The Diffraction Grating explored...

This simulation allows you to experiment with the key parameters that affect the appearance of the screen fringes.

You may need to adjust the brightness and contrast controls on your monitor to optimise the effect.

• Use the "Show 'constructor' waves" box to show/hide the constructor waves.  For now, make sure the box is checked - i.e. the waves are visible.  Now try the following:

• Change the wavelength to see how it affect the screen fringes.

• Select a wavelength that gives yellow light (this is easiest to see on a computer monitor).  Select single slit diffraction conditions.  Change the slit width to see how it affects the screen fringes.  You should a bright central fringe (zero order) and also faint first (and possibly even second) order fringes.

• Now change your settings to produce 2 narrow slits.  Notice how the slit width determines the "envelope" wave.  Which parameter(s) determine the individual fringe separation?

• What happens to the second order fringes when the slit separation is exactly double the slit width?  What happens to the third order fringes when the slit separation is exactly triple the slit width?   Do you notice a pattern?

• Hide the 'constructor' waves and increase the number of slits to see how this affects the screen fringes and waveforms.

• Try the following settings:

Wavelength = 575 nm,
Screen distance = 1 m,
Slit width = 2.0e-5 m,
Slit separation = 10.0e-5 m,
Number of slits = 50,
Show 'constructor' waves = checked (visible).

The 1st and 3rd order fringes appear to be very weak.  Is this a genuine effect or one caused by the computer, do you think?  Try changing the screen distance to 2 m.