Question

What is fringe in wave optics?

Answer 1

Interference

Interference is the phenomenon in which two or more waves superpose to form a resultant wave of greater, lower, or the same amplitude.

There are two types of interference

Constructive Interference

1. When two waves travel in the same direction and are in phase with each other, their amplitude gets added, and the resultant wave is obtained. Here, the waves are said to have undergone constructive interference.
2. When a crest of one wave meets a crest of another wave of the same frequency, then the resultant amplitude is the sum of the individual amplitudes of the waves.
3. We can also observe that the amplitude of the resultant wave is higher than the waves which undergo interference.
4. Constructive interference occurs when the phase difference between the waves is an even multiple of π (180°).

Destructive Interference

1. When two waves of different phases meet, their resultant amplitude decreases is called destructive Interference
2. The resulting amplitude of the wave, which undergoes destructive interference, is equal to the difference in the individual amplitudes of the waves.
3. This type of interference occurs when the difference is an odd multiple of π.

According to the diagram in sodium light the red and yellow patterns are fringes and in white light the coloured and white patterns are fringes.

1. Fringe is the alternating light and dark band that forms as a result of interference.
2. The formula is used to calculate the fringe width
   $\mathrm{\beta }=\frac{\mathrm{\lambda D}}{d}$
   Where, $\mathrm{\beta }$ represents the bandwidth, $\mathrm{\lambda }$ represents wavelength of the light,$\mathrm{D}$ represents the distance between the source and the screen, $\mathrm{d}$ represents distance between the two slits
3. Young's double slit experiment helps us to find fringe width from a coherent source of light.
4. When two light waves gets superposed then constructive and destructive interference occurs.
5. Constructive interference causes the bright fringes, while destructive interference causes the dark fringes.