Key relationship
Δm=Z mH+N mn−M(atom); B=Δm c²; 1 u c²≈931.494 MeV.
Physics · Class 12
Mass defect and binding
A bound system has less mass than its separated constituents. The mass difference corresponds to the energy needed to separate the nucleus. Atomic and nuclear mass conventions must not be mixed.
Open the interactive experiment →Mass defect and binding
பிணைந்த அணுக்கருவின் நிறை தனித்த துகள்களின் மொத்த நிறையை விடக் குறைவு. நிறைக் குறைவு பிணைப்பு ஆற்றலுக்கு இணையாகும்.
Key notes, relationships and model limits
Remember
A bound system has less mass than its separated constituents. The mass difference corresponds to the energy needed to separate the nucleus. Atomic and nuclear mass conventions must not be mixed.
Common trap
Do not combine proton masses with atomic isotope masses without cancelling electron masses.
Model limits
Atomic-mass convention cancels Z electron masses using hydrogen-atom mass. Electron binding neglected. Inconsistent isotope/mass inputs can give negative binding and are flagged rather than absolutized.
What you will learn
Convert a mass difference into nuclear binding energy.
Try the experiment
Try both scenarios, change one control, and predict the result before checking the graph and readouts.
Think of it this way
Change one input while keeping the others fixed, as you would in a controlled experiment.
Worked example
Helium4 atomic mass4.002603 u gives binding≈28.296 MeV.
Why this matters
The model connects mass defect and binding with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
A positive mass defect corresponds to?
- Energy creation from nothing
- Positive binding energy
- Negative nucleon count
Read the explanation
The bound state is lower in energy by Δmc².
Course connection: Class XII Chapter 13. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.