Flashcards in Thermal Physics Deck (21)
State the distinguishing properties of solids, liquids
- Do not flow
- Fixed volume
- Cannot be compressed
- Shape stays the same
- Fixed volume
- Cannot be compressed
- Fill shape of container
- No definite volume
- Can be compressed
- Take shape of container
Describe the molecular structure of
solids, liquids and gases and relate it to the forces and distances between molecules and to the motion of
- Particles are close together, help together by strong intermolecular forces -> particles vibrate around a fixed point, so has little freedom of movement.
- 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
- Particles are far apart -> move freely
Describe change of temperature on the pressure of a gas at constant volume
Pressure is directly proportional to temperature.
Higher temp -> higher pressure
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
Definition of evaporation
The escape of more-energetic molecules from the surface of a liquid
How to increase evaporation?
- Create more wind/ draught across the surface
- Increase surface area
- Increase the temperature
Relate evaporation to the consequent cooling
Increase temp of liquid -> particles with higher kinetic energy -> leave surface easier -> average energy falls -> drop in temperature
pV = constant at constant temp
Order of magnitude of the expansion of solids, liquids and gases
Gas -> liquid -> solid
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
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)
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
Distinguish between boiling and evaporation
- Bubbles are formed
- Occurs throughout the liquid
- Occurs at a definite temp
- Source of energy needed
- No bubbles formed
- Take place only from the exposed surface
- Occurs at all temp
- Energy supplied from surroundings
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
2. freezing/ solidification
What is meant by latent heat?
The energy supplied to a substance when it changes its state
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
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
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.
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.
Describe experiments to show the
properties of good and bad emitters
and good and bad absorbers of infra-red
- 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.