AQA A-Level Physics Exam Questions: Astrophysics, Cosmology, & Practical Skills

,Q1.

(a) The table summarises some of the properties of two stars in the constellation of Ursa Minor.



spectral
apparent radius of star radius
name
magnitude of the Sun
class

Polaris 2.0 50 F

Kocab 2.0 50 K

(i) Using these data, describe and explain one similarity and one difference in the
appearance of the two stars as seen with the unaided eye by an observer on the Earth.

similarity_______________________________________________________

______________________________________________________________
______________________________________________________________
difference______________________________________________________

______________________________________________________________

______________________________________________________________

(2) (ii) Deduce which of the two stars is further from the Earth.

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

______________________________________________________________

(3)

(b) Ursa Minor also contains the galaxy NGC 6251. Measurements indicate that the light from the
galaxy has a red shift, z, of 0.025 and that the galaxy is 340 million light years from Earth.

(i) Use these data to calculate a value for the Hubble constant.




value ____________________ k ms–1 Mpc–1

(3)

, (ii) Use your answer to part (b)(i) to estimate a value for the age of the Universe. State an
appropriate unit for your answer.




age ____________________ unit __________

(3)

(Total 11 marks)

Q2.

(a) Bellatrix and Betelgeuse are stars in the constellation of Orion. Some of their properties are
summarised below.



Bellatrix Betelgeuse

absolute magnitude –6.0 –2.7

apparent magnitude 0.4 1.6

black-body temperature / K 22 000 2 400

(i) Explain what is meant by absolute magnitude.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(1) (ii) Which of the two stars is closer to the Earth? Explain your answer.

______________________________________________________________

______________________________________________________________

______________________________________________________________

(1)

(b) (i) Calculate the wavelength of the peak intensity in the black-body radiation curve of
Bellatrix.

, answer = ____________________ m

(2)

(ii) Sketch the black-body radiation curve for Bellatrix. Label the wavelength axis with a suitable scale.




(3)

(c) Detailed analysis of the light from both stars reveals the presence of prominent absorption lines in
the spectra.

(i) To which spectral class does Bellatrix belong?

______________________________________________________________

(1)

(ii) Prominent features in the Bellatrix spectrum are the Balmer absorption lines due to
hydrogen. State the other element responsible for the prominent absorption lines in the
spectrum of Bellatrix.

______________________________________________________________

(1)

(iii) Why does the spectrum of Betelgeuse not contain prominent Hydrogen Balmer

absorption lines?