This java applet is a simulation that demonstrates scalar waves in two dimensions. For a more flexible applet, try the ripple tank. This applet is faster but less powerful than the ripple tank applet.

The Setup popup can be used to view some interesting pre-defined experiments. Once an experiment is selected, you may modify it all you want. The choices are:

• Single Slit: this demonstrates diffraction of waves travelling through a slit. The slit width can be controlled with the "Slit Width" slider.
• Double Slit: this demonstrates diffraction of waves travelling through a double slit. Use the "Slit Width" slider to control the slit width, and "Separation" to control the separation between them. The "Balance" slider is like the balance dial on a radio; if you put it in the middle, both slits' waves are equally strong, but if you put it off to one side, then one slit becomes stronger at the expense of the other. The "Phase Difference" slider can be used to adjust the relative phase of the waves coming through the slits.
• Multiple Slits. this shows diffraction of waves travelling through multiple slits. The number of slits can be controlled with the "Slit Count" slider.
• Obstacle. this shows diffraction around an obstacle of variable width.
• Zone Plate (Even): This creates a zone plate, which uses diffraction to focus light.
• Zone Plate (Odd): This creates another zone plate which is similar to the previous one, but has opaque areas made transparent and vice versa. It also focuses light.
• Phase-Reversal Zone Plate: Instead of opaque areas, this zone plate has areas which retard the incoming wave by half a wavelength.
• Blazed Zone Plate: This zone plate has areas which retard the incoming wave by just the right amount.
• Absorption Hologram: This is a hologram which uses absorption to create a holographic image. The image created is very simple; it consists of two point sources. You can control the location of the two sources with the X1, Y1, X2, and Y2 sliders.
• Phase Hologram: This is a hologram which uses phase delay to create a holographic image.

The Show Intensity checkbox determines whether to show the wave intensity, or the waves themselves. When this is unchecked, the positive wavefronts are shown in green, and negative in red. Viewing the waves (instead of the intensity) only works well when zoomed in, using a low frequency; otherwise the individual waves are too small to see.

The Stopped checkbox stops the applet, in case you want to take a closer look at something, or if you want to work on something with the mouse without worrying about it changing out from under you.

The Alternate Rendering checkbox is used to speed up rendering, but it actually slows things down on some machines.

The Tri-Chromatic checkbox will cause the light source to emit red, green, and blue light. These three colors have different wavelengths, which means they generate different diffraction patterns. The applet will generate the three patterns and combine them to create a color image. This checkbox makes the images a lot more interesting but it also slows things down a bit. It only works when the Show Intensity checkbox is checked.

The Reset Time button clears any waves on the screen and starts a new wavefront starting from the source. This only works when Show Intensity is not checked.

The Incidence Angle slider controls the angle of the incoming wave.

The Speed slider controls how far the waves move between frames.

The Zoom Out slider zooms out when you slide it to the right. This slows things down quite a bit.

The Resolution slider allows you to speed up or slow down the applet by adjusting the resolution; a higher resolution is slower but looks better. Also, increasing the resolution acts like zooming out.

The Source Frequency slider controls the frequency of the source.

The Brightness slider controls the brightness, just like on a TV set. This can be used to view faint waves more easily.

Click here to go to the applet.