The curve drawn between the velocity and frequency of a photon in a vacuum will be a

$(a)$ 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. Explain why?
$(b)$ When light travels from a rarer to a denser medium,the speed decreases. Does the reduction in speed imply a reduction in the energy carried by the light wave?
$(c)$ In the wave picture of light,intensity of light is determined by the square of the amplitude of the wave. What determines the intensity of light in the photon picture of light?

What is a photon?

The momentum of a photon is $2 \times 10^{-16} \text{ g} \cdot \text{cm/s}$. Its energy is:

$10^{20}$ photons of wavelength $660 \ nm$ are emitted per second from a lamp. The wattage of the lamp is (Planck's constant $h = 6.6 \times 10^{-34} \ J \cdot s$). (in $W$)

$A$ proton moving with a momentum $p_{1}$ has a kinetic energy $1/8$th of its rest mass-energy. Another light photon having energy equal to the kinetic energy of the proton possesses a momentum $p_{2}$. Then,the ratio $\frac{p_{1}-p_{2}}{p_{1}}$ is equal to