Lab 10: Wave opticsOnly 2 more labs to go!!

Light is an electromagnetic wave. Because of the wave nature of light it interacts differentlythan you might expect. Consider the following situation:

light rays

double slits screen

screendouble slits

Wave frontfrom light

lightsource

screendouble slits

intensitymaxima

d

R1

R2

The maximas in intensity occur whenthe difference in path (from the twoslits) is equal to an integral number of wavelengths. In other words, when:

nR It can be shown from trigonometrythat,

sindR

D

So then we will have points of maximumswhen:

nd sin

Notice that for small angles, < 5o, sin = tan , and for this situation tan is:

Where d, is the slit separation, is the angle between the maxima and the optical axis, n is the order of intensity (i.e. n = 1, 2 3, ..etc.), and is the wavelength of light.

D

ytan

y

where, y is the distance the maxima is from the central maxima, and D is the distance between the screen and the grating.

centralmaxima

So our equation becomes:

d

Dnyn

D

yd

nd

sin

Today, you are going to measure the distance spots occur from the central maxima. From this you will be ask to calculate the slit separation and the wavelength. Let’s look at thisexample:

White light is incident upon a regular array of slits. An interference pattern is observed ona screen, a distance of 8 meters from the slits. It is noted that the second order yellow ( = 550 nm)is at a horizontal distance of 10 cm from the center.

What will be the location of the first order yellow?

d

mm

d

Dny

91055018

Unfortunately, we don’t have the slit separation so we need to solve for d, first.

Remember that the second order spot is found 10cm away from the center, so we can use this information to calculate d:

m

m

mm

y

Dnd 5

9

108.81.0

1055028

Using this we can solve for y and we get:

y = 0.05 m