SATHEE: Optics Question 1147

Optics Question 1147

Question: A light of wavelength $5890 A A$ falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light

[Pb. PMT 2003]

Options:

A) $2.945 \times 10^{- 7} m$

B) $3.945 \times 10^{- 7} m$

C) $4.95 \times 10^{- 7} m$

D) $1.945 \times 10^{- 7} m$

Show Answer

Answer:

Correct Answer: A

Solution:

If thin film appears dark 2mt cos r = nl for normal incidence $r = 0^{o}$

Therefore 2 m t = nl

Therefore $t = \frac{n λ}{2 μ}$

Therefore $t_{min} = \frac{λ}{2 μ}$ = $\frac{5890 \times 10^{- 10}}{2 \times 1}$

$= 2.945 \times 10^{- 7} m$ .

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Optics Question 1147

Question: A light of wavelength 5890AA falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light

Options:

Answer:

Solution:

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Question: A light of wavelength $5890 A A$ falls normally on a thin air film. The minimum thickness of the film such that the film appears dark in reflected light