Diffraction and diffraction gratingsAQA A-Level Physics: Subtopic test

1. 1
   Monochromatic light of wavelength 600 nm is directed at a single narrow slit of width 0.10 mm. The light that passes through forms a diffraction pattern on a screen several metres away.

   (a)

   Which of the following describes the pattern on the screen?

   [1 mark]

   • AEvenly spaced bright fringes of equal intensity
   • BA wide bright central maximum with narrower, much less intense maxima on both sides
   • CA single sharp bright line the same width as the slit
   • DTwo bright bands either side of a dark centre

   (b)

   The slit is narrowed to a width of 0.05 mm and nothing else is changed. What happens to the central maximum?

   [1 mark]

   • AIt becomes wider
   • BIt becomes narrower
   • CIt stays the same width but becomes dimmer
   • DIt stays the same width and brightness

   (c)

   The slit is replaced by a gap 10 mm wide. Explain why little diffraction is now seen.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Light of wavelength 589 nm from a sodium lamp is incident normally on a diffraction grating that has 600 lines per millimetre.

   (a)

   What is the spacing d of the slits of the grating?

   [1 mark]

   • A6.0 × 10⁻⁴ m
   • B1.7 × 10⁻³ m
   • C1.7 × 10⁻⁶ m
   • D6.0 × 10⁵ m

   (b)

   What is the highest order of maximum that can be observed on one side of the straight-through direction?

   [1 mark]

   • A1
   • B3
   • C4
   • D2

   (c)

   Calculate the angle between the straight-through direction and the first-order maximum.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A laser of unknown wavelength is directed at normal incidence at a diffraction grating that has 300 lines per millimetre. The second-order maximum is observed at an angle of 22.3° to the straight-through direction.

   (a)

   Calculate the wavelength of the laser light.

   [3 marks]

   (b)

   The grating is replaced by one with 600 lines per millimetre. Determine the angle of the second-order maximum and state, with a calculation, how the number of orders seen on each side of the straight-through direction changes.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A diffraction grating is a transparent plate ruled with a very large number of equally spaced parallel slits. A class uses a grating at normal incidence to study the light from several lamps, using both monochromatic light and white light.

   (a)

   Derive the equation d sin θ = nλ for a diffraction grating, where d is the slit spacing, θ is the angle to the straight-through direction of a maximum and n is the order of the maximum.

   [6 marks]

   (b)

   Evaluate the use of a diffraction grating, compared with a double slit, to measure the wavelength of light. Describe what the class would see with white light, and give one application of diffraction gratings.

   [6 marks]

   Total for question 4: 12 marks

End of questions