OCR A-Level Physics A H556
Practical Skills in the Written Papers
The Practical Endorsement
Physical Quantities and Units
Making Measurements and Analysing Data
Nature of Quantities
Motion
Forces in Action
Work, Energy and Power
Materials
Newton’s Laws of Motion and Momentum
Charge and Current
Energy, Power and Resistance
Electrical Circuits
Waves
Quantum Physics
Thermal Physics
Oscillations
Gravitational Fields
Astrophysics and Cosmology
Capacitors
Electric Fields
Electromagnetism
Nuclear and Particle Physics
Thermal Physics
Maxwell-Boltzmann distribution, Boltzmann constant and internal energy
- 2 things to know
- Papers 1, 2 and 3
Overview
Recall questions on the Maxwell-Boltzmann distribution and how temperature changes it, the Boltzmann constant, pV = NkT, deriving mean kinetic energy = 3/2kT, and the internal energy of an ideal gas.
What you need to know
Answer each one before you reveal it.
What does the Maxwell-Boltzmann distribution describe?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Describe the shape of the Maxwell-Boltzmann distribution curve.
Model answer
It is asymmetric with a tail extending to high speeds
- 2
In the Maxwell-Boltzmann distribution, how do the most probable speed, mean speed, and rms speed compare?
Model answer
The most probable speed is less than the mean speed, which is less than the rms speed
- 3
State the equation relating the mean translational kinetic energy of a gas molecule to temperature.
Model answer
(1/2)m⟨c²⟩ = (3/2)kT, where m is the mass of a molecule, ⟨c²⟩ is the mean square speed, k is the Boltzmann constant, and T is absolute temperature
- 4
Starting from kT = (1/3)m⟨c²⟩, what operation yields the final form of the mean kinetic energy equation?
Model answer
Multiply both sides by 3/2 to obtain (3/2)kT = (1/2)m⟨c²⟩
- 5
What does the Maxwell-Boltzmann distribution describe?
Model answer
The spread (distribution) of molecular speeds in a gas
- 6
How does the Maxwell-Boltzmann distribution change when the temperature of a gas increases?
Model answer
The distribution becomes broader and the peak shifts to higher speeds
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