The source of the Sun's energy is
- A.Fusion of heavy nuclei
- B.Fusion of lighter nuclei
- C.Fission of light nuclei
- D.Fission of heavy nuclei
Correct answer
Explanation
The correct answer is B, fusion of lighter nuclei. In the core of the Sun, at a temperature of about fifteen million kelvin, four hydrogen nuclei combine through the proton-proton chain to form one helium nucleus. The mass of the helium nucleus is slightly less than the mass of the four hydrogen nuclei, and this difference appears as energy according to the mass-energy relation, which is why the Sun has been able to shine for billions of years. Option A is wrong because heavy nuclei do not fuse easily; fusion releases energy only for light nuclei, up to about iron. Option C and option D both name fission, the splitting of a nucleus, which is the reaction used in nuclear power stations and in the atom bomb; fission of heavy nuclei such as uranium releases energy, but it is not what happens in a star. Remember the rule: stars fuse light nuclei, reactors split heavy ones.
Read the full article: Space Science: Stars, Galaxies and Satellites Notes
Practice Questions
View allWhat is the reason behind the twinkling of stars?
- A.Scattering of light by dust particles
- B.Internal reflection of light by clouds
- C.Atmospheric refraction of star light
- D.Dispersion of light by water droplets
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A star is so far away that it is a point source of light.
Read the full explanation →Once a satellite has been launched into orbit, the only force governing its motion is the force of ______.
- A.gravity
- B.elasticity
- C.friction
- D.fuel driven
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A satellite is given the required height and speed by its launch vehicle, and after that no engine is needed: the gravitational pull of the earth alone acts on it and provides the centripetal force that keeps it in a curved path, so the satellite keeps falling towards the earth…
Read the full explanation →A light year is a unit of
- A.Time
- B.Distance
- C.Brightness
- D.Mass
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A light year is the distance travelled by light in vacuum in one year, which is about 9.46 times ten to the power twelve kilometres, or roughly nine and a half trillion kilometres.
Read the full explanation →Which is the nearest star to the earth after the Sun?
- A.Sirius
- B.Proxima Centauri
- C.Polaris
- D.Betelgeuse
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Being a red dwarf it cannot be seen with the naked eye, although it is the closest star to us after the Sun.
Read the full explanation →A geostationary satellite completes one revolution around the earth in
- A.90 minutes
- B.12 hours
- C.24 hours
- D.365 days
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A geostationary satellite is placed in a circular orbit about 35,786 kilometres above the equator, where its period of revolution equals the period of rotation of the earth about its axis, and it moves from west to east like the earth, so it appears to stay over the same point…
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