 ### Diffraction 3

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 10-4m.
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 1014Hz to 3,8 x 1014Hz.
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.