Fusion and Stars · Paper 1 — Free Physics SL Practice Questions

A binding energy per nucleon graph shows that hydrogen-1 has a binding energy per nucleon of approximately $0\ \text{MeV}$ and helium-4 has a binding energy per nucleon of approximately $7.1\ \text{MeV}$. When four hydrogen nuclei fuse to form one helium-4 nucleus, which statement correctly explains why energy is released?

A star spends several billion years on the main sequence before its luminosity increases by a factor of approximately $10^3$. Which evolutionary stage is responsible for this sharp luminosity increase?