P2.6 Flashcards
What does nuclear fission produce?
Heat, which is used to generate electricity
What main substances are used in nuclear fission?
~ Uranium235
~ Plutonium239
How do nuclear power stations work?
~ Fuel rods of uranium235 or plutonium239 make heat ~ Heat warms the water ~ Produces steam ~ Turns turbines ~ Generates electricity
What happens when a neutron is fired into a nucleus?
~ The nucleus splits into 2 nuclei
~ 2 or 3 more neutrons are released
What is a chain reaction?
When neutrons produced from the splitting of a nuclei hit into more nuclei and the chain continues
How is nuclear fission controlled so it doesn’t continue forever?
Some substances can be used to absorb the neutrons
What is nuclear fusion?
When the nucleus of one atom joins with the nucleus of another atom
What is the problem with nuclear fusion?
Each nucleus has a positive charge so they strongly repel and it’s difficult to get them to fuse
Where does nuclear fusion happen?
In the centre of stars
What gases make up the sun?
75% hydrogen
25% helium
What makes nuclei fuse?
~ Heat
~ Gravitational force
When 2 hydrogen nuclei fuse what do they form?
Helium nucleus
Why should energy from nuclear fission be used in power stations?
~ Not radioactive
~ Better byproduct for the environment
What is one disadvantage of nuclear fusion?
High temperatures required
What is a disadvantage of nuclear fission?
Produces radioactive waste
What were the first two elements produced 100,000 years after the Big Bang?
Hydrogen and helium
What is a protostar?
A cloud of hydrogen and helium
What force acts as hydrogen and helium get closer together?
Gravity
What happens when gravity increases in a protostar?
The hydrogen fuse together
In a main sequence star the gravity is equal to what?
The force caused by nuclear radiation
What happens to a main sequence star after billions of years?
~ It runs out of hydrogen and the fusion reactions decrease
~ Star becomes a red giant
Why does a red giant star shrink to a white dwarf star?
Because it runs out of fuel
What happens to stars about the size of the sun at the end of their life?
~ It will expand and become a red giant
~ Red giant cools and collapses under its own gravity to become a white dwarf
~ White dwarf slowly cools to become a black dwarf
What happens to stars larger than the sun at the end of their life?
~ Expand to become red supergiants
~ Shrinks and explodes which releases lots of energy, dust and gas into space (supernova)
~ Remains may form a neutron star, some of these collapse to form black holes
What element is produced in the centre of stars?
Iron
What elements are produced from a supernova?
Elements heavier than iron
What is a black hole?
A very dense body which attracts everything and doesn’t let anything escape, even light
What is the solar system believed to have formed from?
Material produced when earlier stars exploded
What must happen before nuclear fission can happen?
The uranium235 or plutonium239 must absorb a neutron
How do stars form?
Dust and gas from space is pulled together by gravitational attraction
How do planets form?
From smaller masses being attracted by a larger mass
How have all of the naturally occurring elements been produced?
Through fusion processes in stars
