EL1 Flashcards
what are fusion reactions?
when lighter nuclei join to give heavier nuclei, this is how certain elements are formed.
where is nuclear fusion common?
in the centre of stars
how does nuclear fusion occur?
both nuclei approach each other at high speed, with a large kinetic energy to overcome repulsion.
what conditions does nuclear fusion require?
extreme temperature and gravitational pressure.
how could nuclear fusion be useful within modern society?
the vast amount of energy produced with no pollution could be useful as a source of energy if conditions could be controlled.
what does the theory of the evolution of stars show?
how heavy elements can be formed from lighter ones.
what does the the theory of the evolution of stars explain?
the way elements are distributed throughout the universe.
what feature of heavyweight stars allows fusion reactions to occur?
the extreme temperature and gravitational pressure.
what happens when fusion reactions occur within heavyweight stars?
layers of elements form; the heaviest forms at the centre.
what element eventually forms at the centre of heavyweight stars?
iron.
what happens when the core of a heavyweight star becomes mostly iron?
it becomes unstable and explodes.
why do heavyweight stars explode when their core is mostly iron?
when iron nuclei fuse together, they do not release energy but absorb it.
what happens once a heavyweight star has exploded?
a supernova causes the elements in the star to be dispersed in the universe as clouds of dust and gas; the life cycle then repeats.
what is an example of a lightweight star?
the sun.
what are the differences between heavyweight and lightweight stars?
lightweight stars are not as hot and will last longer; they will keep shining until all hydrogen is used up and there will be no supernova.
