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Explain what is meant by the Rayleigh criterion - AQA - A-Level Physics - Question 5 - 2021 - Paper 4
Question 5
Explain what is meant by the Rayleigh criterion. The Rayleigh criterion defines the minimum angle between two objects that can be resolved by an optical system. Thi... show full transcript
Worked Solution & Example Answer:Explain what is meant by the Rayleigh criterion - AQA - A-Level Physics - Question 5 - 2021 - Paper 4
Step 1
Explain what is meant by the Rayleigh criterion
Answer
The Rayleigh criterion identifies the minimum subtended angle between two objects whose images can be resolved. The minimum angle is given by the formula:
where is the wavelength, and is the diameter of the aperture. It specifically refers to the first minimum in the diffraction pattern of one object coinciding with the first minimum of the diffraction pattern of another object.
Step 2
Explain why this telescope must be located in space.
Answer
The telescope detects wavelengths in the ultraviolet (90 nm to 120 nm), which are absorbed by the Earth's atmosphere. Consequently, a ground-based telescope would not be able to observe these wavelengths effectively. Locating the telescope in space ensures that it remains above the atmospheric interference, allowing for clear and uninterrupted observations.
Step 3
Discuss one advantage this telescope has compared to a telescope with the same aperture using visible light.
Answer
One significant advantage of using ultraviolet light is that it enables the detection of features and emissions from astronomical objects that are not observable in the visible spectrum. This allows for a greater gain in identifying and studying phenomena such as young stars and gas clouds, which emit strongly in ultraviolet wavelengths. The increased ability to collect data in these ranges can lead to a more detailed understanding of celestial objects.
Step 4
Compare the performances of the telescopes in Table 1 when both are used to see the same faint radio objects.
Answer
When comparing the Arecibo telescope with a diameter of 305 m to the Lovell telescope at 76 m, the Arecibo telescope has a significantly larger collecting area. The collecting power of a telescope increases with the square of the diameter, meaning the Arecibo telescope can collect approximately:
This leads to higher sensitivity in detecting faint radio sources. Additionally, the spherical shape of Arecibo may cause certain aberrations, while the parabolic shape of Lovell can provide higher resolution images, despite its smaller aperture.