physics: nuclear fusion

conditions necessary for nuclear fusion to start.(2)

extremely high pressure

extremely high temperature

Describe what happens in this nuclear fusion reaction.(2)

hydrogen nuclei fuse to form helium nuclei

to become a main sequence star

Describe how the orbit of a comet compares with the orbit of a planet.(3)

comet has an eliptical orbit but a planet has a circular one.

path of comet is longer

speed of comet varies but speed of planet does not

Suggest why planets have different gravitational field strengths at their surface.(1)

different mass and densities

describe the evolution of the Sun from the start of its life to the end of its life.(4)

begins as a nebula

gravity starts pulling forming a protostar

when the protostar begins to emit light it is a star

When hydrogen runs out

it expands into a red giant

then collapses to a white dwarf

Discuss the difference between a red giant star and a white dwarf star.(4)

red giant has greater brightness than white dwarf

nuclear fusion takes place in red giant giant not white dwarf

red giant has lower temp than white dwarf

white dwarf is denser than a red giant