Energy Transfers by Heating Flashcards
What can the thermal conductivity of an object tell you?
How quickly energy is transmitted through it by thermal conduction
How can you test the thermal conductivity of rods of different metals?
- Each rod must have the same diameter and length
- Same temperature difference between its ends
- Place rods flat on a tripod
- One end of each rod covered in wax and the other ends heated equally using a bunsen burner
- The faster the wax melts, the higher the thermal conductivity of the metal
Why is it important to reduce the rate of heat loss from a building?
Heating bills can be expensive
What are 2 factors that can affect the rate of heat loss from a building?
- The thickness of its walls and roof
- The thermal conductivity of its walls and roof
How can the thermal conductivity of the walls and roof be reduced?
By using thermal insulators
What is a thermal insulator?
- A material that has a low thermal conductivity
- The rate of energy through an insulator is low
What are 3 things that the energy transfer per second through a material depends on?
- The material’s thermal conductivity
- The temperature difference between the two sides of the material
- The thickness of the material
What are 5 features that can be added to a house to reduce thermal conductivity?
- Loft insulation
- Cavity wall insulation
- Draught excluder
- Aluminium foil between a radiator panel and the wall
- Double-glazed window
What does temperature change depend on when a substance is heated or cooled?
- The substance’s mass
- The type of material
- How much energy is transferred to it
What is a material’s specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of the substance by 1 degree celsius
What is infrared radiation?
- Part of the electromagnetic system
- All objects emit (give out) and absorb (take in) infrared radiation
- The higher the temp, the more infrared it emits
- Good absorbers are also good emitters
What is infrared radiation like for an object at a constant temperature?
- Infrared radiation emitted = infrared radiation absorbed
- Infrared radiation is emitted across a continuous range of wavelengths
What happens to an object’s temperature when it absorbs infrared emission at a higher rate than it emits it?
It will increase
What does the temperature of the Earth depend on?
Rate at which visible light and infrared radiation are:
- Reflected
- Absorbed
- Emitted
By the Earth’s atmosphere and surface
What are examples of human activities that are increasing the amount of greenhouse gases in the Earth’s atmosphere?
- Burning fossil fuels
- Deforestation
- Livestock farming
What do greenhouse gases do?
- Absorb infrared radiation emitted by the surface of the Earth and prevent it escaping into space
- They then re-emit the infrared radiation back towards the surface of the Earth, increasing the Earth’s temperature
What are the greenhouse gases in the Earth’s atmosphere?
- Water vapour
- Carbon dioxide
- Methane
What is a black body?
- A theoretical object that absorbs 100% of the radiation that falls on it
- A perfect black body would not reflect or transmit any radiation
- Would also be a perfect emitter of radiation
How is radiation transmitted in the Earth’s atmosphere?
- Radiation from the Sun heats the Earth’s atmosphere
- Some radiation is emitted back into space
- Longer wavelength radiation emitted by the Earth’s surface is absorbed by greenhouse gases in the atmosphere
- Greenhouse gases re-emit radiation, increasing the temperature of the Earth
