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Friday, 9 October

JEE Main 2020 · PhysicsMultiple choiceDiagram basedMediumData or graph

JEE Main 8 January 2020, Shift 1, Physics Q9

Question 9 of 75 in this shift, Physics question 9 of 25, Section A.

The plot that depicts the behavior of the mean free time τ\tau (time between two successive collisions) for the molecules of an ideal gas, as a function of temperature (T), qualitatively, is : (Graphs are schematic and not drawn to scale)

The figure, in words

Four candidate graphs of mean free time against T, sqrt(T), 1/sqrt(T), 1/T (see options).
  1. (1)[figure: graph of τ\tau vs TT, straight line increasing]
  2. (2)[figure: graph of τ\tau vs T\sqrt{T}, straight line decreasing]
  3. (3)[figure: graph of τ\tau vs 1T\frac{1}{\sqrt{T}}, straight line increasing]Official answer
  4. (4)[figure: graph of τ\tau vs 1T\frac{1}{T}, straight line increasing]

Official answer

Option 3

NTA final key (Jan 2020).

Chapter
Kinetic Theory
Topic
Kinetic Theory of Gases
Idea tested
Relaxation Time

Same idea in other shifts

Asked 3× in all
  1. 9 Jan 2020, Shift 2 · Q10Two gases - argon (atomic radius 0.07 nm, atomic weight 40) and xenon (atomic radius 0.1 nm, atomic weight 140) have the same number…MediumSingle correct
  2. 6 Sep 2020, Shift 2 · Q9In a dilute gas at pressure P and temperature T, the mean time between successive collisions of a molecule varies with T as :MediumSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.