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6.2.1Space Physics

The Sun AS A Star — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 8 parts Lesson 14 of 24 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

6.2.1 The Sun as a Star — IGCSE Physics Notes — IGCSE PHYSICS notes: Describe the Sun as a medium-sized star made mainly of hydrogen and helium that is powered by nuclear fusion.Type — a medium-sized star at the centre of the Solar System.Composition — mostly hydrogen and helium.…

  • Main energy source
  • Origin of resources
  • Power source
  • Example reaction
  • Conditions
  • Thermal pressure

Part 1 of 6The Sun

The Sun
Type
  • Type a medium-sized star at the centre of the Solar System.
Composition
  • Composition mostly hydrogen and helium.
Age
  • Age about 4.6 billion years old.

Part 2 of 6Radiation from the Sun

Regions
  • Regions the Sun radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum.
Travel
  • Travel the energy reaches the Earth as electromagnetic radiation at 3.0 × 108 m/s through the vacuum of space.
Time
  • Time it takes about 8 minutes to reach the Earth.
RegionShare of energyEffect
InfraredAbout 50%Heating
VisibleAbout 40%Light and photosynthesis
UltravioletAbout 10%Can damage skin; the ozone layer absorbs some

Part 3 of 6Importance to the Earth

Main energy source
  • Main energy source it drives the weather, the water cycle and photosynthesis.
Origin of resources
  • Origin of resources fossil fuels, wind, waves and biomass all come from solar energy.

Part 4 of 6Nuclear fusion in stars (Extended)

Power source
  • Power source stable stars are powered by nuclear fusion in their cores.
Fusion
  • Fusion hydrogen nuclei join to form helium nuclei, releasing a huge amount of energy.
Example reaction
  • Example reaction hydrogen-2 + hydrogen-3 → helium-4 + a neutron.
  • Both are isotopes of hydrogen, formed by other fusion reactions in the star.
Conditions
  • Conditions a very high temperature and pressure are needed so that nuclei overcome their electrostatic repulsion.
Transfer
  • Transfer the energy released moves outwards and is radiated from the surface.

Part 5 of 6Stable star

Gravity
  • Gravity acts inwards and pulls the outer layers towards the core.
Thermal pressure
  • Thermal pressure acts outwards from the hot expanding gas as fusion releases energy.
Equilibrium
  • Equilibrium in a stable star the two forces are balanced.

Part 6 of 6More from the specification

1
Solar spectroscopic analysis
  • Solar spectroscopic analysis examining stellar absorption lines provides an astrophysical means to determine the Sun's elemental composition.
2
Galaxy
  • Galaxy a huge collection of stars, gas and dust held together by gravity, and the Sun is in the Milky Way
3
Redshift
  • Redshift light from distant galaxies has a longer observed wavelength because they are moving away from us
4
Hubble's law
  • Hubble's law the more distant a galaxy, the faster it recedes, which supports an expanding universe
5
Big Bang
  • Big Bang the universe began from a very small hot dense state about 13.8 billion years ago and has expanded since, shown by redshift and cosmic microwave background radiation
6
Galaxy
  • Galaxy a huge collection of stars, gas and dust held together by gravity, and the Sun is in the Milky Way
7
Redshift
  • Redshift light from distant galaxies has a longer observed wavelength because they are moving away from us
8
Hubble's law
  • Hubble's law the more distant a galaxy, the faster it recedes, which supports an expanding universe
9
Big Bang
  • Big Bang the universe began from a very small hot dense state about 13.8 billion years ago and has expanded since, shown by redshift and cosmic microwave background radiation
10
Light-year
  • The distance light travels in one year, 9.5 × 10¹⁵ m.
11
Galactic redshift
  • Shift of galaxy spectral lines to longer wavelength due to recession.
12
White dwarf
  • Small, hot, dense core left by a low-mass star.
13
Background radiation
  • Radiation that is always present in the environment.
14
Planetary nebula
  • The shell of gas ejected by a red giant.
15
Universe
  • All of space and everything in it.
16
Galaxy
  • Huge group of stars, gas, dust and solar systems held by gravity.
17
Redshift
  • Increase in the wavelength of light from a source moving away from the observer.
18
Distance
  • Total length of path travelled, a scalar.
19
Wavelength
  • Distance between a point on one wave and the same point on the next wave
20
Nebula
  • Cloud of gas and dust in which stars form.
21
Constant
  • Not changing.
22
v = H0d
What the symbols mean: v = recession speed of the galaxy (km s−1) · H0 = Hubble constant (km s−1 Mpc−1) · d = distance (Mpc)

Key terms

TermMeaning
StarA huge ball of hot gas that releases energy by nuclear fusion.
Nuclear fusionLight nuclei join to form a heavier nucleus, releasing energy.
Stable starA star in which inward gravity is balanced by outward thermal pressure.
InfraredRadiation that carries about half of the Sun's output and heats surfaces.
UltravioletRadiation of shorter wavelength than visible light that can damage skin.

Avoid these mistakes

1
The Sun burns fuel like a fire — it releases energy by nuclear fusion.
2
Fusion joins helium nuclei into hydrogen — hydrogen nuclei fuse into helium.
3
The Sun gives mostly X-rays — most energy is infrared, visible and ultraviolet.
4
Forgetting the balance in a stable star — gravity pulls inwards and thermal pressure pushes outwards.

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