CBSE Class 12 · 2023 · Modern PhysicsShort Answer

Define the term mass defect. How is it related to the stability of the nucleus?

Answer: $Δ m = [Z m_{p} + (A - Z) m_{n}] - M$ ; larger $Δ m \Rightarrow$ more stable.

Solution

Mass defect

Δ m

is the difference between the sum of the masses of the free constituent nucleons and the actual mass of the nucleus:

Δ m = [Z m_{p} + (A - Z) m_{n}] - M_{nucleus} .

This missing mass appears as the binding energy

E_{b} = Δ m c^{2}

. A larger mass defect means a larger binding energy per nucleon and hence a more stable nucleus.

Δ m = [Z m_{p} + (A - Z) m_{n}] - M; larger Δ m \Rightarrow more stable

CBSE Class 12 Board · 2023 · Subjective