Question

Why does an electron emit energy only in the form of light

Answer 1

When an electron is hit by a photon of light, it absorbs the quanta of energy the photon was carrying and moves to a higher energy state.

One way of thinking about this higher energy state is to imagine that the electron is now moving faster, (it has just been "hit" by a rapidly moving photon). But if the velocity of the electron is now greater, it's wavelength must also have changed, so it can no long stay in the original orbital where the original wavelength was perfect for that orbital-shape.

So the electron moves to a different orbital where once again its own wavelength is in phase with its self.