Diffraction of polychromatic light
If we use light that’s made up of multiple wavelengths (for example, white light), we’ll see a pattern of coloured fringes instead of just bright and dark fringes.
White light
The central fringe will be white, because all of the wavelengths will interfere constructively at the centre.
The fringes on either side of the central fringe will be coloured, because the different wavelengths will interfere constructively at different points on the screen.
Colour of the fringes
Closer to the centre, the fringes will be blue and violet, because the shorter wavelengths will interfere constructively closer to the centre.
Further away from the centre, the fringes will be red and orange, because the opposite (longer wavelengths will interfere constructively further away from the centre).
flashcards
| Question | Answer |
|---|---|
| What happens when polychromatic light (e.g., white light) is diffracted? | We see a pattern of coloured fringes instead of just bright and dark fringes. |
| What colour is the central fringe when white light is diffracted, and why? | White, because all wavelengths interfere constructively at the centre. |
| Why are the fringes on either side of the central fringe coloured in white-light diffraction? | Different wavelengths interfere constructively at different points on the screen. |
| Which colours appear closer to the centre in a white-light diffraction pattern? | Blue and violet (shorter wavelengths interfere constructively closer to the centre). |
| Which colours appear further from the centre in a white-light diffraction pattern? | Red and orange (longer wavelengths interfere constructively further from the centre). |