ScienceCBSE Class 8 · Electricity: Magnetic and Heating Effects

Magnetic Effect of Electric Current and Electromagnets: Class 8 Science

Updated 17 October 2026 · Fact-checked

When electric current flows through a conductor it produces a magnetic field around it, and the field disappears when the current stops. This is the magnetic effect of electric current, found by Oersted in 1820. A current-carrying coil, especially with an iron core, behaves as an electromagnet whose strength depends on the current and the number of turns, and whose poles reverse when the current is reversed.

Understand Magnetic Effect of Electric Current and Electromagnets

Compass and a wire (Activity 4.1). A magnetic compass needle is a tiny magnet. When the switch is closed so that current flows through a wire stretched above the compass, the needle deflects; when the switch is opened it returns to its original direction. So a current-carrying wire has a magnetic effect. The region around a magnet or a current-carrying wire where its magnetic effect can be felt, for example by the deflection of a compass needle, has a magnetic field. The magnetic effect acts through non-magnetic materials kept in between.

Oersted. Hans Christian Oersted (1777 to 1851), a professor in Denmark, noticed in 1820 that the needle of a compass near an electric circuit deflected when the circuit was closed or opened. After making sure the current produced the field he published his finding, and other scientists repeated the experiment. This showed that electricity and magnetism are linked.

Electromagnet (Activities 4.2 to 4.4). A wire wound into a coil and connected to a cell behaves like a magnet: it deflects a compass needle at both ends. When an iron nail is placed in the core, the coil becomes a stronger magnet and picks up iron paper clips; when the current is stopped, the clips fall. A current-carrying coil that behaves as a magnet is an electromagnet. An electromagnet has two poles, north and south. If the north pole of the compass is attracted to end A, then A is a south pole. Join a cell for only a few seconds, as the cell weakens quickly.

What changes the strength and poles? A single cell gives a small current and a weak field. More cells in a battery give a larger current and a stronger field, so the compass deflects more and more clips are lifted. More turns of the coil also give a stronger magnet. The strength can therefore be changed by changing the current, the number of turns, or both. Reversing the direction of the current reverses the poles.

Uses. Lifting electromagnets hung from cranes in factories and scrap yards are switched ON to lift iron and steel objects and OFF to release them. The magnetic effect is also used in electric bells, motors, fans and loudspeakers.

Earth as a magnet. The movement of liquid iron deep inside the Earth creates electric currents which produce the Earth's magnetic field; many migratory animals use it to navigate and it shields us from harmful particles from space. The book hints that just as electricity gives magnetism, a moving magnet can produce an electric current, which you will meet in higher classes.

Magnetic Effect of Electric Current and Electromagnets: formulas and key facts

Magnetic effect of current: Current in a conductor > magnetic field around it | Current stops > field disappears; Detected by the deflection of a compass needle.
Electromagnet: Insulated wire coil + current (+ iron core) > magnet with two poles; An iron core makes it stronger.
Strength of an electromagnet increases with: More current (more cells)
More turns of the coil
Iron core; Changes in the first two are listed in the chapter.
Reversing poles: Reverse direction of current > poles interchange; Repeat Activity 4.4 with the cell reversed.
Polarity by compass: North pole of compass attracted to an end > that end is a south pole; Unlike poles attract.

How to solve Magnetic Effect of Electric Current and Electromagnets questions

Use this method for questions on the magnetic effect of current.

1Check whether current is flowing: closed circuit and a working cell.
2If a compass needle is near and current flows, expect a deflection; if the switch is OFF, expect the original direction.
3For an electromagnet, ask what changes: number of cells, number of turns, iron core, direction of current.
4Increase in current or turns gives a stronger magnet; compare in clips lifted or compass deflection.
5To find a pole, use unlike poles attract with the compass.
6Add a safety note: do not leave the cell connected for long.

Magnetic Effect of Electric Current and Electromagnets 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.

Counting clips lifted

Suppose in a school lab an electromagnet with 50 turns and a single 1.5 V cell lifts 4 paper clips. Imagine that with two cells in the same coil it lifts 9 clips, and with two cells and 100 turns it lifts 17 clips. These are invented readings.

(a) Which change gave the larger gain in clips: adding a cell, or doubling turns (with two cells)? (b) By what percentage did the number of clips increase when going from 1 cell to 2 cells? (c) What do these readings show about the strength? (d) Suggest why the cell must not stay connected for long.

Try it first, then show the solutionSolution

Adding a cell: 9 − 4 = 5 more clips. Doubling the turns: 17 − 9 = 8 more clips. So doubling the turns gave the larger gain here.
Percentage increase = 5 ÷ 4 × 100 = 125%.
More current or more turns gives a stronger electromagnet that lifts more clips.
The cell weakens quickly if connected for more than a few seconds.

