In a Young’s double–slit arrangement

PHYSICS · Multi-part · A Level · Physics · Waves · Waves

Problem

In a Young’s double–slit arrangement, two very narrow slits separated by a distance

d

are illuminated by monochromatic light of wavelength

\lambda

. The screen is kept at a distance

D

(

D \gg d

). (a) Derive an expression for the separation between successive bright fringes on the screen in terms of

D,\;\lambda

and

d

. Clearly state the assumptions used. (b) Taking

\lambda = 600\,\text{nm}

d = 0.25\,\text{mm}

and

D = 1.2\,\text{m}

, calculate the fringe width produced. (c) If the slit separation is decreased by

10\%

while

\lambda

and

D

remain unchanged, determine the percentage change in the fringe width obtained in part (b).