9702 · 8.2
Diffraction — FAQ
Frequently asked questions for 9702 Diffraction. Direct answers first, then deeper explanation — then practise with marking.
What is the main difference between diffraction and interference?
Diffraction describes the spreading of a single wavefront when it passes through a gap or around an obstacle, essentially causing the wave to bend. Interference, on the other hand, occurs when two or more coherent waves superpose, leading to a resultant wave with varying amplitude (bright and dark fringes). Diffraction through multiple slits (like a grating) creates the conditions for interference to become observable as a distinct pattern.
Why is the central bright fringe in single-slit diffraction wider?
The central maximum is formed by light waves from all parts of the slit arriving at the screen with very little path difference, leading to constructive interference across a broader angular range. For higher-order maxima, the conditions for constructive interference are much more specific and involve cancellation from different parts of the slit, resulting in narrower and dimmer bright fringes.
Can diffraction occur with sound waves?
Yes, absolutely! Diffraction is a property of all waves. Sound waves have much larger wavelengths than visible light (typically centimetres to metres), so they diffract much more noticeably around everyday objects like doorways and corners. This is why you can hear someone speaking in another room even if you cannot see them.