Answer:
maybe its heat sorry if it's wrong
because if friction is not in the problem so we are making heat or thermal energy
Answer:
The contribution of the wavelets lying on the back of the wave front is zero because of something known as the Obliquity Factor. It is assumed that the amplitude of the secondary wavelets is not independent of the direction of propagation, Sources: byju's.com
its the 3rd option!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
E = hf
E : photon energy
h : Plank's constant 6.63×10^-34
f : frequency
Hope it helped!