## Question

In Young’s experiment the interval between the slits is 0.200 mm. For the light of wavelength 600 mμ, interference fringes are formed on a screen at a distance of 80.0 cm. (i) What is the distance of the second dark fringe from the central fringe? (ii) What is the distance of the second bright fringe from the central fringe?

### Solution

0.360 cm, 0.480 cm

(i) In Young’s double-slit experiment, the distance of the *m* th dark fringe from the central (bright) fringe is given by

Here *d* = 0.200 mm = 0.2000 cm, *D* = 80.0 cm, λ = 600 milimicron^{*} = 600 × 10^{–7}cm. For the second dark fringe *m* = 2. Hence the distance of the second dark fringe from the central fringe is

(ii) The distance of the *m* th bright fringe from the central fringe is given by

For the second-order bright fringe, *m* = 2. Hence the distance of the second bright fringe from the central fringe is

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