Physics / Unit 10: Magnetism and Modern Physics
10.7 Nuclear Energy
Notes
Nuclear reactions release huge amounts of energy because a little mass is converted to energy: $E = mc^2$.
- Fission: a heavy nucleus (like uranium-235) splits into smaller nuclei after absorbing a neutron, releasing energy and more neutrons that can start a chain reaction. Nuclear power plants use controlled fission.
- Fusion: light nuclei (like hydrogen) join to form a heavier nucleus (like helium). Fusion powers the Sun and needs extremely high temperature and pressure.
- Nuclear power produces no carbon dioxide while running but creates radioactive waste.
- Example: converting $0.001 \text{ kg}$ of mass to energy releases $E = 0.001 \times (3.0 \times 10^8)^2 = 9.0 \times 10^{13} \text{ J}$.
Practice
What process releases the energy in the Sun?
In the Sun's hot core, hydrogen nuclei fuse.
How much energy is released if $2.0 \times 10^{-3} \text{ kg}$ of mass is converted completely to energy?
$E = mc^2 = (2.0 \times 10^{-3})(9.0 \times 10^{16}) = 1.8 \times 10^{14} \text{ J}$.
In a fission chain reaction, what keeps the reaction going?
Each fission releases extra neutrons that can cause more fissions.
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