# GCSE level questions on the Earth in Space

Q3.

The energy radiated by a main sequence star like the Sun is released by a nuclear fusion reaction in its core.

• The net result of the nuclear fusion reaction is that four hydrogen nuclei produce one helium nucleus. There is a loss of mass of 0.7%.
• For nuclear fusion to occur nuclei must collide at very high speeds.
• The energy released during the reaction can be calculated as shown:

Energy released [J] = loss of mass [kg] x (speed of light [m/s2])2

(The speed of light is 3.0 x 108 m/s)

(a) Calculate the energy released when 1g of hydrogen fuses to form helium. (Show your working.) (4 marks)

(b) The table below shows the lifetimes and surface temperatures of main sequence stars with different masses.

 Mass of Star [SUN = 1] Lifetime on main sequence [Millions of years] Surface Temperature* [Kelvin] 0.5 200 000 4000 1 10 000 6000 3 500 11 000 15 15 30 000

[* The higher the surface temperature of a star, the higher the temperature and pressure in its core.]

Describe the relationship between the lifetime of a main sequence star and its mass. (1 mark)

(Total 5 marks)