# A long narrow slit is illuminated by blue light and the diffraction pattern is obtained on a white screen.

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A long narrow slit is illuminated by blue light and the diffraction pattern is obtained on a white screen.

1. How the width of bands change as the distance from the centre increases?

2. What happens to the width of pattern, if yellow light is used instead of blue light?

3. In a double slit experiment, the slits are separated by 0.03 cm and the screen is placed 1.5 m away. The distance between the central fringe and the fourth bright fringe is 1 cm. Determine the wavelength of light used in the experiment.

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1. Width of bands decreases from the centre of the bands

2. The pattern expands or bandwidth increases

3. Xn = $\frac{nλD}{d}$

d = 0.03 cm = 0.03 × 10-2 m

D = 1.5 m, n = 4, xn = 1 cm = 1 × 10-2 m

λ = $\frac{X_nd}{nD}$ = $\frac{10^{-2}\times0.03\times10^{-2}}{4\times1.5}$ = 500 nm