Exploring the Cosmos - Degree Exam 2010 - Mapping the Universe
1. A reflective diffraction grating is separating the light colours and creates a spectrum. What happens if the incoming light is changed from blue to red?
Nothing. Diffraction is wavelength-independent.
The angle between the diffraction orders becomes larger.
The red light is transmitted through the grating because only blue light is scattered.
The outcoming light stays blue.
2. Which statement is wrong?
The energy of photons is just dependent on the frequency.
Light has a constant speed in vacuum.
Light travels with different speeds depending on the material.
Light travels always with a constant speed.
3. Why are most of the modern telescopes for visible light reflecting telescopes?
Mirrors are easier to make and to mount.
They have no aberration.
It is not possible to melt enough glass to fabricate a large lens.
Lenses cannot be used for visible light.
4. Why are astronomers interested in different parts of the spectrum?
The results would otherwise interfere destructively.
The different colours are nice.
Different parts of the spectrum contain different information.
At some locations at the sky certain detectors do not work.
5. A Cassegrain telescope may have a focal length of 100 cm. The diameter of the mirror shall be 25 cm. The eyepiece used in this configuration has a focal length of 1 cm and a diameter of 0.5 cm. What magnification is achieved?
A magnification of 50.
A magnification of 100.
A magnification of 25.
It is not possible to calculate the magnification with these parameters.
6. Why is the colour of the sun during sunset red?
The sun changes its colour in 24 h from blue to red and back to blue.
The refraction of light is different. Blue light is more strongly refracted.
The diffraction of light is different. Blue light is more strongly diffracted.
The scattering of blue light is stronger than red light.
7. What is true for an IR detector used in astronomy?
Light is absorbed and the temperature increase is measured. Therefore, it is good to cool them.
They are based on the photoelectric effect: light kicks out electrons from the material.
The electrons in the detector need to get some additional energy to be used for detection. Thus, these detectors need to be heated.
They are not used. The IR part of the spectrum does not contain any information.
8. What is the reason why X-ray telescopes are so much different from telescopes for the visible part of the spectrum?
Materials used in these telescopes change the colour of the light. It is complicated to compensate this effect.
Materials are nearly transparent in the X-ray band. Standard optical configurations cannot be used.
It is hard to find materials that can be used under X-ray irradiation.
It is too dangerous to observe X-rays from astronomical objects.
9. What can be observed with radio astronomy?
Radio broadcast of other civilizations in the universe.
Wavelengths that are shorter than the visible light.
The moon.
Wavelengths that are in the region of cm.
10. Gravitational wave astronomy is called a new window to the universe. Why?
Gravitational waves have only a weak interaction with matter. They are carrying information from objects that cannot be observed by studying their emitted electromagnetic radiation.
Gravitational waves can be observed with a simple refractive telescope. Therefore, it would be easier to observe astronomical objects.
Gravitational waves will allow a very high resolution when combining a gravitational wave telescope with a CCD.
They need to be observed from space.
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