Post 4: Young's Double-Slit Experiment

In the field of wave optics, Young's double-slit experiment is a fundamental experiment that demonstrates the interference of light waves and the formation of interference patterns. This experiment, performed by Thomas Young in 1801, provided strong evidence for the wave nature of light.

Experimental Setup

Young's double-slit experiment involves a light source, a barrier with two narrow slits, and a screen for detecting the light pattern. The barrier, placed between the light source and the screen, has two closely spaced slits. When light passes through these slits, interference occurs, leading to the formation of a pattern of bright and dark fringes on the screen.

Interference Pattern

The interference pattern formed in Young's double-slit experiment is a result of the superposition of two coherent sources. Coherence implies that the two sources have the same frequency, wavelength, and a constant phase difference.

When the light waves emerging from the two slits meet at the screen, they interfere constructively at some locations, resulting in bright fringes, and interfere destructively at others, leading to dark fringes. The distance between adjacent bright or dark fringes is called the fringe spacing or fringe separation, denoted by 'x'.

Formula for Fringe Spacing

The fringe spacing 'x' in Young's double-slit experiment can be calculated using the formula:

x = (λ * D) / d

Where:

• 'x' is the fringe spacing
• 'λ' is the wavelength of light used in the experiment
• 'D' is the distance between the double slits and the screen
• 'd' is the distance between the two slits

Example

Let's consider an example to understand the calculation of fringe spacing.

Suppose the experiment is performed with monochromatic light of wavelength 'λ = 500 nm'. The distance between the double slits and the screen is 'D = 2 meters', and the separation between the slits is 'd = 0.1 mm'.

Plugging these values into the formula, we can calculate the fringe spacing:

x = (500 nm * 2 m) / (0.1 mm)
x = 10 mm

Therefore, the fringe spacing is '10 mm'.

Conclusion

Young's double-slit experiment is a significant demonstration of wave interference. By observing the resulting interference pattern, we can confirm the wave nature of light and quantify the behavior of interference using the fringe spacing formula. Understanding this experiment is crucial in developing a deeper understanding of wave optics and interference in the study of light.