Fortunately, we don't have to have expensive lasers to perform this type of experiment.   A coherent light source can effectively be achieved by replacing the laser with a bright light, a filter and a single slit. Click here to find out more details.

In this experiment, you will measure the wavelengths of red, yellow, green and blue light.  To do this:

• Firstly select a filter color.

• Measure D by pressing the mouse over the tape measure and 'dragging' the tape horizontally along to the white screen.  Record D in the results data sheet.

• Now set the slit separation, s, and width, b, to your liking and make a note of s in your datasheet.   Note the effect of b on the fringes.  Click here to find out more details.

• Measure the fringe width, w.   Click on the grey vernier scale on the RHS to move the travelling microscope.   Use the "Up" and "Down" buttons for finer adjustments.   (Alternatively, click on the diagram and then use the four arrow keys on your keyboard to the same effect).

• Measure the distance across a number of fringes.  Calculate the single fringe width, w from this.

• Finally, calculate l for this colour using the Young's double slit formula:

Click here  for the derivation of this formula.

• Repeat for the other three colours.