You are here
Electromagnets
- Wrap a wire into a coil and pass current through it.
- The coil then behaves like a magnet.
- It can deflect a compass needle and pick up iron clips.
- When the current stops, the coil loses its magnetism.
- An iron core inside the coil makes it stronger.
Example 1 — Coil Without Nail
- Current flows through a plain coil.
- It deflects the compass a little.
- So the coil acts as a weak magnet.
Example 2 — Coil With Iron Nail
- An iron nail is put inside the coil.
- The deflection is much more and it lifts clips.
- So the iron core makes the magnet stronger.
Important Points
- Like a bar magnet, an electromagnet has two poles — North and South.
- Its strength grows with more current or more coil turns.
- Its poles reverse if the direction of current is reversed.
Definition — Electromagnet
An electromagnet is a current carrying coil that behaves as a magnet. Most have an iron core to make them stronger.
Materials needed
About 50 cm of flexible insulated wire.
An iron nail and an electric cell.
A few iron paper clips.
An iron nail and an electric cell.
A few iron paper clips.
Procedure
Wrap the wire tightly around the nail as a coil.
Connect the wire ends to the cell for only a few seconds.
Bring the nail near the clips and lift.
Then disconnect the wire and watch the clips.
Connect the wire ends to the cell for only a few seconds.
Bring the nail near the clips and lift.
Then disconnect the wire and watch the clips.
Observation
When current flows, the clips cling to the nail. When current stops, the clips fall off.
Explanation
The coil with the nail acts as a magnet only while current flows. So this is an electromagnet.
◆ Summary
- Coil round a nail.
- Current ON, clips cling.
- Current OFF, clips fall.
- This is an electromagnet.
Materials needed
About 100 cm of flexible insulated wire.
A chart paper tube and an iron nail.
An electric cell and two magnetic compasses.
A few iron or steel paper clips.
A chart paper tube and an iron nail.
An electric cell and two magnetic compasses.
A few iron or steel paper clips.
Procedure
Wind about 50 turns of wire on the tube to make a coil.
Place a compass near each end of the coil.
Connect the coil to the cell and watch the needles.
Insert an iron nail in the tube and repeat.
Place clips near the ends of the nail.
Place a compass near each end of the coil.
Connect the coil to the cell and watch the needles.
Insert an iron nail in the tube and repeat.
Place clips near the ends of the nail.
Observation
The coil deflects the compass needles. With the iron nail inside, the deflection is much more and it attracts clips. When current stops, the coil loses its magnetism.
Explanation
The coil acts like a magnet only with current. An iron core makes it a much stronger magnet.
◆ Summary
- Coil deflects compasses.
- Iron core, more deflection.
- It attracts iron clips.
- Current OFF, effect gone.
Materials needed
The electromagnet made in Activity 4.3.
A magnetic compass.
A magnetic compass.
Procedure
Label the two ends of the coil as A and B.
Place the compass near end A.
Connect the coil to the cell and watch the compass.
Note which pole is attracted to end A.
Repeat for end B.
Place the compass near end A.
Connect the coil to the cell and watch the compass.
Note which pole is attracted to end A.
Repeat for end B.
Observation
If the north pole of the compass is pulled to end A, then end A is a south pole. End B is the opposite pole.
Explanation
Unlike poles attract. So the compass tells us the pole of each end. An electromagnet has two poles, like a bar magnet.
◆ Summary
- Unlike poles attract.
- End A is one pole.
- End B is opposite.
- Two poles, like a magnet.
🔭 Think Like a Scientist — Changing the Strength
Repeat Activity 4.3 with 2 and 4 cells, and with different numbers of coil turns. What do you observe?
What you find
One cell gives a small current, so the magnet is weak and the deflection is less. More cells give a larger current, so the magnet is stronger and lifts more clips. More turns of the coil also make it stronger. Reversing the current direction reverses the poles.
⭐ A Step Further — Why Earth Is a Magnet
A freely hung magnet rests in the north–south direction because Earth itself acts like a giant magnet.
Deep inside Earth, moving liquid iron makes electric currents, which make a magnetic field. Many birds, fish, and animals use this field to find their way. The field also shields life from harmful particles from space.
