NCERT Solutions Curiosity Chapter 4 –50Section 4.1.1 Electromagnets — Activity 4.3: Let us experiment
Book page 49 Updated on2026-09-05
Q1.
Connect the two ends of the coil with the terminals of the cell as shown in Fig. 4.3c and observe the magnetic compasses. Do you find any deflection in the needles of the compasses?
Answer
Yes. Both compass needles are deflected as soon as the coil is connected — even though the coil is only wound on a paper cylinder and there is no iron in it at all.
Why it happens: the coil is now carrying a current, so it produces a magnetic field. Each of the 50 turns contributes its own field and, because every turn is wound in the same direction, the fields add up along the axis of the cylinder. The result is a field strong enough to turn the needles at both ends. The paper cylinder plays no part in this — it is only a former to hold the shape of the coil.
Check it yourself: the two needles turn in opposite senses, because they are facing the two different ends of the coil. That is your first clue that the coil, like a bar magnet, has two ends of opposite kind.
Q2.
Disconnect the wire from the cell. Do the needles of the compasses come back to their original positions?
Answer
Yes. Both needles swing back and rest once more along the north–south direction.
Why it happens: with the cell disconnected there is no current, so the coil produces no magnetic field. The only magnet acting on the needles is the Earth, and a freely turning needle in the Earth's field settles north–south. The coil is magnetic only while the current flows.
Q3.
Insert an iron nail in the paper cylinder (Fig. 4.3d) and repeat the steps. Is there any difference in the deflection of the compass needles?
Answer
Yes — the deflection is much larger with the iron nail inside than with the empty paper cylinder, for exactly the same cell and the same coil.
Core inside the coil
Deflection of the compass needles
Can it hold clips?
Nothing (air, paper cylinder only)
Small
No, or barely
Iron nail
Much larger
Yes
Why the iron makes such a difference: iron is a magnetic material. Placed inside the coil's magnetic field, the nail becomes a magnet itself, and its magnetism is added to the field the coil was already making. The total field is therefore far stronger than the coil alone can produce — which is why, for practical use, most electromagnets are given an iron core.
Why an electromagnet is strong: many turns adding up, plus an iron core that becomes a magnet itself.
Q4.
Place some iron paper clips near the two ends of the nail. Are the clips attracted to the ends of the nail?
Answer
Yes. The clips are pulled towards the two ends of the nail and hang there while the current flows (Fig. 4.3e). Stop the current and they drop.
Why they gather at the ends: the coil with its iron core is now behaving as a magnet, and in any magnet the magnetic effect is strongest at the two poles. The middle of the nail, wrapped in the coil, attracts far less. So the clips collect where the pull is greatest — at the ends.
Try This: count how many clips hang at each end. Then add a second cell and count again. You have just measured, roughly, how the strength of an electromagnet depends on the current.