How does a single-dish radio telescope collect and focus radio waves?

It uses a parabolic dish reflector to collect and focus radio waves, in the same way that an optical reflecting telescope uses a parabolic mirror to collect and focus visible light.

What is the typical wavelength range detected by radio telescopes?

Radio telescopes detect electromagnetic radiation with wavelengths typically ranging from about 1 mm to several metres.

What wavelength range does an optical telescope detect?

Optical telescopes detect visible light with wavelengths of approximately 400–700 nm.

Why must radio telescope dishes be much larger than optical telescope mirrors?

Radio wavelengths are much longer than optical wavelengths, so larger apertures are required to achieve useful resolving power.

How does the collecting power of a telescope depend on its aperture?

Collecting power is proportional to the area of the aperture, so larger dishes or mirrors collect more radiation and can detect fainter sources.

State the relationship between collecting power and aperture diameter.

Collecting power is proportional to the square of the diameter of the aperture (P ∝ d²).

AQA A-Level Physics 7408

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AstrophysicsOptional topic

Topic overview Astronomical telescope consisting of two converging lenses Reflecting telescopes Single dish radio telescopes, I-R, U-V and X-ray telescopes Advantages of large diameter telescopes Classification by luminosity Absolute magnitude, M Classification by temperature, black-body radiation Principles of the use of stellar spectral classes The Hertzsprung-Russell (HR) diagram Supernovae, neutron stars and black holes Doppler effect Hubble's law Quasars Detection of exoplanets

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Astrophysics

Single dish radio telescopes, I-R, U-V and X-ray telescopes

5 things to know
Paper 3, section B

Overview

Comparing telescopes across the spectrum on resolution, collecting power and where they must be sited.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

How does collecting power depend on aperture, and why must radio dishes be so large?

Numbers

How are two telescopes' collecting powers compared, which wavebands give the finest resolution, and why must radio dishes be large?

Numbers

Why are infrared telescopes sited high up, and what alternatives exist?

Key term

Where are ultraviolet telescopes typically located?

Key term

Why can X-rays not be focused by conventional reflection at normal incidence?

Questions from this subtopic

Each one with the model answer underneath.

1
How does a single-dish radio telescope collect and focus radio waves?
Model answer
It uses a parabolic dish reflector to collect and focus radio waves, in the same way that an optical reflecting telescope uses a parabolic mirror to collect and focus visible light.
2
What is the typical wavelength range detected by radio telescopes?
Model answer
Radio telescopes detect electromagnetic radiation with wavelengths typically ranging from about 1 mm to several metres.
3
What wavelength range does an optical telescope detect?
Model answer
Optical telescopes detect visible light with wavelengths of approximately 400–700 nm.
4
Why must radio telescope dishes be much larger than optical telescope mirrors?
Model answer
Radio wavelengths are much longer than optical wavelengths, so larger apertures are required to achieve useful resolving power.
5
How does the collecting power of a telescope depend on its aperture?
Model answer
Collecting power is proportional to the area of the aperture, so larger dishes or mirrors collect more radiation and can detect fainter sources.
6
State the relationship between collecting power and aperture diameter.
Model answer
Collecting power is proportional to the square of the diameter of the aperture (P ∝ d²).

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