1. The problem statement, all variables and given/known data Light is emitted from a point source. How does amplitude of light change when light has travelled from R to 2R? 2. Relevant equations Energy=(1/2)kA^2 where k is constant and A is amplitude Intensity=(Energy/time)/area 3. 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? Thanks for answering my question.