Explain the following giving reasons :
`(i)` When monochromatic light is incident on a surface separating two media, the reflected and refracted light both have the same frequency as the incident frequency.
`(ii)` When ligjt travels from a rarer to a denser medium, the speed decreases. Does this decrease in speed imply a reduction in the energy carried by the wave ?
`(iii)` In the wave picture of light, intensity of light is determined by the square of the amplitude of the wave. What determines the intensity in the photon picture of light ?

Explanation

`(i)` Frequency is intrinsic property of a wave, which does not change when it goes from one medium to other. Only wavelengths and speed of the wave changes.
`(ii)` No. Because energy is `E=hv` and `v` remains same.
`(iii)` Number of photons striking per unit area per unit time.