Question

The circuit diagram illustrates a copper bar placed on two copper wires stretched over a wooden base placed between two poles of magnets. This entire setup is placed on a compression balance, which shows a weight of 0.4 kgf.

1. What will be the observation of the compression balance when we close the switch?
2. How will this observation change when we increase the current in the circuit?
3. Name the rule used to come to the conclusion in (a).

Answer 1

1. When the switch is closed, current flows through the copper bar. The bar now experiences a magnetic force. In the given diagram, the force is directed downwards, so the bar presses more on the balance. Hence, the reading of the compression balance increases from 0.4 kgf.
2. The magnetic force increases with the current because $$F = B I l$$. So when the current is increased, the reading of the balance increases further.
3. Fleming's left-hand rule.