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Flashcards in Thermal Physics Deck (21)
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1

State the distinguishing properties of solids, liquids
and gases

Solid:
- Do not flow
- Fixed volume
- Cannot be compressed
- Shape stays the same
Liquid:
- Flow
- Fixed volume
- Cannot be compressed
- Fill shape of container
Gas:
- Flow
- No definite volume
- Can be compressed
- Take shape of container

2

Describe the molecular structure of
solids, liquids and gases and relate it to the forces and distances between molecules and to the motion of
the molecules

Solid:
- Particles are close together, help together by strong intermolecular forces -> particles vibrate around a fixed point, so has little freedom of movement.
Liquid:
- Particles are also quite close together, forces are quite strong (but not as close and strong as solids)-> particles can move and slide over each other
Gas:
- Particles are far apart -> move freely

3

Describe change of temperature on the pressure of a gas at constant volume

Pressure is directly proportional to temperature.
Higher temp -> higher pressure

4

Describe the pressure of a gas in terms of the motion of its molecules

Gas pressure = number of particles hitting the wall of the object

5

Definition of evaporation

The escape of more-energetic molecules from the surface of a liquid

6

How to increase evaporation?

- Create more wind/ draught across the surface
- Increase surface area
- Increase the temperature

7

Relate evaporation to the consequent cooling

Increase temp of liquid -> particles with higher kinetic energy -> leave surface easier -> average energy falls -> drop in temperature

8

Pressure equation

pV = constant at constant temp

9

Order of magnitude of the expansion of solids, liquids and gases

Gas -> liquid -> solid

10

Demonstrate understanding of sensitivity,
range and linearity of a thermometer

- Range: lowest to highest temperature it can measure
- Sensitivity: the extent of change in the thermometric property for a rise in 1 degree Celsius. For e.g., alcohol expands x5 more than mercury for the same change of temp.
- Linearity: how far away your measurements are from the line

11

Definition of thermal capacity

The thermal capacity of an object is the energy that must be supplied to it to raise its temperature by 1 degree Celsius. Unit = J/(kg°C)

12

Describe an experiment to measure the specific heat capacity of a substance

Equipment: heater, thermometer, Joulemeter
- Record the mass
- Record the initial temperature
- Heat the substance
- Record the final temp and the energy supplied
- Use the equation: c = E/ m x temp change

13

Distinguish between boiling and evaporation

Boiling:
- Quick
- Bubbles are formed
- Occurs throughout the liquid
- Occurs at a definite temp
- Source of energy needed
Evaporation:
- Slow
- No bubbles formed
- Take place only from the exposed surface
- Occurs at all temp
- Energy supplied from surroundings

14

Name the process
1. Solid to liquid
2. Liquid to solid
3. Liquid to gas
4. Gas to liquid
5. Solid to gas
6. Gas to solid

1. melting
2. freezing/ solidification
3. evaporation
4. condensation
5. sublimation
6. condensation

15

What is meant by latent heat?

The energy supplied to a substance when it changes its state

16

Describe melting and boiling in terms of energy
input without a change in temperature

The two types of internal energy are potential and kinetic energy.
The kinetic energy is what defines the temperature of the substance. When the temperature of a substance reaches a state where it is ready to go through boiling/melting, energy is still being transferred but the temperature is still constant.
In this process, bonds are being broken/formed, therefore, potential energy increases

17

Use the terms latent heat of vaporisation and latent heat of fusion and give a
molecular interpretation of latent heat

Latent heat of vaporisation: liquid to gas
Latent heat of fusion: solid to liquid
if apply “energy” into the liquid/solid, the molecules inside (internal energy) starts to become more energetic and move around more often -> some of its molecules will have enough energy to overcome the forces of attraction holding the liquid/solid together, hence change of state happens

18

Give a simple molecular account of heat transfer in solids

Particles are fixed in regular structure and they cannot move. When the solid object is heated, its particles gain thermal and kinetic energy. But since they cannot move, they vibrate instead. As particles with more kinetic energy vibrate, they also pass on the vibration to other particles too.

19

Relate convection in fluids to density changes

If the bottom is gently heated, as the water above the flame becomes warmer, it expands and decreases in density. The less dense water rises as cooler, denser water sinks and takes its place, or we can say,This is a convection current.

20

Describe experiments to show the
properties of good and bad emitters
and good and bad absorbers of infra-red
radiation

- Place different materials of different colour under the sun, or close to a source heat radiation.
- After a period of time, measure their temperature. The dark surfaces should be warmer because they are better absorbers of infra-red radiation.

21

Identify and explain some of the everyday
applications and consequences of conduction,
convection and radiation

Conduction: pans, pots as the thermal energy is transferred through conduction
Convection: heater, air conditioner
Radiation: solar panels produce electricity by absorbing heat from sunlight by radiation