Light & Matter

Question 1

Triple point of Water

Answer 1

The unique temperature and pressure at which water, water vapour, and ice coexist in equilibrium.
(Occurring at 0.01 C / 273.16 K

Question 2

Equipartition Theorum

Answer 2

When a substance is in equilibrium, there is an average energy of 1/2.kT per molecule or 1/2.RT per mole associated with each degree of freedom.

Question 3

Failure of the Equipartition Theorem

Answer 3

It fails if the thermal energy (~kT) that can be transferred in collisions is smaller than the energy gap dE between energy levels. E.g. monatomic gas molecules cannot rotate, because the first nonzero energy permitted is much greater than kT.

Question 4

1st Law of Thermodynamics

Answer 4

The change in the internal energy of the system equals the heat transfer into the system plus the work done on the system.

Question 5

When does Equipartition Theorem become inaccurate

Answer 5

When quantum effects are significant, such as at low temperatures.

Question 6

2nd Law of Thermodynamics: Clausius Statement

Answer 6

A process whose only net result is to Absorb heat from a cold reservoir and release the same amount of heat to a hot reservoir is impossible.

Question 7

2nd Law of Thermodynamics: Kelvin Statement

Answer 7

No system can absorb heat from a single reservoir and convert it entirely into work without additional net changes in the system or its surroundings.

Question 8

2nd Law of Thermodynamics: Heat-Engine Statement

Answer 8

It is impossible for a heat engine working in a cycle to produce only the effect of absorbing heat from a single reservoir and performing an equivalent amount of work.

Question 9

2nd Law of Thermodynamics: Refrigerator Statement

Answer 9

It is impossible for a refrigerator working in a cycle to produce only the effect of absorbing heat from a cold object and releasing the same amount of heat to a hot object.

Question 10

Refractive index n

Answer 10

Is the ratio of the speed of light in a vacuum to the speed of light in the medium.

Question 11

Dulong-Petit Law

Answer 11

The molar specific heat of most solids is 3R. This is predicted by the equipartition theorem, assuming a solid atom has 6 degrees of freedom.

Question 12

3 Conditions for a Reversible Process

Answer 12

1. No mechanical energy is transformed into internal thermal energy by friction, viscous forces, or other dissipative forces.
2. Energy transfer as heat can only occur between objects whose temperatures differ by an Infinitesimal amount.
3. The process must be quasi-static so that the system is always in an equilibrium state (or infinitesimally near an equilibrium state).

Question 13

Carnot Engine

Answer 13

A Carnot engine is a reversible engine that works between two heat reservoirs.

Question 14

Entropy

Answer 14

Is a measure of the disorder of a system.

Question 15

Focal Length

Answer 15

… is the image distance when the object is at infinity, so the incident light is parallel to the axis.