What is interference of light? Write two essential conditions for… - Vidyadip

Question

What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen. Draw a graph showing the variation of intensity versus the position on the screen in Young's experiment when (a) both the slits are opened and (b) one of the slit is closed. What is the effect on the interference pattern in Young's double-slit experiment when: 32. 33.
i. Screen is moved closer to the plane of slits?
ii. Separation between two slits is increased. Explain.

✓

Answer

Interference of light: Phenomenon of redistribution of light energy in a medium on account of superposition of light waves from two coherent sources is called interference of light.
Conditions for sustained interference: The two essential conditions of sustained interference are as follows:
i. The two sources of light should emit light continuously.
ii. The light waves should be of same wavelength (Monochromatic).
(a) When both the slits are open, we get an interference pattern on the screen. Then the following intensity distribution curve is obtained.

(b) When one of the slits is closed, diffraction pattern is obtained on the screen. The following intensity curve is obtained.

Also we know that, Fringe width, $\beta=\frac{D \lambda}{d}$, therefore i. The distance D decreases, the fringe width $\beta$ also decreases if screen is moved closer to the plane of the slits.
ii. Fringe width $\beta$ decreases if separation d between two slits is increased.

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