Does intensity of light change during refraction? As frequency of light do not changes during refraction does intensity of light also change during refraction
 A: No, the intensity is not same since some part of the  light ray  gets reflected back to the initial medium but maximum part of it is refracted.
A: Intensity of light is related to the energy of the EM wave (power per unit area). So when light passes through an interface some of it is reflected and some refracted. Thus some energy is reflected and some transmitted. Additionally there could be absorption in the medium which further reduces the energy. This all means that the intensity is reduced. 
A: The question is a good one, and has not been addressed by the answers offered so far.
With a good antireflection coating, essentially no light is reflected when a light beam enters a refractive medium.   So, we can say all the light in an incident beam enters the medium. Before the beam enters the medium, we could say that the beam contains a certain amount of energy per unit length (think number of photons per second, times energy per photon, divided by the speed of light). 
Inside the medium, the speed of the beam is dramatically reduced, by, say, 2/3.  So, there we divide by 2c/3 instead of c.  *So the beam's energy per unit length must be greater inside the medium*.
Where does the energy reside?  It's a bit arguable, but one reasonable way to look at it is that the photons have slowed down, and , like a steady stream of cars in a freeway slowdown, they pack together closer while they're going slower.  It would be difficult, though, to count the number of photons per unit length directly. After all, they're not at all like cars or grains of sand.  You would need to infer it, and therein lie the arguments.
A: The answer to your question is not simple, but if you assume monochromatic light, then the intensity of light can be described as:
$$I=\frac{hn\nu}{At}$$
Where n is the number of photons.

For monochromatic radiation, the total energy emitted equals the number of photons n times the energy of one photon, hν.

Are number of photons in an incident radiation proportional to its intensity?
Now when photons travel through a medium, they interact with the atoms/molecules of the medium, and three things can happen:


*

*elastic scattering

*inelastic scattering

*absorption, the photon ceases to exist, and will be re-emitted or not, in case it is not re-emitted, it will heat up the medium/material
Obviously, 1., and 2. does not decrease the number of photons, only 3., and only in case the photon is not re-emitted.
Thus, as the photons travel through the medium, some of them will be absorbed, without being re-emitted, and thus the number of photons could decrease during refraction. Thereby the intensity could decrease too.
A: None of the answers address your questions so far. You are specifically asking about the refracted light and not the reflective light. Original intensity minus reflected intensity equals refracted intensity. The intensity and frequency of the light refracted stays the same.
