Define thermal energy:
The energy possessed by an object due to its temperature
Define temperature:
Temperature is a measure of the average kinetic energy of the particles in a substance
How is thermal energy transferred?
It is transferred from a region of higher temperature to a region of lower temperature and energy will continue to be transferred until both regions are the same temperature
What is a thermometer?
A thermometer is any device that uses a physical quantity that varies with temperature to measure temperature
List the physical quantities that vary with temperature:
- The density of a liquid
- The volume of a gas at constant pressure
- Resistance of metal
- EMF of a thermocouple
At what two points are thermometers calibrated to?
0 and 100 or melting and boiling point
Define specific heat capacity:
The amount of thermal energy required to raise the temperature of 1kg of a substance by 1°C
What is the specific heat capacity equation?
ΔQ = mcΔθ
ΔQ = change in thermal energy in J
m = mass of the substance you are heating up in kg
c = specific heat capacity of the substance in Jkg-1K-1or Jkg-1 °C-1
Δθ = change in temperature in K or °C
Define specific latent heat:
The thermal energy required to change the state of 1kg of mass of a substance without any change in temperature
State the difference between SLH of fusion vs vaporisation:
SLH of fusion = is the heat energy required to convert a solid into a liquid at its melting point
SLH of vaporisation = is the heat energy required to convert a liquid into a gas at its boiling point
What is the equation for specific latent heat?
Q = Lm
Q = amount of thermal energy to change the state in J
L = latent heat of fusion or vaporisation in Jkg-1
m = mass of the substance changing state in kg
What is the specific heat capacity of water?
Specific heat capacity = 4200 Jkg-1K-1or Jkg-1 °C-1
What are the specific latent heat values of water?
Specific latent heat of fusion = 330 kJkg-1
Specific latent heat of vaporisation = 2.26 MJkg-1
What is thermal equilibrium?
For two objects in physical contact, thermal equilibrium occurs when there is no net transfer of thermal energy between regions and both regions reach an equal temperature
How does a liquid-in-glass thermometer work?
- This type of thermometer depends on the density change of a liquid (usually mercury)
- The thin glass capillary tube containing the liquid which expands with temperature with the scale being read based on the length of liquid within the tube
How does a gas thermometer work?
- It is based on Charle’s law where the volume of an ideal gas is directly proportional to its temperature when at constant pressure
- As the temperature of the gas increases so does the volume and vice versa
- A temperature scale can be made depending on how quickly the gas expands with temperature
How does a thermistor measure temperature?
- Thermistors are based on the principle that resistance and temperature are inversely proportional to each other
- The degree of the change in resistance can reveal the temperature change
What is a thermocouple?
- A thermocouple is an electrical device used as the sensor of a thermometer
- It consists of two wires of different metals attached to each other to create two junctions while the other end of the wires is connected to a voltmeter
How does a thermocouple work?
- When there is a temperature difference between the junctions, am EMF is produced between the two free ends of the wires and measured by the voltmeter
- The greater the difference in temperature between the wires, the greater the EMF
- The thermocouple requires calibration since the EMF does not vary linearly with temperature
What does the graph of EMF against temperature look like?
The graph of EMF against temperature is a positive, curved line
How do you convert between degrees celsius and kelvin?
- °C = K − 273.15
- K = °C + 273.15
What is meant by absolute zero?
It is the lowest possible temperature on the thermodynamic temperature scale or at zero Kelvin; it is when the average kinetic energy of the molecules is zero
