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Q1-3. These questions are about the resolution of stars:

1. Which of these descriptions best explains what is meant by the "resolution of stars"?

  • A. Being able to identify the temperature of a star.
  • B. Being able to distinguish 2 stars that are close together when looking at an image.
  • C. Identifying the distance to stars.
  • D. Identifying the radius of a star.

2. Light passes through the telescope which acts as an aperture. Which physical effect limits the resolution of stars?

  • A. Dispersion as light passes through the aperture.
  • B. Diffraction as light passes through the aperture.
  • C. Refraction as light passes through the aperture.
  • D. Interference as light passes through the aperture.

3. To make it easier to resolve stars, different frequencies of light could be used, or a wider or smaller aperture. Which of these changes will make it easier to resolve stars?

Frequency of light size of aperture
higher larger
higher smaller
lower larger
lower smaller


4. The formula use for resolution includes the constant "1.22". This constant is required for...

  • A. circular apertures
  • B. rectangular apertures
  • C. square apertures
  • D. all apertures


5. Which of the following graphs shows the single slit diffraction patterns of 2 sources that are just on the limit of being resolved?


6. A car in the distance has 2 headlights. A student takes a picture of the car through a camera using visible light. On the image, there is only one light source visible.

Which of the following will NOT make it easier to resolve the car headlights?

  • A. Move closer to the car to take the image.
  • B. Make the camera lens larger.
  • C. Increasing the intensity of the headlights.
  • D. Use an ultraviolet camera of the same design.


7-10. Diffraction gratings can be used to resolve different frequencies of light. The formula used is given here:

R = λ/Δλ = mN

7. Which of these statements about the resolvance R is correct?

Two wavelengths of light from the same source are easier to distinguish apart if..

  • A. R is low and Δλ is low.
  • B. R is high and Δλ is low.
  • C. R is low and Δλ is high.
  • D. R is high and Δλ is high.

8. A sodium lamp produces two spectral lines that are very close together:

  • λ1 = 589.00 nm
  • λ2 = 589.59 nm

This gives a value of resolvance of approximately:

  • A. 100
  • B. 100 nm
  • C. 1000
  • D. 1000 nm

9. What do the letters N and m in the resolvance formula represent?

m N
total number of slits order of the diffraction
order of the diffraction total number of slits
number of slits illuminated order of the diffraction
order of the diffraction number of slits illuminated


10. A very small diffraction grating can produce an interfernce pattern up to the 6th order of diffraction. All 100 lines in the grating are illuminated.

Two narrow spectral bands are centred on a wavelength of 6000 nm. What is the value of Δλ that can be resolved with this grating?

  • A. 0.1 nm
  • B. 0.01 nm
  • C. 10 nm
  • D. 100 nm