The spreading of a wave as it passes through a gap or around the edge of an obstacle. Diffraction explains why we can hear around corners but not see around them — sound wavelengths are comparable to doorway sizes, while light wavelengths are far too small.
Definition
The spreading of a wave as it passes through a gap or around the edge of an obstacle.
💡 Intuition
Waves 'bend around corners'—you can hear someone even if you can't see them.
🎯 Core Idea
Diffraction is significant when the opening is comparable to the wavelength.
Example
Notation
a is the slit width in metres, \theta is the diffraction angle, \lambda is the wavelength, m is the order number (nonzero integer), and I_0 is the central maximum intensity.
🌟 Why It Matters
Diffraction explains why we can hear around corners but not see around them — sound wavelengths are comparable to doorway sizes, while light wavelengths are far too small. It also governs the resolution limit of telescopes, microscopes, and cameras.
💭 Hint When Stuck
When analysing a diffraction problem, compare the wavelength of the wave to the size of the gap or obstacle. If they are similar, expect significant spreading. For single-slit diffraction, minima occur at angles satisfying a\sin\theta = m\lambda where m is a nonzero integer and a is the slit width.
Formal View
Related Concepts
🚧 Common Stuck Point
Larger wavelength = more diffraction. Radio bends around buildings; light doesn't.
⚠️ Common Mistakes
- Thinking diffraction only happens with light — all waves (sound, water, radio) diffract; it is a universal wave property.
- Confusing diffraction with refraction — diffraction is spreading through a gap or around an edge, while refraction is bending due to a change in medium and wave speed.
- Assuming a narrower slit produces a narrower diffraction pattern — the opposite is true; a narrower slit causes more spreading.
Frequently Asked Questions
What is Diffraction in Physics?
The spreading of a wave as it passes through a gap or around the edge of an obstacle.
When do you use Diffraction?
When analysing a diffraction problem, compare the wavelength of the wave to the size of the gap or obstacle. If they are similar, expect significant spreading. For single-slit diffraction, minima occur at angles satisfying a\sin\theta = m\lambda where m is a nonzero integer and a is the slit width.
What do students usually get wrong about Diffraction?
Larger wavelength = more diffraction. Radio bends around buildings; light doesn't.
Prerequisites
Next Steps
How Diffraction Connects to Other Ideas
To understand diffraction, you should first be comfortable with waves and wavelength. Once you have a solid grasp of diffraction, you can move on to interference.
🧪 Visualization Static
Visual demonstration of this concept.