P1 Flashcards
Conservation and dissipation of energy
Name the 5 energy stores
- chemical energy store
- kinetic energy store
- elastic potential energy store
- gravitational potential energy store
- thermal energy store
Draw a flow diagram for the energy transfers when a torch is turned on
- chemical energy store in battery
-> electric current in wires (kinetic energy)
-> energy transferred to the environment as light energy and some waste thermal energy
Draw a flow diagram for the energy transfers in an AU where Jayce kills himself and isn’t stopped by Viktor
- gravitational potential energy store as he stands on the bombed out balcony
-> kinetic energy (jumps off and is falling)
-> heating and sound on impact (his blood covers the streets of Piltover)
What is the law of conservation of energy ?
energy cannot be created or destroyed (only transferred/dissipated/stored)
What is a closed system ?
A system in which no energy transfers into or out of the system’s energy stores take place
- energy transfers can take place between these
[] a good example would be a pendulum in a vacuum (where there would be no air resistance)
What is work done ?
total energy transferred
What is work done (equation) ?
work done (J) = force (N) x distance moved along line of action of force (m)
What is special about work done to overcome friction ?
mainly transferred to thermal energy stores of the objects rubbing and the environment via heating
Give the equation for the change in gravitational potential energy (using weight and change of height)
gp (J) = weight (N) x change (m)
Give the equation for the change in gravitational potential energy STORE (using mass, gravitational field strength and change of height)
gp STORE (J) = mass (kg) x gfs (N/kg) x change in height (m)
What does the kinetic energy store of an object depend on ?
- mass
- speed its moving at
Give the equation for the kinetic energy store of an object
kinetic energy store (J) = 0.5 x mass (kg) x (velocity (m/s))^2
What is Hooke’s law ?
The force applied to a spring is directly proportional to its extension
Give the equation for elastic potential energy
epe (J) = 0.5 x spring constant (N/m) x (extension (m))^2
What is useful energy ?
energy transfers that are INTENDED to happen
- eg. energy transfer to light in a torch, heat in a radiator, sound in a speaker etc.
What is wasted energy ?
energy transfers that are NOT INTENDED to happen
- eg. heat from a lightbulb, sound from a laptop etc.
- these reduce energy efficiency of a system or an appliance etc.
What happens to all energy eventually (if not in a closed system) ?
dissipates
- as energy dissipates, it gets less useful
What is input energy ?
Total energy supplied to the device
Give the equation for efficiency
efficiency = (useful output energy/total input energy) x 100
What is efficiency ?
How much input energy is outputted as useful energy
- a machine can only ever be 100% efficient, as you cannot get more energy out of a machine than you put into it (law of conservation of energy)
How can you make a machine that has a lot of waste energy due to friction more efficient ?
Lubricate the moving parts
How do you reduce energy waste in electrical circuits with wires that have a high resistance and cause heat to be emitted ?
Use wires with less resistance
How can you reduce wasted energy for a vehicle/machine that has to overcome air resistance in order to work ?
Streamline the shape as much as possible to reduce air resistance and increase the availability of energy to be used for useful energy outputs
How do you reduce wasted energy for a machine that makes a lot of (unwanted) noise ?
Cut out the noise by tightening loose parts to reduce vibration etc.
What are the majority of everyday electrical appliances powered by ?
gas, oil, electricity
Give the useful and wasteful energy outputs of 3 everyday appliances
- lightbulb
[] useful = light
[] wasteful = heat - kettle
[] useful = heat for heating water
[] wasteful = sound, heating the actual kettle and not the water - hairdryer
[] useful = kinetic energy of air driven by fan, heating air when it flows past the heating filament
[] wasteful = heating the hairdryer casing, noise
What is power ?
the rate at which energy is transferred, measured in watts (W)
What is power (equation) ?
power (W) = energy to appliance (J)/time taken for transfer (s)
Give the equation for efficiency using power
efficiency = (useful power out/total input energy) x 100
