Light is observed reflecting from a thin film of oil (index = 1.25) that floats

Question

Light is observed reflecting from a thin film of oil (index = 1.25) that floats on water (index = 1.33). What is the smallest nonzero thickness of the oil that produces constructive Interference in reflection of 600 nm light? 120 nm 150 nm 240 nm 226 nm 300 nm A single slit of size 0.15 mm is Illuminated by light of wavelength 633 nm. What Is the width of the central bright fringe seen on a screen 2 meters from the slit? 4. 7 x105 mm 8.4 mm 34 mm 17 mm 9.5x105 mm A grating having 5000 lines/cm is used with light of wavelength 633 nm. How many total maxima (count central maxima plus all those on either side of the central maxima) a reproduced?

Explanation / Answer

Number 6)

The formula that governs this situation is

2nt = (m + .5)(wavelength)

2(1.25)(t) = (.5)(600 X 10-9)

t = 1.2 X 10-7 m which is 120 nm (Choice A)

Number 7)

Apply y/L = m(wavelength)/a

y/2 = (1)(633 X 10-9)/(1.5 X 10-4)

y = .00844m

Width of Central Max = 2y = 2(.00844)

Width = .017 m which is 17 mm (Choice D)

Number 8)

Apply 1 = m(wavelength)/d

1 = (m)(633 X 10-9)(500000)

m = 3.16

Use the whole number 3 for each side

3+ 3 = 6

Add the central max and 6+1 = 7

The answer is 7, not sure which choice that is since that is cut off in your picture.

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