Download OCR Physics A Refer to the Physics A datasheet for data, formulae

OCR Physics A
20 Cosmology (The Big Bang)
Exam-style questions
Refer to the Physics A datasheet for data, formulae and relationships information.
1
a
Explain what is meant by:
i
light year
(1 mark)
ii
parsec.
(1 mark)
b Acrux is the brightest star in the Southern Cross. When viewed through a
telescope it is seen to consist of two component stars with a separation of
4.0 arc seconds. Given that Acrux is 320 ly from Earth determine the distance
between the two component stars. Give your answer in metres.
(3 marks)
c
The Whirlpool galaxy is 23 million light years from the Earth. Calculate the
distance to this galaxy in parsecs.
(2 marks)
2
The red shift of a galaxy’s spectrum can be used to determine the velocity of the
galaxy relative to Earth.
a
The wavelength of the hydrogen alpha line in the spectrum of a galaxy is
measured to be 660.92 nm. The wavelength of the same line measured in the
laboratory is 656.28 nm. Calculate the velocity of the galaxy.
(2 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
1
OCR Physics A
20 Cosmology (The Big Bang)
Exam-style questions
b The table below gives the velocity and distance of five galaxies observed in
different constellations.
Galaxy in
constellation of
Velocity/km s1
Distance/Mpc
Virgo
1 200
15
Ursa Major
15 400
190
Corona Borealis
22 000
280
Bootes
39 400
490
Hydra
60 600
760
Plot a graph of the data in the table and use it to determine a value for the
Hubble constant.
(4 marks)
3
a
Observations on a binary star system show that each of the stars are rotating
about their common centre of mass with an orbital speed of 390 km s1.
A prominent absorption line due to hydrogen is observed in the spectrum
from the binary system. The wavelength of this line measured from a
laboratory source is 656.28 nm.
Calculate the maximum and minimum values for the wavelength of this line
due to the stars’ orbital motion.
(3 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
2
OCR Physics A
20 Cosmology (The Big Bang)
Exam-style questions
b The Andromeda galaxy is currently located at a distance of 725 kpc. It is
known to be approaching the Milky Way at a speed of 105 km s1.
i Atomic hydrogen emits a strong radio signal at a wavelength of
0.211207 m as measured in the laboratory. The same radio signal is
detected in emissions from the Andromeda galaxy. Explain why the
wavelength of this signal is different from the value observed in the
laboratory.
Calculate the wavelength of the signal in Andromeda’s spectrum.
You should work to 6 d.p. in this calculation.
(4 marks)
ii
It is thought that the Andromeda galaxy may eventually collide with the
Milky Way. Estimate the time, in s, which will elapse before a possible
impact with the Milky Way.
(2 marks)
iii
State one assumption you have made in determining your answer to ii.
(1 mark)
4
a
Explain how astronomers are able to deduce that most galaxies are moving
away from Earth.
(3 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
3
OCR Physics A
20 Cosmology (The Big Bang)
Exam-style questions
b Figure 1 shows a graph of recessional speed of some galaxies plotted
against their distance from Earth.
Figure 1
Sketch a best fit straight line on Figure 1 and hence determine a value for the
Hubble constant.
(2 marks)
c
The presence of calcium in a galaxy is indicated by a strong absorption line
in the spectrum. In the laboratory this line occurs at 390.0 nm. The same line
is observed to occur at 395.7 nm in the spectrum from a particular galaxy.
i Calculate the recessional speed of the galaxy.
(3 marks)
ii
Use Figure 1 to estimate the distance of the galaxy from Earth.
(1 mark)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
4
OCR Physics A
5
20 Cosmology (The Big Bang)
Exam-style questions
The graph shows the spectrum of the cosmic microwave background radiation.
The shape of the graph is consistent with a black-body spectrum to which the
Wien displacement law may be applied.
Figure 2
a
Use the graph to estimate the black-body temperature.
Wien constant 2.9 × 103 m K
(2 marks)
b Explain how your answer to a provides evidence in support of the Big Bang
theory for the origin of the Universe.
(2 marks)
c
State and explain another piece of experimental evidence in support of the
Big Bang theory.
(2 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
5
OCR Physics A
6
20 Cosmology (The Big Bang)
Exam-style questions
A binary star system consists of two stars, A and B, rotating about their common
centre of mass. Figure 3 shows three absorption lines in the spectra from the
binary system measured over a period of time. The diagram is not drawn to
scale.
Figure 3
a
Use Figure 4 to describe the motion of the system and explain why the
observed absorption lines change with time in the way illustrated in Figure 3.
Figure 4
(5 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
6
OCR Physics A
20 Cosmology (The Big Bang)
Exam-style questions
b What is the period of this binary system?
(1 mark)
c
Using the wavelength values given in the Figure 3, calculate the observed
speed of star A, relative to star B.
(2 marks)
© Oxford University Press 2016 http://www.oxfordsecondary.co.uk/acknowledgements
This resource sheet may have been changed from the original
7