Answer
(a) increase
(b) stay the same
Work Step by Step
(a) We know that originally, light 3 is dark, but when the switch is closed, then light 3 is illuminated and hence its intensity increases.
(b) We know that the intensity of lights 1 and 2 stay the same when the switch is closed. As they have the same potential difference and the same resistance, therefore, from equation $P=\frac{V^2}{R}$, it is clear that they will continue to dissipate the same amount of power.
