P2 Energy transfer by heat Flashcards
What is thermal energy?
An energy store due to the movement of particles that make up an object.
What does the amount of thermal energy in an object depend on?
• The mass of the material
• What the material is made of
• The temperature of the material
What is temperature?
• A measure of how hot or cold something is.
• A measure of the average kinetic energy of the particles in a material.
• The more kinetic energy the particles have the higher the temperature of the object.
What is heat?
The transfer of energy from the thermal energy store of an object at a higher temperature to the thermal energy store of an object at a lower temperature.
What are the ways heat can transfer?
- Conduction
- Convection
- Radiation
- Evaporation
How are heat and temperature linked?
• Heat is transferred from a hot object to a colder object.
• Heat only flows when there is a temperature difference.
• Heat will continue to flow until 2 objects are at the same temperature. We say the objects are in thermal equilibrium.
What is thermal conductivity?
• A measure of the rate at which a material conducts energy from a thermal store.
• The higher the thermal conductivity of a material the higher the rate of energy transfer through it.
• A material with a high thermal conductivity is a good conductor, a material with a low thermal conductivity is a good insulator.
What does thermal conduction through an object depend on?
• The thermal conductivity of the material.
• The thickness of the material. (The thicker the material the lower the rate of transfer.)
• The temperature difference across the material. The bigger the difference the greater the rate of transfer.
Explain how thermal conduction happens when we heat a rod.
• The solid is made up of particles.
• These particles are always vibrating.
• As we heat the rod, the particles vibrate more.
• They bump into each other, transferring energy.
• The entire rod eventually heats up.
What is a fluid?
A fluid is either a liquid or a gas. The particles in a fluid can flow.
Why are fluids poor conductors?
Fluids are poor conductors (compared to solids) because particles in these states are further apart. As there is more space between the particles there are fewer collisions between the particles so energy is not transferred.
What does the energy required to raise the temperature of a material depend on?
• What the material is made of
• The mass of the material
• How much you want to raise the temperature by
What is the ‘Specific Heat Capacity’ of a substance?
The amount of energy in Joules needed to raise the temperature of 1 kilogram of a substance by 1 degree Celsius.
State the units for Specific Heat Capacity.
J/Kg °C Joules/Kilogram Degree Celsius
What is the equation for change in thermal energy of a substance?
Change in thermal energy = Mass x specific heat capacity x change in temperature
∆E=m x c x ∆θ
Give SI units for all quantities involved.
Energy (J), Mass(kg), Specific heat capacity J/Kg °C Joules/Kilogram Degree Celsius, change in temperature (°C)
State ways of insulating homes.
• Cavity wall insulation
• Loft insulation
• Double glazing or curtains
• Carpets
• Draft excluders
Explain what loft insulation is and how it works.
Layer of insulating material over/under loft floor (or between rafters). Convection causes warm air to rise to top of house; insulation slows conduction of heat through ceiling into loft (and then to the outside).
Explain what cavity insulation is and how it works.
Layer of insulating material between inner and outer walls. Slows conduction of heat; from rooms to outside.
Explain what double glazing is and how it works.
Two panes of glass in windows with air/vacuum in space between. Air/vacuum are good insulators; so slow conduction of heat from rooms through windows to outside air; and vacuum also prevents heat transfer by convection.
What is infrared radiation?
Infrared radiation (like visible light) is part of the family of waves called the electromagnetic spectrum.
We cannot see it with our eyes. Infrared radiation has a longer wavelength than light.
How is infrared radiation linked to heat?
All objects emit and absorb infrared radiation. The hotter an object, the more infrared radiation it emits in a given time.
