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Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, with some mass converted into energy of radiation. Free GCSE Physics notes.
Introduction to Nuclear Fusion is part of Nuclear fission and fusion (physics only) in GCSE AQA Higher Physics.
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Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, with some mass converted into energy of radiation. Free GCSE Physics notes.
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Use this lesson to stay inside Nuclear fission and fusion (physics only) while connecting the detail back to the wider Atomic structure topic.
Read the core explanations from Introduction to Nuclear Fusion before testing yourself from memory.
Picture the Sun burning above you right now. That incredible energy powering all life on Earth comes from nuclear fusion - the most powerful energy source in the universe. But what exactly happens inside those stellar furnaces?
Think of fusion like this: imagine trying to push two powerful magnets together - they repel each other with enormous force. Nuclei behave similarly because they're both positively charged. But if you can force them close enough together, something amazing happens - they suddenly snap together and release tremendous energy.
The key word here is 'light' nuclei. Fusion works best with the smallest atoms - hydrogen, helium, and lithium. These have fewer protons, so the repulsive forces are weaker and easier to overcome.
The most common fusion reaction happens in stars like our Sun. Two hydrogen nuclei (each containing just one proton) smash together at incredible speeds. When they fuse, they create a heavier nucleus - helium.
But here's where it gets interesting: the helium nucleus has slightly less mass than the two hydrogen nuclei that created it. Where did that 'missing' mass go? It didn't disappear - it converted into pure energy.
This process requires extreme conditions. The nuclei need to be moving fast enough to overcome their mutual repulsion - that means temperatures of millions of degrees Celsius. At these temperatures, matter exists as plasma, where electrons are stripped away from atoms.
Fusion releases energy when some mass is converted into energy of radiation.
**Trap**: In fusion, only some of the mass is converted into energy of radiation. The rest forms the new, heavier nucleus.
Worked example: Fusion energy release
Explain how fusion can release energy. [3 marks]
Answer: Fusion releases energy as radiation.
Students often confuse fusion with fission - they're opposite processes. Fusion joins light nuclei together; fission splits heavy nuclei apart. Both release energy, but through completely different mechanisms.
| Feature | Nuclear Fusion | Nuclear Fission |
|---|---|---|
| Process | Light nuclei join together | Heavy nucleus splits apart |
| Starting materials | Hydrogen, helium, lithium | Uranium, plutonium |
| Conditions needed | Extreme heat (millions °C) | Can occur at room temperature |
| Products | Heavier nucleus + energy | Lighter nuclei + neutrons + energy |
| Control | Very difficult to sustain | Can be controlled with rods |
The energy per kilogram from fusion is much higher than fission. This is why stars use fusion - it's the most efficient way to convert matter into energy in the universe.
Fusion joins light nuclei to form a heavier nucleus, and some mass may be converted into energy of radiation.
The challenge is recreating stellar conditions on Earth. We need to heat hydrogen to 100 million°C and keep it contained long enough for fusion to occur. At these temperatures, no material container can hold the plasma - it would instantly vaporise.
Scientists use powerful magnetic fields to contain the plasma, creating a 'magnetic bottle'. Current fusion reactors can achieve fusion, but they use more energy to run than they produce. The goal is 'ignition' - where the reactor produces more energy than it consumes.
Fusion questions test your understanding of nuclear processes and energy calculations. Examiners love to ask about the differences between fusion and fission, so make sure you can compare them clearly.
In questions about fusion, explain that fusion joins light nuclei to form a heavier nucleus and some mass may be converted into energy of radiation.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Nuclear fusion is the joining of two light nuclei to form a heavier nucleus, in which some of the mass may be converted into the energy of radiation. It powers stars like the Sun, where hydrogen nuclei fuse to form helium.
Fusion joins light nuclei together to form a heavier nucleus, while fission splits a heavy nucleus apart into lighter nuclei plus neutrons. Both release energy, but fusion needs extreme heat of millions of °C, while fission can occur at room temperature and can be controlled with rods.
Plasma is the state of matter at temperatures of millions of degrees Celsius, where electrons are stripped away from atoms. Fusion happens in plasma because the nuclei are moving fast enough to overcome their mutual repulsion.
Fusion energy comes from mass being converted into energy of radiation. The helium nucleus formed has slightly less mass than the hydrogen nuclei that created it; only some of the mass is converted, and the rest forms the new, heavier nucleus.
Fusion ignition is the goal of a fusion reactor producing more energy than it consumes. Current fusion reactors can achieve fusion, but they use more energy to run than they produce.
The challenges of fusion power are the extreme temperatures needed, the plasma being difficult to contain, and that current reactors use more energy than they produce. Fusion is very difficult to sustain.
Fusion needs temperatures of millions of degrees Celsius because nuclei are positively charged and repel each other. They must move fast enough to overcome this mutual repulsion and get close enough to fuse; at these temperatures matter exists as plasma.
Fusion is hard on Earth because hydrogen must be heated to 100 million°C and contained long enough for fusion to occur, and no material container can hold the plasma. Scientists use powerful magnetic fields as a 'magnetic bottle', but current reactors use more energy than they produce.
The Sun's energy comes from nuclear fusion. Two hydrogen nuclei smash together at incredible speeds and fuse to create a heavier helium nucleus, and the slightly lower mass of the helium is converted into energy.
Plasma in a fusion reactor is contained using powerful magnetic fields, creating a 'magnetic bottle'. No material container can hold plasma at 100 million°C because it would instantly vaporise.
Fusion power offers clean fuel, no carbon emissions, no meltdown risk and an abundant fuel supply. The energy per kilogram from fusion is also much higher than from fission.
Fusion works best with the smallest atoms: hydrogen, helium and lithium. These have fewer protons, so the repulsive forces between them are weaker and easier to overcome.
Only some of the mass is converted into energy of radiation in fusion; the rest forms the new, heavier nucleus. The helium nucleus has slightly less mass than the two hydrogen nuclei that made it.
Fusion releases much more energy per kilogram than fission. This is why stars use fusion, the most efficient way to convert matter into energy in the universe.
Nuclei repel each other because they are all positively charged, like two powerful magnets pushing apart. If they are forced close enough together at extreme temperatures, they snap together and release tremendous energy.