1. The transfer of energy by heating processes
Energy transfer by heating processes
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2. Overview
Energy can be transferred from one place to another by work or by heating processes.
We need to know how this energy is transferred and which heating processes are most important in a particular situation.
What is the difference between heat and temperature?
What are the three ways in which thermal energy can be transferred?
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3. Infrared radiation 1
All objects emit and absorb infrared radiation. The hotter an object is, the more infrared radiation it radiates in a given time.
What surfaces are the best and worst radiators of infrared radiation?
Which surfaces are the best and worst absorbers of infrared radiation?
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4. Infrared radiation 2
Dark, matt surfaces are good absorbers and good emitters of infrared radiation.
Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation. Light, shiny surfaces are good reflectors of infrared radiation.
Explain why:
cricketers wear white clothes
matt, black is the best colour for a motorbike engine
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5. Kinetic theory
The particles of solids, liquids and gases have different amounts of energy.
Solid
Liquid
Gas
Explain the difference in structure of solids, liquids and gases in terms of the energy the molecules have.
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6. Energy transfer by heating
The transfer of energy by conduction, convection, evaporation and condensation involves particles.
Conduction is the transfer of energy from one molecule to another.
Convection is the movement of heated molecules.
Why are metals better conductors than gases?
What are convection currents and why do they occur?
A convector heater
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7. Evaporation and condensation
The factors that affect the rate of evaporation and condensation are:
temperature
wind
humidity
surface area
How do these factors affect the rates of evaporation and condensation?
Graph of particles in a liquid
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8. Rate of transfer of energy
The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.
Explain the features of a vacuum flask that reduce energy transfer.
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9. Heating and insulating buildings 1
U-values measure how effective a material is as an insulator.
The lower the U- value, the better the material is as an insulator.
Which materials used for building have low U-values?
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10. Heating and insulating buildings 2
Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water.
What are the advantages and disadvantages of solar panels for heating?
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11. Heating and insulating buildings 3
The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius.
Is it best to fill solar panels with a fluid with a high or low specific heat capacity?
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12. Heating and insulating buildings 4
The formula is:
E = m  c  θ
where
E is energy transferred in joules, J
m is mass in kilograms, kg
θ is temperature change in degrees Celsius, °C
c is specific heat capacity in J/kg°C