When light from one source, X, strikes a metal, electrons are ejected. When light from another source, Y, strikes the same metal, electrons are not ejected.

Question

Which best explains why this occurs?

Light from source X has a higher intensity than light from source Y.
Light from source X has a lower intensity than light from source Y.
Photons of light from source X carry more energy than photons of light from source Y.
Photons of light from source X carry less energy than photons of light from source Y.

Answer 1

The best explanation for why electrons are ejected when light from source X strikes the metal and not when light from source Y strikes the same metal is:

Photons of light from source X carry more energy than photons of light from source Y.

This relates to the photoelectric effect, where electrons are ejected from a metal surface when they absorb photons with sufficient energy. If the energy of the photons from source X is greater than the work function of the metal, electrons will be ejected. In contrast, if the energy of the photons from source Y is lower than the work function, no electrons will be ejected, regardless of intensity.