Key relationship
λ=1/(√2πd²n); N=nV; amount=N/NA.
Physics · Class 11
Change molecular collision density
Mean free path is the average travel distance between molecular collisions. Higher number density or larger collision diameter makes collisions more frequent. Avogadro number converts the counted particles to moles.
Open the interactive experiment →Change molecular collision density
மூலக்கூறு மோதல்களுக்கு இடையிலான சராசரி தொலைவு சராசரி கட்டற்ற பாதை. அடர்த்தி அதிகரித்தால் அது குறையும்.
Key notes, relationships and model limits
Remember
Mean free path is the average travel distance between molecular collisions. Higher number density or larger collision diameter makes collisions more frequent. Avogadro number converts the counted particles to moles.
Common trap
Mean free path is an average distance, not the same path length for every molecule.
Model limits
Dilute hard-sphere gas with random molecular motion. The √2 accounts for relative motion; collision diameter is an effective model parameter.
What you will learn
Relate collision geometry, number density and molecular counting.
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
At d=3 Å and n=2.5×10²⁵ m⁻³, λ≈1.00×10⁻⁷ m. In 10 L there are 2.5×10²³ molecules, or about 0.415 mol.
Why this matters
The model connects change molecular collision density with an observable reading. Check the equation and assumptions before applying it.
Before you start
SI units · algebra · graph reading
Check your understanding
If number density doubles, what happens to mean free path?
- It doubles
- It halves
- It remains fixed
Read the explanation
λ is inversely proportional to number density.
Course connection: Class XI Chapter 12. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.