes the change producing it.

N pole approaching a coil: the near face of the coil becomes an N pole, repelling it.
N pole moving away: the near face becomes an S pole, attracting it back.

Use the clock rule to turn a pole into a current direction: looking at a face, anticlockwise current makes it N; clockwise makes it S. The direction you report depends on the side you look from.

Because the induced current always opposes the motion, work must be done to move the magnet; this mechanical work is what becomes electrical energy. Energy is conserved.

Fleming's right-hand rule (for a straight conductor moving across a field). Stretch the thumb, forefinger and middle finger of the right hand mutually at right angles:

Forefinger: direction of the field (N to S);
Thumb: direction of motion of the conductor;
Middle finger: direction of the induced current.

No current is induced if the conductor moves parallel to the field lines (it does not cut them). Compare: the left-hand rule is for the motor effect (force on a current); the right-hand rule is for the generator effect (induced current).

The AC generator (main parts and energy transfer; working not required). It converts mechanical energy into electrical energy.

Armature coil: a rectangular coil of many turns, rotated by an external agent (a turbine, an engine or a hand crank).
Field magnet: provides a strong magnetic field.
Slip rings: two separate rings, one joined to each end of the coil, turning with it.
Carbon brushes: press against the slip rings and connect the coil to the external circuit.

As the coil rotates, its sides cut the field first one way and then the other, so the output current reverses direction every half turn: alternating current. For a simple generator with one coil between two poles, the frequency equals the number of rotations per second.

Household AC. In India the supply is 220 V, 50 Hz: 50 complete cycles per second, so the current reverses direction 100 times a second, and one cycle takes $\frac{1}{50} = 0.02$ s.

Advantages of AC over DC.

AC voltage can be easily stepped up or down by transformers.
It can therefore be transmitted over long distances at high voltage with less energy loss.
AC generators are simpler and cheaper to build and maintain for large-scale generation.

Electromagnetic Induction and the AC Generator: formulas and key facts

Fleming's right-hand rule: Forefinger field
Thumb motion
Middle finger induced current; Generator effect.
Factors for induced emf: Faster change
More turns
Stronger field
Larger coil area (rotating coil); Each increases the induced current.
Household AC (India): $f = 50 Hz, T = \frac{1}{f} = 0.02 s$; Direction reverses 100 times per second.
Lenz's law: Induced current opposes the change producing it; Approaching N meets N; receding N meets S.

Forefinger	field
Thumb	motion
Middle finger	induced current

How to solve Electromagnetic Induction and the AC Generator questions

Direction questions need a fixed procedure: decide the pole the coil must form, then convert it to a current direction for the stated observer.

1Ask what is changing: is the magnet (or coil) approaching or receding, or is a current switched on or off?
2Apply Lenz's law: an approaching pole meets a like pole; a receding pole meets an unlike pole.
3Use the clock rule from the observer's side: N face means anticlockwise, S face means clockwise.
4For a straight rod in a field, use Fleming's right-hand rule with the field from N to S.
5For size questions, list the factors: speed of change, number of turns, field strength (and area for a rotating coil).

Electromagnetic Induction and the AC Generator in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Why a dynamo gets harder to pedal

Suppose you switch on the dynamo-powered lamp of a bicycle and notice that pedalling feels slightly harder.

Explain this using electromagnetic induction.

Try it first, then show the solutionSolution

The dynamo's rotating magnet induces a current in its coil, which lights the lamp.
By Lenz's law, the induced current opposes the rotation that produces it.
So you must do extra work, which becomes the electrical energy (and then light) of the lamp.

Answer: The induced current opposes the motion, so extra work is needed: that work is the lamp's energy.

Memory hook: No free light: you pay in pedalling.

Wireless charging

Imagine placing your phone on a wireless charging pad. There is no plug, but the battery charges.

How can energy reach the phone without wires?

Try it first, then show the solutionSolution

A coil in the pad carries alternating current, which makes a changing magnetic field.
A coil inside the phone sits in this changing field, so an emf is induced in it.
The induced current is used to charge the battery.

Answer: By electromagnetic induction between a coil in the pad and a coil in the phone.

