energy Flashcards
what is the equation for kinetic energy?
1/2 x mass x velocity (squared)
what is the equation for elastic potential energy?
1/2 x spring constant x extension (squared)
what is the equation for gravity potential energy?
mass x gravitational field strength x height
define specific heat capacity of a substance
the amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree celsius.
state the units for specific heat capacity
joules
degree celsius
kilogram
what is the definition of power
the rate at which energy is transferred
or
rate at which work is done
state the two equations for power
power = energy transferred / time
power = work done / time
what is the unit of power
watt
two motors lift the same mass through the same height.
motor A does this in half the time of motor B
which dissipates the most power
motor a
the energy is transferred is the same but the time taken is less
describe the energy changes involved when a ball is thrown upwards and then returns to tis starting position.
upwards: KE is converted to GPE
peak: maximum GPE, zero KE
downwards: GPE is converted to KE
describe the energy transfers for a bungee jumper
- when falling, the GPE is converted to KE of jumper
- as cord tightens, KE is converted and stored as elastic potential energy
- at lowest point, the jumpers initial GPE equals the EPE stored in the cord
explain why a bungee jumper slows down once the cord begins to stretch
- kinetic energy decreases since it is converted to elastic potential energy
- since KE is proportional to velocity (squared), as KE decreases so does velocity
examples of chemical energy stores
- food
- fuel
- batteries
state 4 different stores of energy
- kinetic energy
- gravitational potential energy
- elastic potential energy
- chemical changes
state the law of energy conservation
energy cannot be created or destroyed (it can only be transferred into different forms)
state the changes in the total energy of a ball that is kicked, assuming that no external forces act
the total energy of the system remains constant due to the conservation of energy
what is waste energy
the energy that is not used by the device for its desired purpose
describe the energy changes that occur in a filament light-bulb
- electrical energy is transferred into light and heat energy
- light is a useful energy form, heat is a waste energy
state two equations to calculate efficiency
efficiency = useful output energy transfer / total input energy transfer
efficiency = useful power output / total power output
how can the efficiency of a system be increased
- reducing waste output (by lubrication or thermal insulation)
- recycling waste output (recycling thermal waste energy as input energy)
state the consequence for energy transfer of a material with a high thermal conductivity
the rate of energy transfer through the material is higher than for a material with a lower thermal conductivity
do double glazed windows have a higher or lower thermal conductivity than single glazed windows
lower, meaning less energy transfers through them
what key factors affect the rate of cooling of a building
- thickness of walls
- thermal conductivity of the walls
state three methods of reducing heat loss in a building
- double glazing
- loft and wall insulation
- thicker walls
how can the efficiency of a mechanical machine with moving parts be improved?
lubricate any moving parts to reuse the friction and therefore energy loss due to heating
how can the efficiency of a radiator be improved?
installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed into the walls
how can the efficiency of boiling water in a pan be improved
by placing a lid on the pan to reduce the heath loss from the top
what is a renewable energy resource
an energy source which can be used to replenish as it is being used up.
give 4 examples of renewable energy
- wind energy
- hydro-energy
- tidal energy
- solar energy
give an example of non-renewable energy
fossil fuels
examples are: coal/oil/gas
what are advantages of generating power using gas rather than coal
- flexible generation: gas power stations have short start-up times so can be switched off more easily and regularly
- lower emissions of carbon dioxide
state 2 disadvantages of renewable energy resources used to generate power
- output often determined by external factors, like wind speed, so supply is not certain
- generating power through other means is often more efficient and economically beneficial
explain environmental impacts of burning fossil fuels
- carbon dioxide contributes to the greenhouse effect, and causes global warming
- sulphur dioxide leads to acid rain, which can damage buildings and crops
state 3 advantages of fossil fuels as an energy resource
- reliable: not dependent on external factors so can generate power at any time
- can produce large amounts of energy for a given quantity
- still relatively abundant, so cost efficient
state 3 advantages of nuclear power
- very large amounts of energy for relatively small quantities of fuel
- doesn’t release greenhouse gases so it doesn’t contribute to climate change
- low fuel costs
state 3 disadvantages of nuclear power
- produces nuclear waste which is harmful to humans and must be safely stored for centuries
- non-renewable energy source
- risk of nuclear accidents, which have fatal consequences on humans and the environment
how does hydroelectric power produce energy
- rainwater collects behind a dam
- when this water is released it is used to turn a turbine
- this turbine turns a generator which produces electricity
what are some disadvantages of using biofuels
- when plants are burned or decay they release CO2
- in order to grow biofuels, you need to destroy land which causes issues like destroying natural habitats, or releasing CO2
- growing biofuels reducing land available growing for food
what are advantages of tidal energy sources
- they do not produce greenhouse gases
- quite reliable as tides always happen twice a day
- cheap to run as tides are natural and are free
disadvantages of hydroelectric power
the dam may cause flooding
can cost a lot to install the required infrastructure
advantages of solar panels
- they don’t cause harm to the environment
- they are renewable
- they can be used in remote areas where other types of electricity is less available
examples of a social factor which may act as a deterrent for certain types of energy production
- visual pollution
- sound pollution
disadvantage of wind farms
- visual pollution
- sound pollution
