What do typical diffraction patterns looks like?
This is the diffraction pattern for RED LIGHT as it passes through a very small single slit.

This image would appear on a screen.

Note the central band of RED LIGHT, with dark bands on the side.

This is the diffraction pattern for BLUE LIGHT as it passes through a very small single slit.

Note that the bands are closer together showing lesser diffraction than in the case of the red light.

Blue has a smaller wavelength, and hence there is a lesser diffraction.

What equation do we use to perform DIFFRACTION calculations?

- the
**angle** is shown in the diagram

The **angle** is measured from the CENTRE of the CENTRAL BAND to the DARK BAND
**m** indicates which dark band you are measuring to

If, as in the diagram, then m = 1

If the second dark band is used, then m = 2
**lambda** is the wavelength of the light being used
**a** is the width of the slit through which the light is shone

The slit **a** is by the **angle**.

### Example 1

A light beam L is shone through the single slit a of width 1,13 x 10^{-4}m.

The diffraction pattern is formed on the screen which is placed 0,3m away from the slit.

The width of the entire central band (YZ) of light is 4mm.

**1.1.** What is the distance from the central band to the first dark band (XY)?

2mm (0,002m)
**1.2.** Calculate the value of the angle ?

**1.3.** Calculate the wavelength of the light.

**1.4.** Red light has a frequency range from 4,8 x 10^{14}Hz to 3,8 x 10^{14}Hz.

Prove that the light used in the above diffraction experiment is red light.

This frequency is between the given range, hence it is red light.