Question:medium
Why is the mass of a nucleus always less than the sum of the masses of its
constituents, i.e. free neutrons and free protons?
Why is the mass of a nucleus always less than the sum of the masses of its
constituents, i.e. free neutrons and free protons?
Updated On: Jan 13, 2026
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Solution and Explanation
A nucleus's mass is consistently lower than the combined mass of its free constituent particles (like protons and neutrons). This discrepancy, termed mass defect, arises because a portion of the nucleons' mass is transformed into energy when they bind together to form the nucleus. This released energy, known as the binding energy, directly correlates to the mass loss, as described by Einstein's equation E = mc². Consequently, the mass of a nucleus is invariably less than the sum of the masses of its individual, unbound nucleons.
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