Interference (Double Slit) Calculator

Young’s Double-Slit Experiment

The double-slit experiment, first demonstrated by Thomas Young in 1801, is one of the most famous experiments in physics. It shows that light behaves as a wave, producing bright and dark fringes on a screen due to constructive and destructive interference.

The Formula

Δy = λL / d

Where:

• Δy = fringe spacing on the screen
• λ = wavelength of light
• L = distance between slits and screen
• d = distance between the two slits

Constructive and Destructive Interference

- Constructive interference: Occurs when the path difference is an integer multiple of the wavelength, creating bright fringes.
- Destructive interference: Occurs when the path difference is a half-integer multiple of the wavelength, creating dark fringes.

Worked Example

Suppose monochromatic light of wavelength 600 nm passes through two slits separated by 0.5 mm. If the screen is placed 2 m away, the fringe spacing is:

Δy = (600 × 10⁻⁹ × 2) / (0.5 × 10⁻³) = 2.4 × 10⁻³ m

So the fringes are 2.4 mm apart on the screen.

Applications

• Wave nature of light: Demonstrates that light is a wave, not just particles.
• Quantum mechanics: The experiment also applies to electrons, neutrons, and even large molecules.
• Optical instruments: Helps design interferometers and precision measurement tools.
• Coherence studies: Used to measure spatial and temporal coherence of light sources.

Insights

The double-slit experiment is often called the "most beautiful experiment in physics." It bridges classical wave theory with modern quantum mechanics, illustrating how fundamental principles of interference apply universally to waves and particles alike.