COSMOLOGY

Light from a distant galaxy is analysed. The line spectrum obtained is compared with similar radiation from the Sun.

When compared with the light from the Sun, a line in the spectrum of light from the distant galaxy has a

• higher frequency and a greater photon energy.

• higher frequency and a smaller photon energy.

• lower frequency and a greater photon energy.

• lower frequency and a smaller photon energy.

The gravitational field strength on the surface of Mars is g. The Moon has about the same density as Mars but only half the radius.

What is the gravitational field strength on the surface of the Moon?

• g/4

• g/2

• 2g

• 4g

Cosmologists predict a number of alternatives for the future evolution of the universe.

Which of the following statements describes an open universe?

• The density of the universe equals the critical density.

• The universe eventually reaches a maximum size

• The universe will keep on expanding forever

• We cannot predict the eventual fate of the universe

Quasars are thought to be discs of matter moving around black holes. Light received from all quasars shows large red shifts.

Which of the following can be concluded from this?

• Quasars are accelerating away from the Earth at a large rate.

• Quasars are accelerating towards the Earth at a large rate.

• Quasars are moving away from the Earth very quickly.

• Quasars are moving towards the Earth very quickly.

A star is moving towards the Earth with a velocity of 1.2 × 10⁶ m s⁻¹.
Light of wavelength 780 nm is emitted from the star.

What would be the wavelength of the light, in nm, recorded by an observer on the Earth?

• 195 nm

• 783 nm

• 777 nm

• 975 nm

Recent measurements indicate that the value of the Hubble constant is greater than previously estimated.

Which of the following statements could be a consequence of this?

• The universe might be bigger than we thought.

• The universe might not be as big as we thought.

• The universe might be older than we thought.

• The universe might not be as old as we thought.

Dark matter is known to exist because it

• emits high energy X-rays.

• exerts gravitational forces on matter.

• is predicted by the Standard Model.

• obscures distant galaxies.

Two stars are being observed. Star X is twice as far away as star Y and the radiation flux received from star X is half that from star Y.

Which of the following statements is correct?

• Star X has half the luminosity of star Y.

• Star X has the same luminosity as star Y.

• Star X has twice the luminosity of star Y.

• Star X has eight times the luminosity of star Y.

Star X has a luminosity L and is a distance x from the Earth. The radiation flux received
from this star is F.

Star Y has a luminosity 3L and is a distance 2x from the Earth.

What is the radiation flux received from star Y?

• 3F/4

• 2F/3

• 4F/3

• 3F/2

The Sun has a radius R, surface temperature T and luminosity L.

A white dwarf has a surface temperature 5T and luminosity L/16

Which of the following is the radius of the white dwarf in terms of R?

• R/5

• R/25

• R/100

• R/10000