Question

A glass plate 2.50 mm thick, with an index of refraction of 1.40, is placed between a source of light with wavelength 540 nm (in vacuum) and a screen. The source is 1.80 cm from the screen.

How many wavelengths are there between the source and the screen?

(HINT: the wavelength of light inside the glass is different!)

Answer 1

`N=0.194`

Step-by-step explanation:

Given:

• refractive index of the glass plate,
  `n=1.4`

• thickness of the glass plate,
  `x=2.5\ mm`

• wavelength of the source light,
  `\lambda=18\ mm`

We know that the refractive index of a medium is given as:

`\rm n=(wavelength\ of\ light\ in\ the\ air\ or\ vacuum)/(wavelength\ of\ light\ in\ the\ medium)`

`n=(\lambda)/(\lambda')`

`1.4=(18)/(\lambda')`

`\lambda'\approx12.857\ mm`

Hence the no. of wavelengths in the glass:

`N=(x)/(\lambda')`

`N=(2.5)/(12.857)`

`N=0.194`