According to the principle of superposition, when two waves meet, they reflect when two waves meet, they interfere when a wave meets a boundary, the angle of the reflected wave is equal to the angle of the incident wave when a wave meets a boundary, the angle of the refracted wave will be equal to the angle of the incident wave

The principle of superposition simply says that when two waves

cross the same place, the effect at that place is the sum of the

effects of each individual wave.

We know that when two waves meet, the amplitude of what happens

at their meeting place can be anything from zero to bigger than either

wave alone. THAT's superposition in action.

When two waves meet, they interfere.

photocells convert light energy to electricity

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.