PAG 05.4 Determining Wavelength Using Diffraction From A CD

Question 1

What equation relates wavelength of a light source to the angle of diffraction?

Answer 1

wavelength= d sin(theta)
wavelength = diffraction grating spacing x sin(angle from centre)

Question 2

What happens to light as it passes through a slit?

Answer 2

Light diffracts as it passes through a slit, with the maximum diffraction occurring when the slit spacing matches the light’s wavelength

Question 3

Describe the diffraction pattern observed from the CD reflection

Answer 3

The pattern is a series of coloured concentric circles with red on the outside and violet on the inside

Question 4

What procedure is carried out to get the required frequency of light on the edge of the CD?

Answer 4

The CD is moved relative to the eye until the circle of the required frequency of light sits on the diameter of the CD

Question 5

What two measurements are recorded?

Answer 5

Distance of the eye to the CD (D)
Radius of the CD (r)

Question 6

How can the angle of diffraction be determined from these two measurements?

Answer 6

tan(angle)=r/D

Question 7

How can the wavelength of light be calculated?

Answer 7

wavelength=d x sin(angle)
use calculated angles and diffraction pattern spacing

Question 8

How can uncertainty in these values of wavelength be found?

Answer 8

By comparing them to the accepted value of wavelength for coloured LEDs