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NEET Easy

In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength  of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same  and D) the separation between the slits needs to be changed to

A

2.1mm

B

1.9mm

C

1.8mm

D

1.7mm

Step-by-Step Solution

Sol. Angular width=λd\text{Angular width} = \frac{\lambda}{d}

0.20∘=λ2 mm…(i)0.20^\circ = \frac{\lambda}{2 \text{ mm}} \quad \dots(i)

0.21∘=λd…(ii)0.21^\circ = \frac{\lambda}{d} \quad \dots(ii)

Dividing we get, 0.200.21=d2 mm\frac{0.20}{0.21} = \frac{d}{2 \text{ mm}}

∴d=1.9 mm\therefore d = 1.9 \text{ mm}

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