Question

1a. If you had a double slit, with a spacing, d, and a width, a, the pattern would have a minima from both the double slit locations and the single lit locations. If d = a/2, sketch the expected pattern.

1b. What happens to the single slit minima for diffraction gratings?

Answer 1

Intensity maxima from the double slit occur as

m? = dSin(p) ,d is the spacing between the slits.

Diffraction pattern from the slit of width a occurs as

? = aSin(p)

inteference minima of order m would coincide with the first diffraction minima of first order

then

m =d/a, given d = 2a

m=2

there will be 3 interference maxima inside the diffraction envelope as shown below.

In grating the slits are very close and the maxima become sharper with large number of slits.The minima spreads over as the light from one slit is always out of phase with light from another slit.