Question

A lens collects light and focuses it into a small spot. this increases the ________ of the light wave. w

Answer 1

The correct answer is intensity.
In fact, intensity I is a measure of the power P of the wave per unit of area A:

`I= (P)/(A)`
The lens does not change the power of the source which emits the wave, however it reduces the area A, since it is focusing the light into a single point. Since A decreases, I, the intensity, increases.