Memory hook: Changing field, induced current.

Tricks to remember Electromagnetic Induction and the AC Generator

Short memory aids. Say each one aloud once, then use it on a question the same day.

Right for generators, left for motors
GeneRIGHTor: right hand for induced current. Motor: left hand for force.
Use it when: Choosing Fleming's rule.
FBI on the fingers
Thumb = motion, First finger = Field, seCond finger = Current.
Use it when: Fleming's right-hand rule.
Lenz is a spoilsport
Whatever you do, the induced current tries to undo it.
Use it when: Direction of induced current.
Slip for AC, split for DC motor
Slip rings let the AC slip out; the split ring keeps a DC motor turning one way.
Use it when: Generator versus motor parts.

Electromagnetic Induction and the AC Generator: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Which rule? · 1 mark · MCQBoard level

Fleming's right-hand rule is used to find the direction of:
(a) the force on a current-carrying conductor
(b) the magnetic field around a straight wire
(c) the induced current in a conductor moving in a magnetic field
(d) the poles of a solenoid

Try it first, then show the solutionSolution

The right-hand rule is the generator rule. (a) is the left-hand rule, (b) the right-hand thumb rule, (d) the clock rule.

Answer: (c) the induced current in a conductor moving in a magnetic field

Example 2: Defining induction · 3 marks · Short answerBoard level

(a) What is electromagnetic induction? (b) A magnet is pushed into a coil connected to a galvanometer. State two changes that would give a larger deflection. (c) What is observed if the magnet is kept at rest inside the coil?

Try it first, then show the solutionSolution

(a) The production of an emf (and current) in a conductor when the magnetic field linked with it changes. (1)
(b) Any two: push the magnet faster; use a stronger magnet; use a coil with more turns. (1)
(c) No deflection: the field through the coil is not changing. (1)

Answer: (a) emf induced by a changing field (b) Faster motion, stronger magnet, more turns (any two) (c) No deflection

Example 3: Generator parts · 3 marks · Short answerHarder board level

(a) State the energy conversion in an AC generator. (b) Name the parts that connect its rotating coil to the external circuit. (c) Why does its output alternate?

Try it first, then show the solutionSolution

(a) Mechanical energy → electrical energy. (1)
(b) Two slip rings (one at each end of the coil) and two carbon brushes pressing on them. (1)
(c) Each side of the coil moves first one way and then the other through the field, so the induced current reverses every half rotation. (1)

Answer: (a) Mechanical to electrical (b) Slip rings and carbon brushes (c) The current reverses every half turn

Example 4: Opposing the magnet · 4 marks · Long answerHarder board level

The N pole of a bar magnet is moved towards end A of a coil connected to a galvanometer. (a) What pole is formed at end A? (b) Seen from the magnet's side, is the current in the coil clockwise or anticlockwise? (c) What happens at A when the magnet is pulled away? (d) Why must work be done to move the magnet?

Try it first, then show the solutionSolution

(a) An N pole, to repel the approaching N pole (Lenz's law). (1)
(b) Anticlockwise (an N face carries anticlockwise current when viewed). (1)
(c) A becomes an S pole, attracting the receding magnet; the current reverses. (1)
(d) The induced current always opposes the motion, so work is done against this opposition; that work becomes electrical energy. (1)

Answer: (a) N (b) Anticlockwise (c) S pole; current reverses (d) Work against the opposing force becomes electrical energy

Example 5: Reading 50 Hz · 3 marks · Short answerHarder board level

The household supply in India is AC of frequency 50 Hz. (a) How long does one cycle take? (b) How many times per second does the current change direction? (c) At how many rotations per minute must a simple one-coil generator turn to produce this frequency?

Try it first, then show the solutionSolution

(a) $T = \frac{1}{50} = 0.02$ s. (1)
(b) Twice per cycle: $2 \times 50 = 100$ times. (1)
(c) 50 rotations per second $= 50 \times 60 = 3000$ rotations per minute. (1)

Answer: (a) 0.02 s (b) 100 times (c) 3000 rotations per minute

Example 6: A magnet falling through a ring · 3 marks · Short answerHOTS / competency

A bar magnet is dropped, S pole downwards, through a horizontal copper ring. For an observer looking down from above, state the direction of the induced current in the ring (a) as the magnet approaches the ring, (b) after it has passed through and is moving away below. (c) Will the magnet fall with an acceleration equal to, less than or more than $g$ ?

