Question
An iron nail wrapped with copper wire and connected to a battery acts like a magnet when current flows — but stops attracting pins the moment you disconnect the battery. What is this device? How is it different from a bar magnet?
Solution — Step by Step
An electromagnet is a temporary magnet made by passing electric current through a coil of wire wrapped around an iron core. The iron nail in the question becomes magnetic only when current flows through the coil.
The coil alone produces a weak magnetic field. Iron is a soft magnetic material — it gets magnetised easily when placed inside the coil and boosts the overall magnetic strength significantly. This is why we use iron, not copper or wood.
Since the magnetism depends on current, we control the electromagnet by switching the circuit on or off. No current = no magnetism. This is the defining feature that separates it from a bar magnet.
A bar magnet or horseshoe magnet is made of hard magnetic material (like steel) that retains its magnetism permanently — no battery needed, no on/off control. The Earth’s magnetic field or strong external magnets aligned the domains in the steel, and they stay that way.
| Feature | Electromagnet | Permanent Magnet |
|---|---|---|
| Needs current? | Yes | No |
| Can be switched off? | Yes | No |
| Strength adjustable? | Yes (change current) | No |
| Material | Soft iron core + coil | Steel / hard material |
| Example | Electric bell, MRI machine | Bar magnet, compass |
Why This Works
When current flows through a wire, it creates a magnetic field around it — this is Oersted’s effect, discovered in 1820. Winding the wire into a coil (solenoid) concentrates and adds up all these tiny fields, making the overall field much stronger.
The iron core amplifies this further. Inside the solenoid, the iron’s tiny magnetic regions (domains) align with the field. The moment current stops, the domains in soft iron scramble back to random orientations — so the magnetism vanishes instantly.
Permanent magnets use steel, where domains stay locked in place even after the external field is removed. That’s the entire difference: the ability of the material to retain domain alignment.
Increasing the number of turns in the coil OR increasing the current from the battery makes the electromagnet stronger. This came as a direct question in CBSE Class 7 SA2 pattern — “State two ways to increase the strength of an electromagnet.”
Alternative Method
You can also think of this using a simple analogy. Imagine a crowd of people all pointing in random directions (iron domains before current). When a teacher shouts a command (current flows), they all turn the same way — the room now has a “direction.” Switch off the speaker, and everyone turns random again. That’s soft iron.
Now imagine the crowd is glued in one direction after the command — they can’t turn back even when the speaker is off. That’s steel/permanent magnet.
This mental picture directly maps to why we choose soft iron for electromagnets: easy to magnetise, easy to demagnetise.
Common Mistake
Many students write: “An electromagnet loses its magnetism when the battery runs out.” This is wrong framing. The electromagnet loses magnetism when the circuit is broken (switch off, wire disconnects) — not specifically when the battery runs out. Both cases stop current flow, but the reason matters in a 2-mark answer. Write: “An electromagnet is active only when current flows through the coil.”
Also watch out for this one: students sometimes say copper wire becomes the magnet. The copper wire is just the conductor — the iron core becomes the magnet. If there’s no iron core, you still get a magnetic effect from the coil, but far weaker and with no “core magnet” to speak of.