Fusion — Science definition
The joining of light nuclei into heavier nuclei, with energy release in appropriate reactions.
Where it is taught
- Stars, Fusion & Element Formation — Stars & the Universe, Earth & Space Science, Grade 9
In use
A star forms when a cloud contracts under gravity and its interior becomes hot and dense enough for sustained nuclear fusion.
Stars, Fusion & Element Formation
Questions using fusion
Problem 1
What distinguishes fusion from chemical burning in a star? Show the reasoning, not just the conclusion.
Hints
Compare supply with consumption rate.
Answer and explanation
Fusion changes nuclei and releases nuclear energy; ordinary chemical reactions rearrange electrons and atoms without that nuclear transformation.
Problem 2
Describe the chain connecting fusion in the Sun to warming at Earth’s surface.
Answer and explanation
Fusion releases energy, energy moves through the solar interior, radiation leaves the surface and crosses space, and absorption transfers energy to Earth.
Problem 3
In a main-sequence star, fusion mainly converts
- hydrogen into helium
- helium into hydrogen
- iron into gold
- carbon into oxygen
Answer and explanation
hydrogen into helium
Hydrogen fusion powers stars for most of their lives.