Answer: (a) Doubling the turns (8 clips against 5); (b) 125%; (c) strength rises with current and turns; (d) the cell weakens quickly.

Memory hook: More push, more loops, stronger magnet.

Scrap-yard crane

Imagine a crane with a lifting electromagnet picks up iron scrap, then the operator switches it OFF over a truck.

(a) Why does the scrap fall when the current is switched off? (b) Could the same crane lift a copper block? (c) What does an iron core do?

Try it first, then show the solutionSolution

When the current stops, the magnetic field disappears, so the scrap is released.
A magnet attracts iron and steel; the chapter describes lifting iron and steel objects, so copper, which is not magnetic, would not be lifted (an inference from magnetic materials in Class 6).
The iron core makes the electromagnet stronger.

Answer: (a) The magnetic field disappears; (b) no, it is not magnetic; (c) it strengthens the magnet.

Memory hook: Switch ON to grab, switch OFF to drop.

Tricks to remember Magnetic Effect of Electric Current and Electromagnets

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

No current, no magnet
An electromagnet is a magnet only while the switch is ON.
Use it when: Temporary magnet questions.
Cells, Coils, Core
Three Cs make an electromagnet stronger: more Cells, more Coil turns, an iron Core.
Use it when: Factors affecting strength.
Unlike attracts
If the compass N points toward the end, that end is S.
Use it when: Finding polarity.

Magnetic Effect of Electric Current and Electromagnets: solved examples

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

Example 1: Observation in Oersted's experiment · 3 marks · Short answerBoard level

Describe what is observed in a compass placed below a wire when (a) the switch is ON and (b) the switch is OFF. What does it show?

Try it first, then show the solutionSolution

(a) The needle deflects from its original direction. (1)
(b) The needle returns to its original position. (1)
It shows that a current-carrying wire produces a magnetic field, which disappears when the current stops. (1)

Answer: Needle deflects with current and returns when off, so a current produces a magnetic field.

Example 2: What is an electromagnet · 1 mark · MCQBoard level

A current-carrying coil that behaves as a magnet is called
(a) a bar magnet
(b) an electromagnet
(c) a compass
(d) a conductor

Try it first, then show the solutionSolution

The coil with current is an electromagnet.

Answer: (b)

Example 3: Making and strengthening an electromagnet · 5 marks · Long answerHarder board level

(a) Describe how you would make an electromagnet using an iron nail, insulated wire and a cell. (2) (b) State three ways to make it stronger. (3)

Try it first, then show the solutionSolution

(a) Wind about 50 turns of insulated wire tightly around the nail; join the ends to the cell for a few seconds only; the nail picks up iron clips. (2)
(b) Use more cells (larger current); increase the number of turns; make sure an iron core is present. (3)

Answer: Coil insulated wire on an iron nail and connect to a cell briefly; strengthen with more cells, more turns, an iron core.

Example 4: Finding poles with a compass · 4 marks · Case-basedHarder board level

Read the passage and answer.

An electromagnet has ends A and B. When connected to a cell, the north pole of a compass held near A is attracted toward A. When the cell is reversed, the north pole is pushed away from A.
(a) Name the pole at A in the first case. (1)
(b) Name the pole at B in the first case. (1)
(c) What happens to the poles after the cell is reversed? (1)
(d) Why does an electromagnet not hold clips when disconnected? (1)

Try it first, then show the solutionSolution

(a) South pole, because unlike poles attract. (1)
(b) North pole, since the two ends have opposite polarity. (1)
(c) They interchange: A becomes north and B south, so the compass north is pushed away from A. (1)
(d) With no current there is no magnetic field. (1)

Answer: (a) South; (b) North; (c) poles interchange; (d) no current, no field.

Example 5: Forgotten switch · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

Sumana forgets to switch OFF her model lifting electromagnet. After a while the nail no longer picks up paper clips, but the wire around the nail is still warm.
(a) Suggest a reason why it stopped lifting. (1)
(b) Why is the wire warm? (1)
(c) Suggest one test with a fresh cell to check your reason. (1)
(d) How would she make the model lift more clips? (1)

Try it first, then show the solutionSolution

(a) The cell has weakened (run down) because the chemicals are used up, so the current is too small to magnetise the nail well. (1)
(b) The current heats the wire (heating effect). (1)
(c) Replace the cell with a fresh one; if the nail now lifts clips the old cell was the reason. (1)
(d) More cells or more turns of wire. (1)

Answer: (a) Weak cell; (b) heating effect; (c) try a fresh cell; (d) more turns or cells.

