P1 - Energy Flashcards
How is energy transferred to an object?
When energy is transferred to an object, the energy is stored in one of the objects energy stores.
Energy is transferred mechanically (by a force doing work), electrically (work done by moving charges), by heating or by radiation (eg light or sound)
Name the energy stores:
- thermal
- kinetic
- gravitational potential
- elastic potential
- chemical
- magnetic
- electrostatic
- nuclear
What happens when a system changes?
Energy is transferred - can be transferred into or away from the system, between different objects in the system or between different types of energy stores.
What are closed systems?
Systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.
What is work done?
Another way of saying energy transferred. Work can be done when current flows (work is done against resistance in a circuit) or by a force moving on object.
What the formula for kinetic energy?
Ek = 1/2 x m x v2
Kinetic energy = 1/2 x mass x velocity2
Kinetic energy - (j)
Mass - (kg)
Velocity - (m/s)
Formula for gravitational potential energy:
GPE = m x g x (change in) h
GPE = mass x strength of gravity x change in height
GPE - (j)
Mass - (kg)
Strength of gravity - (N/Kg)
Height - (m)
Formula for elastic potential energy:
EPE = 1/2 x k x e2
EPE = half x spring constant x extension2
EPE - (j)
Spring constant - (N/m)
Extension - (m)
What is specific heat capacity?
The amount of energy needed to raise the temp of 1kg if a substance by 1’C.
Formula for specific heat capacity:
(Change in) E = m x c x temp change
Change in thermal energy = mass x specific heat capacity (SHC) x temp change
Thermal energy - (j)
Mass - (kg)
SHC - (j/kg)
Temp. - (‘C)
How much energy do you need to raise 1kg of water by 1’C?
4200J
How do you investigate SHC with a solid (eg copper)?
- need a block of material with two holes in – for the heater and thermometer to go in
1) measure mass of block, wrap in insulating layer - to reduce energy transferred from block to surroundings, insert thermometer + heater
2) measure initial temp. + set voltage (of power supply) to 10V, turn on power supply + start stopwatch.
3) when turn on power, current does work on the heater, transferring energy electrically from power supply to heaters thermal energy store. Energy then transferred to materials thermal energy store by heating, causing materials temp to increase.
4) As block heats up, take readings of temp + current every min for 10 mins. Current doesn’t change as block heats.
5) using measurement of current, voltage of power supply can calculate power supplied to heater at time of each temp reading using E = P x T - + time in secs since experiment began.
What is the observation of energy principle?
Energy is always conserved:
Energy can be transferred usefully, stores or dissipated, but can never be created or destroyed.
What is dissipated energy?
Sometimes called ‘wasted energy’ bc the energy is being stored in a way that isn’t useful (usually energy has been transferred into thermal stores)
What is power?
Power is the rate of energy transfer - measured in watts. 1 watt = 1J of energy transferred per second.
