Question

In a meter bridge experiment, the key (K) in the main circuit is kept open when readings are not being taken. What is the main reason for this?

Options

• The EMF of the cell will decrease

• The value of resistance will change due to Joule heating effect

• The galvanometer will stop working

• None of these

Answer 1

The value of resistance will change due to Joule heating effect

Explanation:

When current flows continuously through the resistance wire, it generates heat (Joule heating), which causes the temperature of the wire to rise. This changes its resistance and introduces error in the measurement. Therefore, the key is kept open when readings are not being taken to prevent this heating effect.