1) Consider an oil film (n = 1.50) on water (n = 1.33) and 600nm incident light.

Question

1) Consider an oil film (n = 1.50) on water (n = 1.33) and 600nm incident light. The minimum film thickness for constructive inteference is:

2) A diffraction grading has 6000 lines per centimeter ruler on it. What is the angular separation between the second and third orders on the same side of the central order when the grating is illuminated with a beam of light of wavelength 550 nm?

3) A polarizer (with its preferred direction rotated 30 degrees to the vertical) is placed in a beam of unpolarizied light of intensity 1. After passing through the polarizer, the beam's intensity is:

Explanation / Answer

1) 100 nm

2)

sin(?n)/N = n?

n --> order of maxima

?n --> Angle corresponding to nth order maxima

N --> number of lines per meter = 6 x 105

sin(?2) = 2 x 550 x 10-9 x 6 x 105 = 0.66

=> ?2 = 41.3

sin(?3) = 3 x 550 x 10-9 x 6 x 105  = 0.99

=> ?3 = 81.9

Therefore, the angular separation between the second and third orders

= ?3 - ?2 = 40.6

3)

Intensity of the unpolarised light I = 1

Intensity of the polarised light after passing throughpolariser I ' = I / 2

Since it does not depend on orientation of the polariser

So, I ' = 1/ 2 = 0.5

Note : If two polarisers are there then orientation playsimportant role according to Malus law

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