The greater the current, the greater is the heat produced.
- Connect the terminals of a cell with a wire for a few seconds. The wire will get very hot. The wire has a low resistance, which allows a large current to flow in the circuit. This produces a large amount of heat, which makes the wire hot.
- Connect a bulb to the cell. The resistance of the circuit increases because of the higher resistance of the bulb. Higher resistance means smaller current through the circuit. So, the heat produce in the wire is less. In this wire do not become warmer.