Energy Flashcards
What is the unit of energy?
Joules (j)
Where does some of the energy in chemical reactions go?
Transfered to surroundings as heat
Everything emits and absorbs what?
Infrared radiation
What is the best surface for absorbing infrared radiation?
What is best surface for emitting infrared radiation?
Absorbing = shiny, light coloured surfaces
Emitting = black, matt surfaces (reflects it)
Explain, in terms of radiation, how objects cool and how they warm up
Absorb and emit radiation at same time
If emits faster than absorbs -> cools
If emits slower than absorbs -> warms
Explain how, in terms of particles, melting happens
Particles vibrate when heated
Bonds between atoms weaken
Solid -> liquid
Explain how, in terms of particles, evaporation happens
Particles vibrate when heated
Bonds between atoms break
Particles move around randomly
What is conduction?
How does it work?
Transfers energy through a solid
Particles in heated end vibrate into each other transferring the energy from one atom to another
What type of materials are the best conductors?
Why is this?
Metals
Metals have free electrons in their structure
Free to move rapidly and transfer heat energy
What is convection?
How does it work?
How heat spreads through a liquid or a gas
When one part is heated, the particles vibrate taking up more space.
Warm part expands - less dense, rises above cool part
This is called convection currents
What is the water cycle?
Water evaporates from the Earth’s surface
Cools -> clouds
Water vapour condenses -> rain
How is energy transferred when an object cools?
Transferred to surface by conduction
From surface by convection
What are the two factors that affect the rate of energy transfer?
Heat - hotter objects lose energy quicker
Greater surface area to volume - energy transferred quicker
How do you calculate the amount of energy transferred from an object?
Energy = Mass x Specific Heat Capacity (J/kg) x Temp change (°C)
What is waste energy?
Any transferred to surroundings = waste energy
