First slide

Coherent sources and their importance in interference

Question

In the Ideal double slit experiment, when a glass – plate (refractive index 1.5) of thickness t is introduced in the path of one of the interfering beams (wavelength $λ$ ) the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass – plate is

Moderate

A

$2 λ$
B

$\frac{2 λ}{3}$
C

$\frac{λ}{3}$
D

$λ$

Solution

$P a t h d i f f e r e n c e d u e t o s l a b s h o u l d b e i n t e g r a l m u l t i p l e o f λ o r Δ x = n λ o r (μ - 1) t = n λ, n = 1, 2, 3............. o r t = \frac{n λ}{μ - 1} F o r m i n i m u m v a l u e o f t, n = 1 ∴ t = \frac{λ}{μ - 1} = \frac{λ}{1.5 - 1} = 2 λ$

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