Diffraction
Waves spread when passing gaps or edges.
About this topic
Diffraction is the spreading out of waves as they pass through a gap or around an obstacle. It is most pronounced when the gap is about the same size as the wavelength. This is why you can hear around a corner while you can't see around it: sound waves have wavelengths of metres, light only about 500 nanometres.
A narrow gap acts like a new point source, sending out circular wavefronts, while a wide gap lets most of the wave pass straight with only slight spreading at the edges. Long-wavelength radio waves bend around hills, which is why AM radio works in valleys, whereas short-wavelength microwaves need line of sight.
Worked example: in a ripple tank with 2 cm wavelength waves, a 2 cm gap gives strong semicircular spreading, but a 20 cm gap gives only slight bending at the edges. For light and a 0.1 mm slit, the spreading is enough to make a visible pattern of bright and dark bands on a distant wall.
Diffraction limits how sharply telescopes and microscopes can see details, and it is the reason a CD shows rainbow colours. Diffraction gratings split light to analyse star composition. A misconception is that diffraction happens only at tiny holes; every wave diffracts at any edge, but it is only noticeable when the sizes are comparable.
Key ideas
- Biggest when gap ≈ wavelength
- Explains hearing around corners
- Light diffracts too
Quick check
Use cases: where Diffraction helps
- Homework: review the key idea behind Diffraction before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Diffraction without notes.
- Visual learning: play with the interactive lab to see how Diffraction changes when you adjust its inputs.
- Teaching a friend: explain Diffraction in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Diffraction?
Waves spread when passing gaps or edges.
What will I learn in Diffraction?
Biggest when gap ≈ wavelength. Explains hearing around corners. Light diffracts too.
Is Diffraction part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Diffraction lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Diffraction?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.