Scientists think that the cosmic microwave background radiation (CMBR) was emitted as high-energy radiation soon after the Big Bang.
Why is this radiation detected as microwaves today?
The expansion of the universe has stretched its wavelength
Dust in space has absorbed it and emitted microwaves instead
It has slowed down as it travelled through space to the Earth
Its frequency has increased as the universe has cooled down
50 exam-style questions on OCR GCSE Physics 8.3 Beyond Earth, covering 8.3.1 Red-shift and the expanding universe, 8.3.2 Evidence for the Big Bang model, 8.3.3 Formation of the Sun and stellar equilibrium, 8.3.4 Radiation emitted by hot bodies, 8.3.5 The solar system and satellites, 8.3.6 Gravity and circular orbits, 8.3.7 Orbital radius and orbital speed, 8.3.8 Radiation balance and the temperature of the Earth, and 8.3.9 Seismic waves and exploring hidden structures. Each one has a worked solution and a mark scheme showing where the marks go.