Practical 12 - Determintion of wavelength using a diffraction grating

Question 1

How can we determine wavelength using a diffraction grating?

Answer 1

Measure the angle theta
Use the spacing between the lines in a diffraction grating (usually specified or can be found from the grating ruling)
Input it into the diffraction grating equation

Question 2

How do we determine the spacing between the lines in a diffraction grating?

Answer 2

Usually specified, or can be found from the grating ruling

Question 3

How do we determine the value of θ?

Answer 3

Tan θ = x
—
D

Question 4

What’s the hazard in this practical?

Answer 4

Laser

Question 5

What’s the risk with using a laser?

Answer 5

Eye damage

Question 6

What’s the control measure for using a laser in order to avoid eye damage?

Answer 6

Only switch it on when pointing it at a screen

Question 7

What should you wear when working with lasers and under which conditions?

Answer 7

Laser goggles if the laser could reflect

Question 8

Why did we not have to wear laser goggles?

Answer 8

The laser couldn’t reflect off of polystyrene, the material used for our backboard

Question 9

What are the steps to this practical?

Answer 9

Measure x for each order
Work out θ (using the tan θ = x/D equation)
Work out the wavelength at each order (using the diffraction grating equation)
Calculate the mean wavelength

Question 10

How do we determine the uncertainty for our measurement of the wavelength?

Answer 10

It’s from a spread of data, so…

max - min
——————
2