1. Measuring the wavelength of light with a diffraction grating You will need the following equipment: DC power supply & 2 leads 1 small LED board, with red, green and blue LEDs 2 metre rulers 3 clamp stands A small piece of blu tack A diffraction grating 2 x 30cm rulers A pencil

2. Measuring the wavelength of light with a diffraction grating 1.Fix the LED board firmly to the desk, and connect it to the PSU. Turn the potentiometer anticlockwise as far as it will go. 2.Secure the diffraction grating in a clamp and stand, and place it 2 - 3m from the LED board. Make a note of the exact distance “D”. 3.Clamp 2 metre rulers so they are both centred on the LEDs and extend either side of the LED board. 4.Turn on the power supply and slowly turn the potentiometer until the red LED is producing a reasonable output. 5.Observe through the diffraction grating. Ask your partner to move a pencil along the metre ruler until it is in line with the first fringe. 6.Record the position of the first fringe in the table given. Repeat for the 2 nd, 3 rd, 4 th and 5 th fringe.

3. Measuring the wavelength of light with a diffraction grating 7.Plot a graph of “d(x/L)” against “n” for each LED. 8.Calculate the gradient of each graph to find the principal wavelength produced by the LED.