# Physics, Single Slit Diffraction Concepts?

An experiment is conducted in which red light is diffracted through a single slit. Then, each of the following alterations to the original experiment is made, one at a time, and the experiment is repeated. After each alteration, the experiment is returned to its original configuration.

A The slit width is halved.

B The distance between the slits and the screen is halved.

C The slit width is doubled.

D A green, rather than red, light source is used.

E The experiment is conducted in a water-filled tank.

F The distance between the slits and the screen is doubled.

Which of these alterations decreases the angles at which the diffraction minima appear?

• The relevant equation is

d*sin(theta) = m*lambda

where d is the slit width, theta is the angle of the maximum (I know you asked about minima, but when the angles for minima decrease, so do those for maxima, so it is irrelevant), m is the order of the maximum (first, second, etc.), and lambda is the wavelength of the light.

First, let’s solve for theta:

theta = arcsin( m*lambda / d )

as the argument of the arcsin increases, so does theta, so:

A

If d is halved, the argument increases, and theta does too

B

This is irrelevant, as the distance to the screen does not affect the angle at all, just the width on the screen

C

theta decreases (see A)

D

This amounts to decreasing lambda, so theta decreases

E

This is kinda tricky, but not really. In water, the light’s frequency stays the same, but it slows down, so the wavelength gets smaller. So, as with C, theta decreases.

F

Irrelevant (see B)

Hope this helps!