Wave Interference

Fringe Width in Double-Slit Interference

The fringe width in a double-slit interference pattern is given by the formula:

Here, the wavelength is directly proportional to the fringe width .

- Red light has a wavelength of approximately 700 nm.
- Violet light has a wavelength of approximately 400 nm.

To compare the fringe widths:

Substituting values:

This means the fringe width for red light is about 1.75 times that of violet light.

Since none of the given answer choices (A, B, C, D) match this exactly, the closest option is (D) "double", suggesting that the fringe width of red light is nearly twice that of violet light.

The phenomenon of diffraction is responsible for the colored bands observed when a compact disc (CD) is illuminated by a small source of white light. Diffraction occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength. In the case of a CD, the surface of the disc contains a series of closely spaced microscopic grooves or tracks. When white light illuminates the CD, these grooves act as diffracting elements.

The diffracted light waves interfere with each other, resulting in both constructive and destructive interference. This interference causes different wavelengths (colors) of light to be reinforced or canceled out at different angles, creating the observed colored bands on the CD surface. Therefore, the correct answer is diffraction.