IB Physics Diffraction

This tutorial sheet is about diffraction, a concept that is sometimes misunderstood.

1. State the definition of diffraction.
2. Why does diffraction occur when light passes through a single slit?
3. Explain qualitatively the pattern that we see when light passes through a single slit if i. the slit width is much greater than the wavelength ii. the slit width is much less than the wavelength.
4. Divide a single slit of width b into two sections. By considering a ray from the top of each section, show that destructive interference occurs when b sin𝜃 = 𝜆. Do this with four sections in the slit and show that destructive interference occurs when b sin𝜃 = 2𝜆. This can be generalized to b sin𝜃 = n𝜆, n=1,2,..
5. When light is now incident normally on a diffraction grating what does the equation d sin𝜃 = n𝜆, n=0,1,2,3.. predict?
6. The incident monochromatic light is not normal to the grating. Can we use the equation d sin𝜃 = n𝜆 in this situation?
7. In question 6 the angle of incidence of the light on the grating is ϕ. Show that the angle 𝜃 to the normal to the grating where intensity maxima occur are given by d ( sin(𝜃 - ϕ) - sinϕ ) = n𝜆.
8. Describe the difference between primary maxima and secondary maxima.
9. Describe the interference pattern when white light is incident normally on a diffraction grating.