Energy Flashcards
What is the law of conservation of energy?
Energy can be transferred usefully, stored or dissipated but can never be created or destroyed
What is a closed system?
A system where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero
Energy can be transferred between stores in what four ways?
- Mechanically - object moving due to a force
- Electrically - a charge or current moving through a potential difference
- Heating
- Radiation
What is the energy store when an object is moving?
Kinetic energy store
When is energy transferred to the kinetic energy store?
When a object speeds up and is transferred away from this store when an object slows down
What is work done?
The energy transferred when a force moves an object through a distance, or by a moving charge
What are the energy transfers when a ball rolls down a ramp?
The ball does work again to overcome friction
Energy is transferred to thermal and sound energy and wasted
When an object falls and there is no air resistance, what happens to the gpe and kinetic energy store?
Energy lost from the g.p.e store = energy gained in the kinetic energy store
The energy in the elastic potential energy store of a string can be found using 1/2ke^2 as long as….?
the limit of proportionality has not been exceeded
What is the definition of specific heat capacity?
The amount of energy needed to raise the temperature of 1kg of a substance by 1 degrees Celcius
What are the units of specific heat capacity?
J/kg°C
How do you investigate specific heat capacity?
- Measure the mass of the block then wrap it in an insulating later
- Inset the thermometer and heater into the block where there should be holes on the lid
- Measure the initial temperature of the block and set the potential difference of the power supply to be 10V
- Turn on the power supply and start a stop watch and as the block heats up, take readings of the temperature and current every 10 minutes.
- Using your measurement of the current and the potential difference of the power supply, you can calculate the power of the heater using P= IV and then use this to calculate how much energy has been transferred by E = Pt
- Then use different materials and see how their specific heat capacities compare
What is power?
Power is the rate at which energy is transferred or the rate at which work is done
What is one Watt equivalent to?
1 joule transferred per second
What are the two equations for efficiency?
useful output energy/total input energy
useful power output/total power input
How do you improve the efficiency of energy transfers?
- Insulating objects
- Lubricating them
- Making them more streamlined
What are the main energy resources available for use on Earth?
- fossil fuels (coal, oil, gas)
- nuclear
- bio fuel
- wind
- hydroelectricity
- tidal
- solar
- geothermal
What is a renewable energy resource?
One that is being, or can be, made at the same rate (or faster) than it’s being used so it never runs out.
What are some of the uses of energy resources?
- transport
- electricity generation
- heating
The higher the thermal conductivity of a metal….
The higher the rate of energy transfer by conduction across a material
What factors affect the rate of heat transfer across a material?
- SA
- Type of material
- Temperature difference across a material
- Thickness of a material
- Conductivity of a material
As the thickness of a wall increases, what happens to the rate of flow?
Decreases
As the rate of conductivity increases, what happens to the rate of flow?
Increases
Why are cavity walls good insulators?
Air gap in the middle reduces the amount of energy transferred by conduction through the walls because air is an insulator - can also reduce energy transfer by convection