Where students lose marks in Magnetic Effect of Electric Current and Electromagnets

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

Mistake: Saying the electromagnet keeps its magnetism after the current stops.
Confusing it with a permanent magnet.
Wrong working
The nail remains a magnet after the cell is removed.
Right working
The coil loses its magnetic effect when the current stops.
Do this: Use 'temporary magnet'.
Usually costs: 1 mark.
Mistake: Writing that the compass deflects because of the heat.
The wire becomes warm too.
Wrong working
The needle moves because the wire is hot.
Right working
The needle moves because of the magnetic field produced by the current.
Do this: Link deflection with magnetic field.
Usually costs: 1 mark.
Mistake: Not naming insulated wire.
Details get skipped.
Wrong working
Wrap a wire around a nail.
Right working
Wrap insulated wire tightly around the nail and connect to a cell for a few seconds.
Do this: Say 'insulated' and 'for a few seconds'.
Usually costs: ½ mark.
Mistake: Naming the wrong pole from the compass.
Forgetting that unlike poles attract.
Wrong working
North pole of the compass attracted, so that end is north.
Right working
The compass north is attracted, so that end is south.
Do this: Say 'unlike poles attract' in the answer.
Usually costs: 1 mark.

Exam tips

Write both observations, current ON and current OFF, in compass questions.
Give three ways to strengthen an electromagnet: current, turns, iron core.
State that the electromagnet is temporary.
Mention the safety point of not leaving the cell connected for long.
Use dates exactly: Oersted, 1820.

Practice questions on Magnetic Effect of Electric Current and Electromagnets

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

Q1 · 2 marks · Very short answerBoard level
State two ways of reversing the poles or changing the strength of an electromagnet.
Hint
One is about direction, one about size.
Answer
Reverse the direction of the current to interchange the poles (1); change the number of cells or turns to change the strength (1).
Q2 · 1 mark · MCQBoard level
Who found that an electric current produces a magnetic field?
(a) Galvani
(b) Volta
(c) Oersted
(d) Hooke
Hint
The year was 1820.
Answer
(c)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): An electromagnet with an iron core lifts more clips than the same coil without a core.
Reason (R): The iron core makes the electromagnet stronger.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Activity 4.3 compares coil with and without a nail.
Answer
(a) R explains A.
Q4 · 4 marks · Short answerHarder board level
In a trial an electromagnet lifted 6 clips with one cell and 15 clips with three cells, same coil. (a) By how many times did the number of clips grow? (b) By what percentage? (c) With three cells and double the turns it lifted 30 clips; how many more than with three cells? (d) What conclusion do you draw?
Hint
15 ÷ 6 = 2.5.
Answer
(a) 15 ÷ 6 = 2.5 times. (b) (15 − 6) ÷ 6 × 100 = 150%. (c) 30 − 15 = 15 more. (d) More current and more turns make the electromagnet stronger (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
A student shows a coil connected to a cell, with no iron inside, attracting a compass needle. She says: 'It is not a magnet because it has no iron.' The cell is then taken off.
(a) Is she right? (b) What happens to the compass when the cell is removed? (c) How could she make the coil stronger? (d) Why can the same coil not be called a permanent magnet?
Hint
Activity 4.3 without and with the nail.
Answer
(a) No: the coil acts as an electromagnet even without iron; iron only makes it stronger. (b) It returns to its original direction. (c) Insert an iron nail, add cells or turns. (d) It is a magnet only while the current flows (1 mark each).

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.What did Oersted notice in 1820?Show answer
A nearby compass needle deflected when an electric circuit was closed or opened.
2.What is a magnetic field?Show answer
The region around a magnet or current-carrying wire where its magnetic effect is felt.
3.How do you reverse the poles of an electromagnet?Show answer
Reverse the direction of the current.
4.Name two devices that use the magnetic effect of current.Show answer
Electric bell and electric motor (also fans, loudspeakers).
5.What is the use of a lifting electromagnet?Show answer
To lift and sort heavy iron and steel objects in factories and scrap yards.

Magnetic Effect of Electric Current and Electromagnets: frequently asked questions

Does the wire need to be insulated for an electromagnet?

Yes. The activities use insulated wire so that the turns do not touch and the current flows through the coil.

Why does an iron core make the electromagnet stronger?

The chapter reports that with an iron nail in the core the coil becomes a stronger magnet and the compass deflection is much more; most practical electromagnets therefore have an iron core.

Why does Earth behave like a magnet?

According to the chapter, movement of liquid iron in the core creates electric currents which generate the Earth's magnetic field.

Can a magnet produce current?

The book says you will learn in higher classes that a moving magnet can lead to an electric current.