Red light of wavelength 630 nm passes through two slits and then onto a screen that is 1.4 m from the slits. the center of the 3rd order bright band on the screen is separated from the central maximum by 0.76 cm . a)determine the frequency of the light.
b)determine the slit separation.
c)determine the angle of the third-order bright band.

Part a)

Part b)

Part c)

Explanation:

Part a)

As we know that the speed of light is given as

now the frequency of the light is given as

so we have

Part b)

Position of Nth maximum intensity on the screen is given as

so here we know for 3rd order maximum intensity

n = 3

L = 1.4 m

Part c)

angle of third order maximum is given as

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.