Diffraction - 'Double-Slit' Experiment

Introduction

• The 'Double-Slit' experiment is a classic demonstration of wave behaviour and diffraction, showcasing the interference pattern created by waves passing through two slits.
• This experiment is applicable to various types of waves, including light and sound waves.

Interference Pattern

• When waves pass through two closely spaced slits, they create an interference pattern on a screen or detector placed behind the slits.
• This pattern consists of alternating bright and dark regions, resulting from constructive and destructive interference of the waves.

Two Coherent Sources

• In the 'Double-Slit' experiment, the two slits (S1 and S2) act as coherent sources of waves.
• Coherent sources produce waves with a constant phase relationship, meaning their wavefronts align in time.

Wave Detector

• A wave detector, such as a screen or a detector device, is positioned to capture the interference pattern.
• This detector can be moved across the pattern to identify points of constructive and destructive interference.

Constructive and Destructive Interference

• Constructive interference occurs at points where waves from the two slits are in phase, resulting in an enhanced, bright region on the detector.
• Destructive interference happens at points where waves are out of phase, leading to reduced or dark regions on the detector.

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Diffraction - 'Double-Slit' Experiment

Application to Visible Light

• In the context of visible light, a screen is commonly used to display the interference pattern.
• The screen captures the interference pattern at the same plane as the screen itself.

Formula and Calculation

• The positions of constructive interference (bright fringes) and destructive interference (dark fringes) can be calculated using the following formula for constructive interference:

d * sin(θ) = m * λ

• Where:
  • d is the distance between the slits (S1 and S2).
  • θ is the angle of observation.
  • m is the order of the fringe (1, 2, 3, ...).
  • λ is the wavelength of the incident wave.

Summary

• The 'Double-Slit' experiment demonstrates the interference pattern created when waves pass through two closely spaced slits.
• It showcases the concepts of constructive and destructive interference.
• The experiment is applicable to various types of waves, including visible light.
• Understanding the interference pattern helps us explore wave behaviour and diffraction phenomena.