# Amplitude of light and intensity

## Homework Statement

Light is emitted from a point source. How does amplitude of light change when light has travelled from R to 2R?

## Homework Equations

Energy=(1/2)kA^2 where k is constant and A is amplitude
Intensity=(Energy/time)/area

## The Attempt at a Solution

My teacher said that:
As area=4piR^2, intensity of light decreases when light travels to 2R. Therefore the amplitude of light decreases. Isn't the energy be constant while intensity changes? I am confused as he said that amplitude of light decreases as light moves further from the source?

What is the cause of the phenonmenon that light becomes dimmer in further distance? Decrease of intensity or decrease of amplitude or both?