Question

For multiple slit interference (a pair of slits instead of double slits):

1) Does the distance between maxima change when you change the slit width?

2) How does the distance to the first maximum of the diffraction envelope change with slit widths?

3) Predict what would happen if we used white light (light with all wavelength) instead of just a monochromatic (one wavelength) light source?

Answer 1

The governing formula for multiple slit interference is

where

wavelength

distance to the screen

slit width.

fringe width

Question 1

When the slit width is changed, the fringe width, which is also the distance between maxima, will change.

As they are inversely proportional, increasing the slit width decreases the distance between maxima, and decreasing it increases the distance between maxima.

Question 2

The distance to the first maximum remains constant, as its position is un altered by slit width.

Question 3

Since the fringe width is dependent on the wavelength, white light, being a mixture of lights, would give an interference pattern consisting of multiple wavelengths having fringes of different width.

The longer the wavelength, the wider the fringe.