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Home · IGCSE 0625 · Space physics · CMBR and Hubble · Practice
Extended · Practice questions · CMBR and the Hubble constant
Supplement (Extended) content

Evidence and the constant.

Six original Cambridge-style questions on the cosmic microwave background, Hubble's law, and the age of the universe.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

Glow, law, age.

01
Recall
[2 marks]

State what the cosmic microwave background radiation is, and where it comes from in the sky.

  • Microwave radiation left over from the early universe. ✓
  • It comes from all directions in space. ✓
02
Recall
[1 mark]

State what the CMBR is evidence for.

  • The Big Bang theory. ✓
03
Recall
[2 marks]

Write down Hubble's law and state what each symbol represents.

  • v = H0 d. ✓
  • v is recession speed, d is distance, H0 is the Hubble constant. ✓
04
Calculation
[2 marks]

A galaxy is at a distance of 4.0 x 10 to the 24 m and recedes at 8.8 x 10 to the 6 m/s. Calculate the Hubble constant H0.

H0 = v / d = (8.8 x 10 to the 6) / (4.0 x 10 to the 24)

H0 = 2.2 x 10 to the minus 18 per second

05
Calculation
[2 marks]

Using H0 = 2.2 x 10 to the minus 18 per second, estimate the age of the universe in seconds.

age = 1 / H0 = 1 / (2.2 x 10 to the minus 18)

age = 4.5 x 10 to the 17 s (about 14 billion years)

06
Analysis
[2 marks]

Speeds and distances are measured for many galaxies and plotted as a graph of v against d. Explain how the Hubble constant is found from this graph.

  • The points lie on a straight line through the origin. ✓
  • The gradient (slope) of the line is the Hubble constant H0. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.