Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.

#
Use a diffraction grating to measure two wavelengths

Your job is to use a diffraction grating
to measure two wavelengths:

- the wavelength of a red laser (again)
- the wavelength of a yellowish lamp

The first involves the same procedure you've used
in the recent past:
shine laser light through a device
and measure the separation of bright or dark
spots on a distant screen:

Set up an optics bench and laser as shown above.
Instead of shining the laser through a wheel,
shine it through a diffraction grating which
sits on an optics component carrier.
Place a piece of paper on the wall, and arrange things
so that you can mark on a piece of paper
the central bright spot and one spot to the side.
The distance **L** will probably be smaller than
you've used in the past -- perhaps 50 or 60 cm.

- Measure the separation between the central spot
and a single spot to the side.

- Make a table of your measurements, which will
be the distances
**L** and **y**.
Each value must have units and an estimate of uncertainty.

- Now, compute the wavelength of the light.
Just use a simple formula to find the wavelength.
You must also propagate the uncertainties in
your measured distances to determine the uncertainty
in this wavelength.

If all went well, your value for the wavelength of laser
light should be similar to, **but more precise than**,
your earlier measurements.

####
The wavelength of a yellowish lamp

Remove the diffraction grating from the optical bench
and hold it carefully in your hand, a few inches in front
of one of your eyes.
Look through it at the spot formed by the laser on the wall.

- What do you see?
Now, hold the grating in front of your eye
as you look at the lamp sitting on the desk
at the front of the room.

- What do you see now?

- How can you use this technique to measure the
wavelength of light emitted by the lamp?
Draw a picture to explain.

- Measure the wavelength of the yellowish light
emitted by the lamp.
Show all your measurements,
including uncertainties.
Derive the uncertainty in wavelength
of the light.

- What is the actual wavelength of this light?
Is your value consistent with the actual value,
within the uncertainty?

*Hint: Sample Problem 36-6*

Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.