P1+2 Energy Flashcards
What are the energy pathways?
Heating, radiation, mechanical, electrical
What are the energy stores?
Chemical, thermal, kinetic, elastic, gravitational, electrostatic, nuclear
What is conservation of energy?
Energy can’t be created or destroyed, this applies to all energy changes.
What is a closed system?
A system in which no energy transfers take place out of or into the energy stores of the system.
Work done equation
work done, W(j) = force applied, F(n) x distance travelled, d(m)
What does energy transferred equal?
Work done.
Gravitational potential energy equation
GPE(j) = mass, m(kg) x gravitational field strength, g(N/Kg) x height, h(m)
Kinetic energy equation
1/2 x mass, m(kg) x speed^2, v^2 (m/s^2)
Elastic potential energy equation
1/2 x spring constant, K(N/m) x extension^2, e^2(m^2)
What is Useful energy?
Energy transferred to where it is wanted in the way it is wanted.
What is Wasted energy?
Energy that is not usefully transferred.
What happens to energy as it dissipates (spreads out)
It becomes less and less useful
Equation for efficiency
efficiency=useful output energy transferred by the device(j)/total input energy supplied to the device(j)
Equation for power
power, p(w) = energy transferred to appliance, e(j)/time taken for energy to be transferred, t(s)
Equation for specific heat capacity
Change in energy, ∆E(j) = mass, m(kg) x specific heat capacity, c(j/kg) x temperature change, ∆θ(°C)
What does the specific heat capacity of a substance mean?
The energy needed to change 1Kg of a substance by 1°C
What are examples of electrical appliances and why are they used?
They could be heating, lighting and producing sound. They can transfer energy quickly and efficiently so they do not waste energy.
What actually is power?
The energy you supply per second is the power.
How to calculate power wasted?
power wasted = total power in - useful power out
What are the best conductors of energy?
Metals
What is thermal conductivity?
Thermal conductivity is the rate at which energy is transferred through something by conduction.
What does insulation do to energy transfer?
The thicker the layer of insulating material, the lower the rate of energy transferring through.
What is infrared radiation?
It is part of the electromagnetic spectrum and is given out by the sun. All objects emit and absorb infrared radiation. It also increases the amount emitted with the heat.
What is black body radiation?
It is the radiation emitted by a perfect black body. It absorbs all the radiation incident on it.
What happens to infrared radiation if the body has a constant temperature?
It emits the same amount at the same rate as it absorbs it.
What are some factors affecting the temperature of the earth?
The rate that light and infrared radiation are reflected back into space or absorbed by the earths atmosphere or surface and emitted from the earths surface and atmosphere into space.
How can you reduce the rate of energy transfer from a home?
You can use loft insulation(fibreglass), you can use cavity wall insulation reducing the amount of energy transfer by conduction, you can use aluminium foil between a radiator and a wall to reflect radiation away from the wall, you can use double glazed windows and you can use external walls with thicker bricks and lower thermal conductivity
How do solar panels work?
They absorb infrared radiation from the sun and are used to generate electricity directly or to heat water directly.
