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# 4.1: Background Material

## Play with this Simulator!

Go ahead and run this PhET simulator in another window. This software simulates wave interference of various types. In the lab, we will be focusing on interference of EM waves passing through a double slit. To prepare for this, you should therefore configure the simulator as follows:

• select the window "Slits"
• click the light source button
• select the "Screen" check box, and the "Intensity" sub check box
• select "Two Slits" in the drop-down menu
• leave the "Amplitude" slider at its "max" setting
• use the "Frequency" slider to adjust the frequency (wavelength) of the light
• use the "Slit Separation" slider to change the double slit

The green button on the Light Generator starts a plane wave, represented by alternating bright and dark regions that represent the crests and troughs of the waves, respectively. [Note that these do not represent bright and dark regions! That is, if you were in the simulator, and you looked at the Light Generator, you would see constant, uniformly-bright red light coming from it. If you run the simulator, this is in fact what you see on the screen.]

In particular, you want to explore the effect of changing the wavelength of the light and changing the slit separation for a fixed wavelength, as these are things we will be doing in the lab.