Question

Four identical iron bars are kept on a table. Two out of the four bars are magnets. Out of these, one of the magnets is marked with the north-south poles. How will you find out which of the other three bars is a magnet?

Answer 1

The magnet with known poles will attract and repel two ends of the unmarked magnet. This way, we will be able to identify the magnet bar and iron bar.

The steps to be followed are:

1. Take the bar magnet with known poles in your hand.
2. Take one of the other two iron bars in another hand.
3. Bring one side of the iron bar towards the South pole of the bar magnet and note down whether it is
   attracted or repelled.
4. Bring another side of the iron bar towards the South pole of the bar magnet and again note down the same
   thing.
5. If there is an attraction in both cases (iii) and (iv), then it is definitely a simple iron bar.
6. If there is an attraction in one case and repulsion in another case, then it is a bar magnet.
7. Do the same for the third iron bar.

To find out the poles:

1. The bar is attracted, then it is the North pole of the unmarked bar magnet.
2. If the bar is repelled, then it is obviously a South pole of the identified bar magnet.