Induced magnetism is the magnetism that appears in a piece of iron (or steel) when it is placed in the field of a magnet. The end nearest the magnet becomes the opposite pole, so the iron is attracted.
Questions on this appear in magnetism and fields as “explain why the nail is attracted” or “state the pole formed at the end of the nail”.
What happens inside the iron?
Iron is a magnetic material. Inside it are tiny regions that each act like very small magnets, but in an unmagnetised piece they point in random directions and their effects cancel out.
When a magnet’s pole comes near, its field lines up those regions so that more of them point the same way. The piece of iron now has a north end and a south end. It has become a magnet by induction.
Why does the iron end up attracted?
The end of the iron nearest the magnet’s pole becomes the opposite pole. Opposite poles attract, and the attraction is at the near end, which is close to the magnet. The far end becomes the same pole as the real magnet and is pushed away, but it is further away, so the pull wins.
This is why a magnet attracts iron whichever pole you bring up. Only the pole formed in the iron changes, not the outcome.
How to write the explanation
A clear answer has four short links:
- The iron is a magnetic material.
- The field of the magnet induces magnetism in it.
- The end nearest the magnet becomes the opposite pole.
- Unlike poles attract, so the iron is pulled towards the magnet.
Worked example
The north pole of a bar magnet is brought close to the head of an unmagnetised iron nail. The nail is attracted and a second nail hangs from the first. Explain this, and state the pole at each end of each nail. (Invented situation.)
Step 1. The north pole induces magnetism in the first nail. The end nearest the magnet, the head, becomes a south pole. The pointed end becomes a north pole.
Step 2. The pointed north end of the first nail now induces magnetism in the second nail. The end of the second nail nearest it becomes a south pole, and its far end a north pole.
Step 3. Every touching pair of ends is a north and south pair, so there is attraction at each joint. The chain hangs from the magnet.
Step 4. If the magnet is pulled away, the nails lose most of their magnetism and the chain falls apart. Iron is a temporary magnet.
Notice that the whole explanation comes from two ideas: induction makes the near end opposite, and unlike poles attract.
The mistake to watch for
A common slip is to say the nail becomes a magnet with the same pole near the magnet.
Mistaken answer: “The north pole of the magnet makes the end of the nail a north pole, so they attract.”
This breaks a basic rule: two north poles repel, so the nail would be pushed away.
The correction is to write “the near end becomes the opposite pole, so they attract”. If your answer has like poles attracting, check the sentence again.
Another slip is to say the magnet “sticks” to the nail because iron is “sticky”. Name induced magnetism instead.
Check yourself
1. The south pole of a magnet is brought near a steel paper clip. Which pole forms at the end of the clip nearest the magnet?
Show answer
A north pole forms. The induced pole is always the opposite of the magnet pole that is nearby.
2. Why is a plastic ruler not attracted to a magnet?
Show answer
Plastic is not a magnetic material, so no magnetism is induced in it. There is no pole to attract.
3. An iron nail is attracted to both ends of a bar magnet. Does that show the nail is a magnet?
Show answer
No. Attraction is what induction produces in an unmagnetised piece of iron as well. The lesson on magnetic tests explains which result is reliable.
Where this leads next
Next, compare how iron and steel behave once the magnet is removed in permanent and temporary magnetic behaviour, then try the practice set.
Explaining a chain of cause and effect in a few clear sentences is a skill of its own. Our teachers can help you build it in online one-to-one Physics tuition.