Physics
Diffraction
Quick fact
Diffraction is why a CD or DVD creates a rainbow pattern: the tiny grooves act like a diffraction grating, splitting white light into its colors.
Why this is interesting
Have you ever noticed that sound travels around a corner, allowing you to hear someone in another room, but light from that same person is blocked? That's diffraction at work—showing that both light and sound are waves that can bend around obstacles.
Read the full explanation
Understanding Diffraction
Imagine dropping a pebble into a still pond. The ripples spread in circles. If you place a small barrier in the water, the ripples bend around its edges. This bending is diffraction. The same happens with sound: when you stand around a corner, sound waves bend to reach your ears. Light also diffracts, though the effect is tiny because light has a very short wavelength. When light passes through a narrow slit or around a sharp edge, it spreads out. The narrower the slit, the more the light spreads. This is why a pinhole camera produces a fuzzy image—the light diffracts as it passes through the tiny hole.
A deeper explanation
Diffraction arises because every point on a wavefront acts as a source of new spherical waves (Huygens' principle). When a wavefront encounters an obstacle, the secondary waves from the edges constructively and destructively interfere, creating a pattern of alternating bright and dark bands (the diffraction pattern). The amount of bending depends on the ratio of the wavelength to the size of the obstacle or aperture: larger wavelengths diffract more. For light, this explains why we can resolve fine details only up to a limit—the diffraction limit—which constrains the maximum resolution of microscopes and telescopes. In everyday life, diffraction limits the sharpness of camera images and the clarity of audio signals. It is also the basis for technologies like diffraction gratings used in spectrometers to analyze light spectra.