4.3 Interference of Light

4.3 Interference of Light

Definition:

Interference is the phenomenon where two or more light waves superpose to form a resultant wave of greater, lower, or the same amplitude. Interference can be constructive or destructive depending on the phase difference between the waves.

- **Constructive Interference:** Occurs when the waves are in phase and the amplitudes add together.
- **Destructive Interference:** Occurs when the waves are out of phase and the amplitudes subtract from each other.

Young's Double-Slit Experiment:

This classic experiment demonstrates the wave nature of light through interference. When light passes through two closely spaced slits, it creates an interference pattern of bright and dark fringes on a screen.

Example Problem:

In a double-slit experiment, the wavelength of light is 600 nm, the slit separation is 0.2 mm, and the distance to the screen is 1 meter. Calculate the distance between adjacent bright fringes.

Solution:

The distance between adjacent bright fringes (fringe spacing) Δy is given by:
Δy = λD / d
where:
- λ is the wavelength of light,
- D is the distance to the screen,
- d is the slit separation.
Substituting the values:
Δy = (600 × 10⁻⁹ m × 1 m) / (0.2 × 10⁻³ m) = 3 × 10⁻³ m = 3 mm
The distance between adjacent bright fringes is 3 mm.