The semi-empirical mass formula named for Bethe and Weizsäcker is used to calculate nuclear binding energy using its namesake defect. What quantity is this formula associated with?

• A. Charge
• B. Momentum
• C. Energy
• D. Mass

Answer: (D)

The essential idea is binding energy. The Bethe–Weizsäcker semi-empirical mass formula estimates how much energy is needed to disassemble a nucleus into separate protons and neutrons. That energy comes from the mass defect—the difference between the mass of the nucleus and the sum of the masses of its constituent nucleons—converted to energy via E = mc^2. So the formula is tied to energy (binding energy) because it quantifies the energy associated with the nuclear binding. If you ever need the corresponding mass difference, you can convert the energy back to mass with E/c^2, but the formula itself directly gives energy.