Diffraction

Overview

Single slit diffraction, the grating equation and its derivation, and the orders of maxima.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Describe the diffraction pattern produced when monochromatic light passes through a single slit.

   Model answer

   A bright central maximum with alternating dark and bright fringes of decreasing intensity on either side.

2. 2

   When white light passes through a single slit, what colour is the central maximum and why?

   Model answer

   The central maximum is white because all wavelengths overlap at the centre where the path difference is zero.

3. 3

   In the subsidiary maxima of a white light single-slit diffraction pattern, which colour appears on the outer edges and which on the inner edges?

   Model answer

   Red appears on the outer edges and blue/violet on the inner edges, because longer wavelengths diffract through larger angles.

4. 4

   How does increasing the wavelength of light affect the width of the central diffraction maximum from a single slit?

   Model answer

   The width of the central maximum increases.

5. 5

   What happens to the width of the central diffraction maximum when the slit width is decreased?

   Model answer

   The width of the central maximum increases.

6. 6

   Define a plane transmission diffraction grating.

   Model answer

   A large number of equally spaced parallel slits.

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