# Physics - Thermal Physics

> Source: https://ollybritton.com/notes/a-level/physics/topics/thermal-physics/ · Updated: 2021-09-06 · Tags: school, year-2

## See Also
- [Physics - Ideal Gases](https://ollybritton.com/notes/a-level/physics/topics/ideal-gases/)
- [Physics - Recall for Chapter 15: Ideal Gases](https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-15-thermal-physics/)
- [Physics - Recall for Chapter 14: Thermal Physics](https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-14-thermal-physics/)

## Flashcards
##### What two points define the Kelvin scale??
* Absolute zero
* Triple point of water

##### What is the triple point of water??
The point at which water is a solid, liquid and gas simultaneously.

##### How can you have a solid, liquid and a gas simultaneously??
By setting an exact pressure and temperature.

##### What is $0K$ in Celsius??
$$
-273.15^\circ
$$

##### What is $0^\circ$ in Kelvin??
$$
273.15K
$$

##### What is the equation for converting Kelvin $T$ to Celsius $\theta$??
$$
T = \theta + 273.15
$$

##### What is the equation for converting Celsius $\theta$ to Kelvin $T$??
$$
\theta = T - 273.15
$$

##### What does it mean for two objects to be in thermal equilibrium??
There is no net transfer of thermal energy between them.

### 2021-09-10
##### What is the kinetic model??
The explanation of solids, liquids and gasses as substances made up of atoms.

##### What is the order of solids, liquids and gasses for increasing potential energy??
* Solid
* Liquid
* Gas

##### What is the maximum potential energy in a gas??
$$
0J
$$

##### What force holds molecules together in solids and liquids??
The electrostatic force.

##### What causes Brownian motion in things like smoke or pollen particles??
Collisions with smaller, hard to see particles.

### 2021-09-13
##### Why does heating an object at a state change not increase its temperature??
All energy is going towards potential energy rather than kinetic energy.

##### What is the $\text{internal energy}$ equation??
$$
\text{internal energy} = \text{kinetic energy} + \text{potential energy}
$$

##### What is the wordy definition of internal energy??
The sum of the randomly distributed kinetic and potential energies of atoms or molecules in a substance.

##### Energy supplied to an object is increasing the kinetic energy. What happens as a consequence??
The temperature increases.

##### Energy supplied to an object is increasing the potential energy. What happens as a consequence??
The object is changing state.

##### Why is the potential energy the highest at $0J$ in a gas??
Because no work is needed to pull the particles apart.

##### Why is the potential energy the most negative in a solid??
Because you need to do a lot of work to pull the particles apart.

### 2021-09-18
##### What is the specific heat capacity of a substance??
The energy required to raise a $1kg$ mass by $1K$.

##### What is the equation for the specific heat capacity of a substance $c$??
$$
c = \frac{E}{m\Delta\theta}
$$

##### What is the equation for the energy $E$ required to heat by $\Delta\theta$??
$$
E = mc\Delta\theta
$$

##### What are the units for specific heat capacity??
$$
J\\,kg^{-1}\\,K^{-1}
$$

##### What's the equation for the specific heat capacity of a material after supplying $V$ volts at $I$ amps for $t$ seconds to a mass $m$ and finding a temperature difference $\theta_2 - \theta_1$??
$$
c = \frac{VIt}{m \times (\theta_2 - \theta_1)}
$$

### 2021-10-12
##### What is the method of mixtures??
A technique for determining the specific heat capacity of a material by measuring the final equilibrium temperature when added to another substance.

##### What principle allows you to use the method of mixtures??
$$
\text{energy lost by one object} = \text{energy gained by other object}
$$

(at thermal equilibrium)

##### What is true about the final equilibrium temperature of two different objects??
It is equal.

### 2021-10-14
##### What is the equation for the energy of a state transition (specific latent heat)??
$$
E = mL
$$

##### What are the units for $L$, the specific latent heat??
$$
J\text{kg}^{-1}
$$

##### What is $L_f$ in relation to specific latent heat??
The specific latent heat of fusion.

##### What is $L_v$ in relation to specific latent heat??
The specific latent heat of vaporization.

##### What is the specific latent heat of fusion??
The energy gained or lost at the solid/liquid state transition.

##### What is the specific latent heat of vaporization??
The energy gained or lost at the liquid/gas state transition.

##### How would you calculate the energy required to heat water to $120^{\circ}$ from $20^{\circ}$??
$$\text{the energy to 100 + energy for state transition + energy to 120}$$

##### What is the specific latent heat of fusion for water??
$$
334kJ
$$

##### What is the specific latent heat of vaporization for water??
$$
2260kJ
$$

##### What's normally bigger: the specific latent heat of fusion or the specific latent heat of vaporization??
The specific latent heat of vaporization.

### 2022-01-08
##### What is Boyle's law??
$$
\text{pressure} \times \text{volume} = \text{constant}
$$

##### What is Charles's law??
$$
\frac{\text{volume}}{\text{temperature}} = \text{constant}
$$

##### What is the pressure law/Gay-Lussac's law??
$$
\frac{\text{pressure}}{\text{temperature}} = \text{constant}
$$

##### What is an isochoric change in a gas??
Where the volume of the gas remains constant.

### 2022-01-20
##### What is true about the mean kinetic energy of particles for two objects in thermal equilibrium (e.g. a metal container of water)??
It is equal.

##### How should you describe the movement of particles in a solid??
Vibrating about a fixed point.

##### How should you describe the movement of particles in a liquid??
Moving freely past each other (not just moving freely) randomly.

##### How should you describe the movement of particles in a gas??
Moving freely.

### 2022-03-02
##### What must you specify about an electric heater in a question about specific heat capacity??
That it is fully immersed in the medium.

### 2022-03-07
##### How can you justify that the potential energy of a gas is larger than that of a liquid??
Energy must be supplied to a liquid to change its state.

### 2022-03-08
##### What's better than saying "heat is lost to the surroundings"??
Heat is lost to _something specific_.

##### When describing how pressure comes about using particle collisions with container walls, what must you add after showing particles exert a force on the container walls??
That pressure is the sum of these forces over the area.

##### What is one potential reason all the energy from a laser might not be transmitted to a metal??
Reflection on the surface of the metal.

### 2022-04-14
##### Given the molar masses of two gases, and the mean speed of one of the gases at a certain temperature, how could you work out the mean speed of the other gas at the same temperature??
Use the fact that $\frac{1}{2} mv^2$ must be equal for both.

##### How does Brownian motion provide evidence for gas molecules continuously moving??
The larger particles are continuously moving.

##### How does Brownian motion provide evidence for a large number of gas molecules??
The overall movement is small due to molecules hitting from all sides.

### 2022-05-03
##### When describing the practical for determining the specific heat capacity of a liquid, what must you connect across the heater??
A voltmeter.

### 2022-05-04
##### "The molecules are in a tight, fixed lattice due to the electrostatic forces..." No. What should it be instead??
"strong electrostatic forces"

##### Why is there still a transfer of thermal energy between two objects at equilibrium??
Energy is always being transferred but it's only when there is a temperature difference that there is a _net_ transfer.

##### "In a liquid, molecules are no longer tightly bound..." No. What should it be instead??
Closely packed due to fairly strong electrostatic forces.

##### What can you match up in terms of kinetic energy, potential energy, molecule speed and molecule separation in a substance??
* Kinetic energy increases with molecule speed
* Potential energy increases with molecule separation

##### "Specific latent heat of fusion is the energy required to change the temperature of a substance from solid to liquid per unit mass..." No. What is an important clarification when defining latent heat??
"Without changing its temperature"

---
Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt