8.5 Observing the Universe
9 exam questions worth 25 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which type of telescope uses a curved mirror to focus the light?
Choose one answer.
Correct Not quite: the answer is A reflecting telescope
Mark scheme
B: A reflecting telescope
Model answer
A reflecting telescope (B).
State two advantages of a reflecting telescope compared with a refracting telescope.
Mark scheme
mirrors can be made much larger (1); mirrors can be supported from behind, and are lighter / do not have the colour problems of lenses (1)
Model answer
A mirror can be made much larger than a lens, and it can be supported from behind so it does not sag.
Explain why a larger telescope can detect fainter objects.
Mark scheme
it has a larger area to collect radiation (1); so it collects more of the faint light from the object (1)
Model answer
A larger telescope has a bigger area, so it collects more radiation from a faint object.
State why X-ray telescopes have to be placed on satellites.
Mark scheme
the atmosphere absorbs X-rays (1); so they cannot reach telescopes on the ground (1)
Model answer
The Earth's atmosphere absorbs X-rays, so they must be detected above the atmosphere.
Name two types of electromagnetic radiation that reach the ground from space, and two that do not.
Mark scheme
reach: radio waves and visible light (1 + 1); do not reach: any two from ultraviolet, X-rays, gamma rays (1 + 1)
Model answer
Radio waves and visible light reach the ground. Ultraviolet and X-rays are absorbed by the atmosphere.
Give two reasons why optical telescopes on the ground are built on high mountains in dry areas.
Mark scheme
less atmosphere above, so less distortion and absorption (1); fewer clouds and less water vapour / less light pollution (1)
Model answer
There is less atmosphere above the telescope, so there is less distortion and absorption. The air is also drier and clearer, with less light pollution.
Describe two ways in which telescopes have improved since the time of Galileo.
Mark scheme
any two from: larger mirrors / reflecting telescopes (1); digital detectors (CCDs) and computers (1); telescopes for other wavelengths such as radio and X-ray (1); telescopes in space (1) — each with an explanation (1 each)
Model answer
Telescopes now have much larger mirrors, which collect more light, and digital detectors with computers that make the images clearer. Telescopes in space can detect wavelengths that are absorbed by the atmosphere.
Explain why astronomers observe objects using different parts of the electromagnetic spectrum.
Mark scheme
different wavelengths give different information (1); e.g. infrared can show star formation / pass through dust (1); X-rays can show black holes / very hot gas (1)
Model answer
Different wavelengths show different things. For example, infrared passes through dust and shows where stars are forming, and X-rays show very hot objects such as material falling into black holes.
Evaluate the advantages and disadvantages of placing a telescope in space rather than on the ground.
Mark scheme
advantages: above the atmosphere so no absorption of UV, X-rays, gamma rays and infrared (1); no blurring or twinkling from the moving air (1); no clouds or light pollution (1); disadvantages: very expensive to launch (1); difficult or impossible to repair or upgrade (1)
Model answer
A space telescope is above the atmosphere, so it can detect wavelengths that are absorbed by it, and its images are not blurred by moving air, clouds or light pollution. However, it is very expensive to build and launch, and it is hard to repair or upgrade.
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