WJEC GCSE Physics
WJEC GCSE Physics 2.6 The Universe Exam Questions
Free WJEC GCSE Physics revision for 2.6 The Universe: what you need to know, common mistakes and exam-style questions with answers. Covers absorption spectra, red shift, Hubble's observations, the expanding Universe, the Big Bang and cosmic microwave background radiation.
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About WJEC GCSE Physics 2.6 The Universe
The Universe is the second space topic in Unit 2 and covers the evidence for how the Universe began. You need to explain how absorption spectra let astronomers identify the gases in stars, and how the shift of these lines towards the red end of the spectrum shows that galaxies are moving away from us. You must link Hubble's observations that more distant galaxies have greater red shift to the expansion of the Universe and the Big Bang model. Cosmic microwave background radiation is the second key piece of evidence. Examiners commonly ask you to interpret spectra diagrams and to explain how the evidence supports the Big Bang.
What you need to know
- Absorption spectra When white light passes through a cool gas, specific wavelengths are absorbed, producing dark lines in the spectrum. Each element has its own unique pattern, so the gases in a star's outer layers can be identified.
- Red shift Light from distant galaxies has its absorption lines shifted towards longer wavelengths (the red end). This shows the galaxies are moving away from us.
- Hubble's observations Hubble found that more distant galaxies have a greater red shift, so they are moving away faster. This shows the Universe is expanding.
- Big Bang model If the Universe is expanding, it must once have been much smaller, hotter and denser. The Big Bang model says the Universe began from a single, extremely hot and dense point and has expanded since.
- Cosmic microwave background CMB radiation comes from all directions in space. It is the remains of radiation from the hot early Universe, stretched to microwave wavelengths as the Universe expanded, and supports a hot Big Bang.
- Using evidence Red shift shows expansion and the CMB shows the Universe was once very hot and dense. Together they support the Big Bang model.
Common mistakes in 2.6 The Universe
- Saying red shift means galaxies are red. It means the spectral lines are shifted towards longer wavelengths.
- Describing the Big Bang as an explosion from a point in space. It was the expansion of space itself from an extremely hot, dense state.
- Stating that only red shift supports the Big Bang. Cosmic microwave background radiation is also key evidence.
- Saying more distant galaxies are moving slower. Hubble found that more distant galaxies show greater red shift, so they are moving away faster.
Try three 2.6 The Universe exam-style questions
1. Explain how astronomers can tell which elements are in the outer layers of a star. (3 marks)
Show the mark scheme answer
Light passes through gases in the star's outer layers; certain wavelengths are absorbed giving dark lines; the pattern matches the absorption spectrum of a particular element.
2. Spectra from galaxies A and B show the same lines, but B's lines are shifted further towards the red. What does this tell you about galaxy B compared with galaxy A? (2 marks)
Show the mark scheme answer
Galaxy B is moving away faster; so it is further away.
3. Describe two pieces of evidence for the Big Bang model. (4 marks)
Show the mark scheme answer
Red shift of light from distant galaxies; shows galaxies moving away / Universe expanding; cosmic microwave background radiation detected from all directions; remnant of radiation from hot early Universe.
2.6 The Universe FAQs
What does WJEC GCSE Physics 2.6 The Universe cover?
It covers absorption spectra, identifying gases in stars, red shift, Hubble's observations, the expansion of the Universe, the Big Bang model and cosmic microwave background radiation.
Which unit is The Universe examined in?
It is examined in Unit 2: Forces, Space and Radioactivity, a 1 hour 45 minute written paper worth 45% of the GCSE, sat at foundation or higher tier. The Unit 3 practical assessment draws on the same practical skills.
How do I answer red shift questions?
Compare the positions of the dark lines with a reference spectrum, state which way they have moved, then link a larger shift to greater speed and greater distance. Finish by linking it to an expanding Universe.
