Diffraction Gratings

Question 1

What is diffraction?

Answer 1

The spreading out/bending of waves as they pass through a gap or obstacle

Question 2

What is coherent light?

Answer 2

Has a fixed relationship and a fixed wavelength

Question 3

How does a diffraction pattern appear on a screen?

Answer 3

• Light passes through the slits in the diffraction grating
• As the light passes through it spreads out by diffraction
• The light waves interfere with each other as they cross over
• The greater the wavelength the bigger the change in direction as they pass through the slit
• A smaller slit separation gives a greater diffraction

Question 4

Bright points (maximum)

Answer 4

• At the screen, the light is in phase
• We get constructive interference
• A peak meets a peak/trough meets a trough
• Central maximum is always the brightest
• The maxima gets dimmer as you move away from the centre

Question 4

Dark points (minimum)

Answer 4

• At the screen, the light is 180 degrees/half a wavelength out of phase
• The distance between the screen and the slits gives a path of half a wavelength
• A peak meets a trough
• We get destructive interference