physics p5 Flashcards
what is energy
a quantity (joules) that tells you what is possible and doesn’t tell you what will happen
what are the types of energy stores
chemical
thermal
kinetic
gravitational
magnetic
elastic
nuclear
electrostatic
what is an example of a chemical energy store
pile of coal with oxygen
glucose in muscles with oxygen
give example of thermal energy store
hot bath
give example of kinetic energy store
moving car
give example of gravitational energy store
a skier at top of a hill
give example of elastic potential energy
stretched elastic band
give example of nuclear store
hydrogen in the sun
lump of uranium
how is energy transferred?
between different stores:
mechanically
electrically
heating
radiation
what is the law of conservation of energy
energy cannot be created or destroyed. It can only be transferred between stores.
How does an electric current transfer energy?
It transfers energy when charges moves from a chemical potential store to a device like lamp
What does the power rating of an appliance tell you?
It tells you the rate at which they transfer energy between stores
what units are work done measured in
Joules (J) or kilowatt-hour (KWh)
what do electrical appliances do?
transfers energy electrically from chemical stores for a particular job
How do appliances change energy between stores?
transfer energy from one store to another
What are the steps to analyzing an energy transfer system?
- identify start and end points of what it is doing e.g turned on or off
- identify stores e.g kinetic
What are two ways to increase energy in a thermal store?
- Burning a fuel
- Using an electric current to transfer energy
What causes a temperature difference?
A temperature difference produces a transfer of energy from a hot object to a cool object until it is in equilibrium
what does ‘in equilibrium’ (thermal) mean?
when two objects reach the same temperature and no more energy is transferred between them
How do storage heaters work?
it contains a large piece of concrete that heats up during the night so in the day, it cools down and heats the house
What is energy dissipation?
when energy spreads out to the surroundings (usually thermal) making it less useful.
What happens to energy after watching TV or drying clothes?
dissipates as thermal energy into the surroundings
How can energy dissipation be reduced?
- Using lubrication to reduce friction (e.g. using oil)
- Using insulation to reduce heat transfer (e.g., foam in walls)
what is efficiency?
a measure of how good a device is at changing energy from one form to another
how to calculate efficiency
useful energy out / total energy in x100
(smaller/bigger) x100