Try it first, then show the solutionSolution

(a) The approaching S pole is repelled, so the upper face of the ring becomes S: clockwise as seen from above. (1)
(b) Below the ring, the magnet's upper end (N) is moving away. The ring's lower face becomes S to attract it, so its upper face is N: anticlockwise as seen from above. (1)
(c) Less than $g$ : the induced currents oppose the motion both before and after. (1)

Answer: (a) Clockwise (b) Anticlockwise (c) Less than g

Example 7: Case study: a hand-cranked generator · 4 marks · Case-basedHOTS / competency

In a science fair, a student turns the handle of a small AC generator to light a bulb. The coil makes 5 rotations per second.
(a) Name the energy conversion and the parts that make the output alternating.
(b) Find the frequency of the output and the number of times per second the current reverses.
(c) Why does the handle become harder to turn when the bulb is connected?
(d) The student turns the handle faster. State two changes in the output.

Try it first, then show the solutionSolution

(a) Mechanical → electrical; the slip rings (with brushes) give an alternating output. (1)
(b) $f = 5$ Hz; the current reverses $2 \times 5 = 10$ times per second. (1)
(c) With the circuit closed, an induced current flows and, by Lenz's law, opposes the rotation, so more work is needed. (1)
(d) The induced emf (and current) becomes larger, so the bulb glows brighter, and the frequency increases. (1)

Answer: (a) Mechanical to electrical; slip rings (b) 5 Hz; 10 reversals per second (c) The induced current opposes rotation (d) Larger emf (brighter bulb) and higher frequency

Where students lose marks in Electromagnetic Induction and the AC Generator

The slips examiners see most often, and what to write instead.

Mistake: Ignoring the observer's side
Clockwise from one side is anticlockwise from the other.
Wrong working
Applying Lenz's law correctly but giving the direction as seen from below when the question says 'observer above'.
Right working
Decide the face's pole, then apply the clock rule from the stated viewpoint.
Do this: Draw an eye on your sketch at the observer's position.
Usually costs: Reported by CISCE examiners for 2025 Q1(xv).
Mistake: Generator factors mixed with motor factors
Induced current depends on speed of rotation, turns, area and field strength; 'current in the coil' is a motor factor.
Wrong working
'Induced current depends on the current through the coil.'
Right working
'Induced current depends on the speed of rotation, number of turns, area of the coil and field strength.'
Do this: Keep two separate lists: motor speed and generator output.
Usually costs: Reported by CISCE examiners for 2024 Q9(iii).
Mistake: Voltage given when frequency is asked
220 V is the voltage; 50 Hz is the frequency.
Wrong working
'Frequency of AC in India is 220 V.'
Right working
'50 Hz.'
Do this: Check the unit the question needs.
Usually costs: Reported by CISCE examiners for 2025 Q3(iii).
Mistake: 'Alternate current' or 'altering current'
The correct term is alternating current.
Wrong working
'Alternate current produces a varying field.'
Right working
'Alternating current (AC) produces a varying field.'
Do this: Use the full, correct technical term.
Usually costs: Reported by CISCE examiners for 2025 Q3(iii).

Exam tips

Name the rule precisely: Fleming's right-hand rule for induced current, left-hand rule for force.
In a Lenz's law answer, state the pole formed and why (to oppose approach or recession).
For a generator sketch, label armature coil, field magnet, slip rings and carbon brushes; write 'mechanical to electrical'.
Give exactly the number of factors asked for; extra wrong factors can cost marks.

