# Homework Help: Triple-slit interference

1. Jul 15, 2007

### patapat

I'm having a bit of trouble with this problem:

Three slits of negligible width are cut into points y=-d,0,d on a screen. A second screen is placed parallel to the first a distance L(L>>d) away. Light is projected through the slits onto the screen, forming an interference pattern. Express the intensity of the pattern in terms of L, d, lamda, I_0 (the intensity of each beam individually), and the height h along the screen.

I'm not sure exactly how similar this triple slit experiment would be compared to the more common double-slit experiments. I would appreciate it if the differences between the two were explained. Thanks in advance for any and all responses.

2. Jul 15, 2007

### meopemuk

Here are some ideas. Take a point point x on the second screen and denote d1, d2, d3 shortest distances from x to the three slits. Assume that external light arrives to all three slits with the same phase, then the amplitudes of light arriving at the point x and passed through slits 1, 2, and 3 will be proportional to $sin (2 \pi d_1/ \lambda)$, $sin (2 \pi d_2/ \lambda)$, and $sin (2 \pi d_3/ \lambda)$, respectively. Then in order to find the light intensity at the point x you should calculate a square of the sum of these three terms and multiply this square by an appropriate intensity factor.

3. Jul 16, 2007

### patapat

That makes sense, but I'm not exactly sure what u mean by light intensity factor.