Mass-energy equivalence
The principle that mass and energy are interchangeable, expressed by Einstein's equation E = mc², where E is energy, m is mass, and c is the speed of light (3 × 10⁸ m/s). A small amount of mass corresponds to an enormous amount of energy (c² ≈ 9 × 10¹⁶ J/kg). This principle explains the energy released in nuclear reactions, where a tiny mass defect yields large energy.
Formula
E = mc²
Real World
The atomic bomb dropped on Hiroshima in 1945 converted less than 1 gram of uranium mass into energy — equivalent to roughly 15,000 tonnes of TNT — demonstrating the enormous scale of c².
Exam Focus
Convert mass defect to kg (×1.66×10⁻²⁷ for atomic mass units) before multiplying by c²; forgetting unit conversion is the most common error.
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