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8.3.2The Periodic Table

Red-Shift — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 17 of 23 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 4What Red-Shift Is

Red-shift
  • Red-shift An observed increase in the wavelength of light from distant galaxies, moving it towards the red end of the spectrum.
Absorption lines
  • Absorption lines Dark lines in a distant galaxy's spectrum appear at longer wavelengths than the same lines from a nearby source such as the Sun.
Blue-shift
  • Blue-shift Light from a source moving towards the observer is shifted to shorter wavelengths, towards the blue end.
Distance link
  • Distance link Galaxies that are further away show a greater red-shift, which means they are moving away faster.

Part 2 of 4Evidence for Expansion

1
Light from most distant galaxies is red-shifted, which means those galaxies are moving away from Earth.
2
The further a galaxy is from Earth, the greater its red-shift, and so the faster it is moving away.
3
If all distant galaxies are moving away from one another, the space between them must be expanding.
4
Running this expansion backwards shows that the Universe was once much smaller, which supports the Big Bang model.

Part 3 of 4Interpreting Red-Shift

Interpreting Red-Shift
Stretching
  • Stretching The wavelength is stretched because space itself is expanding, not only because galaxies move through space.
Hubble graph
  • Hubble graph A graph of speed against distance shows that more distant galaxies are moving away faster.
Balloon model
  • Balloon model Points on an inflating balloon move apart as it expands, similar to galaxies in an expanding Universe.
Evidence
  • Evidence The red-shift of distant galaxies is strong evidence that the Universe is expanding.

Part 4 of 4Exam Checklist & Tips

8.3.2 – Key Points for the Exam

  • Red-shift An increase in the observed wavelength of light from a receding source.
  • Absorption spectrum A spectrum with dark lines at wavelengths where particular elements absorb light.
  • Blue-shift A decrease in the observed wavelength of light from an approaching source.
  • Expanding Universe The idea that space itself is growing, so galaxies move apart.
  • Hubble law The relationship that more distant galaxies are receding at greater speeds.

Common Mistakes

  • Saying that galaxies look red because they are red; red-shift is a change in the wavelength of their light.
  • Stating that a greater red-shift means a galaxy is closer;
    • a greater red-shift means a larger distance and speed.
  • Thinking that red-shift is caused only by the stars moving;
    • the stretching of wavelength is caused by the expansion of space.

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Cambridge 9702 & Edexcel Physics Mark Scheme Points

Doppler Shift & Galactic Red-shift Criteria

Key Equation: Δλ / λ ≈ Δf / f ≈ v / c

  • Red-shift: Fractional increase in observed wavelength from receding galaxies.
  • Hubble's Law: v = H0d (Universe age ≈ 1 / H0).
  • Evidence for Big Bang: Cosmological red-shift + CMBR at 2.7K.
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