Practice questions on Electromagnetic Induction and the AC Generator

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
In which case is NO current induced in a coil connected to a galvanometer?
(a) a magnet is pushed into the coil
(b) the coil is moved towards a fixed magnet
(c) a magnet is held at rest inside the coil
(d) a magnet is pulled out of the coil
Hint
Is the field changing?
Answer
(c) a magnet is held at rest inside the coil
Q2 · 1 mark · Very short answerBoard level
Name the rule used to find the direction of the current induced in a straight conductor moving across a magnetic field.
Hint
Generator effect.
Answer
Fleming's right-hand rule.
Q3 · 1 mark · Very short answerBoard level
How many times per second does the direction of the household AC in India reverse?
Hint
Two reversals per cycle at 50 Hz.
Answer
100 times.
Q4 · 2 marks · Short answerHarder board level
State Fleming's right-hand rule.
Hint
Three fingers of the right hand.
Answer
Stretch the thumb, forefinger and middle finger of the right hand mutually at right angles. If the forefinger points along the magnetic field and the thumb along the motion of the conductor, the middle finger gives the direction of the induced current.
Q5 · 3 marks · Short answerHarder board level
Explain how the use of transformers makes AC more economical than DC for sending electricity from a distant power station to a town.
Hint
Think of transformers.
Answer
Transformers work only with AC. With AC, the voltage can be stepped up at the power station, so the current in the long lines is small and the heating loss I²R is small; near the town it is stepped down to 220 V. DC cannot be stepped up this way, so it would need a large current and waste much more energy.
Q6 · 2 marks · Short answerHarder board level
The N pole of a magnet is pulled away from one end of a coil. What polarity does that end of the coil acquire? Explain.
Hint
Oppose the change.
Answer
An S pole. By Lenz's law the induced current opposes the change; the magnet is moving away, so the coil attracts it by forming an S pole at that end.
Q7 · 2 marks · Short answerHarder board level
A conductor is moved parallel to the magnetic field lines between two poles. Is a current induced? Explain.
Hint
Does it cut the field lines?
Answer
No. Moving parallel to the field, the conductor does not cut the field lines, so the field linked with the circuit does not change and no emf is induced.
Q8 · 2 marks · Short answerHarder board level
A magnet is pushed into a coil first slowly and then quickly. Compare the galvanometer deflections and explain.
Hint
Rate of change.
Answer
The deflection is larger when the magnet is pushed quickly, because the magnetic field through the coil changes faster, inducing a larger emf and current.
Q9 · 2 marks · Short answerHOTS / competency
A simple one-coil AC generator turns at 1500 rotations per minute. (a) Find the frequency and time period of its output. (b) At what speed must it turn to give 50 Hz?
Hint
Rotations per second = frequency.
Answer
(a) $\frac{1500}{60} = 25$ rotations per second, so $f = 25$ Hz and $T = \frac{1}{25} = 0.04$ s. (b) 50 rotations per second (3000 per minute).
Q10 · 2 marks · Short answerHOTS / competency
A light aluminium ring rests on top of a vertical coil with a soft iron core. When the switch connecting the coil to a supply is closed, the ring jumps up. Explain.
Hint
Switching on changes the field.
Answer
Closing the switch makes the magnetic field through the ring grow, which induces a current in the ring. By Lenz's law this current opposes the change, so the ring's face becomes a like pole to the coil's top and is repelled upwards.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Energy conversion in an AC generator?Show answer
Mechanical to electrical.
2.Which rings does an AC generator use?Show answer
Slip rings.
3.Frequency of household AC in India?Show answer
50 Hz.
4.Law giving the direction of induced current?Show answer
Lenz's law (opposes the change).
5.Induced current with a magnet at rest in a coil?Show answer
Zero.

Electromagnetic Induction and the AC Generator: frequently asked questions

What is electromagnetic induction?

It is the production of an emf, and a current in a closed circuit, when the magnetic field linked with a conductor changes, for example when a magnet moves relative to a coil.

What does Fleming's right-hand rule give?

The direction of the induced current in a conductor moving across a magnetic field: forefinger along the field, thumb along the motion, middle finger gives the current.

Why is AC preferred to DC for power supply?

AC can be stepped up or down easily with transformers, so it can be transmitted at high voltage over long distances with less energy loss, and AC generators are simpler for large-scale generation.