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)
mass into kg (mass = 0.001kg) 
0.7% of mass is converted to energy = 0.000 007kg
E = mc2 = 0.000 007 x (3.0 x 108)2
= 0.000 007 x 9.0 x 1016
= 6.3 x 1011 J
(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 |
Describe the relationship between the lifetime of a main sequence star and its mass. (1 mark)
The idea that the bigger the mass the shorter the life gains 1 mark but idea that decrease in life is much more than proportional to increase in mass is a better answer
(Total 5 marks)
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