energy Flashcards
what is the equation for kinetic energy?
kinetic energy (J) = 0.5 x mass (kg) x velocity² (m/s)
what is the equation for elastic potential energy?
elastic potential energy (J) = 0.5 x spring constant (N/m) x extension² (m)
what is the equation for gravitational potential energy?
gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
define ‘specific heat capacity’ of a substance
amount of energy needed to raise the temperature of 1kg of a substance by 1°C
what are the units for specific heat capacity?
J/°C/kg
what is the definition of ‘power’?
rate at which energy is transferred (or rate at which work is done)
give two equations for power
power = energy transferred (J) / time (s)
power = work done (J) / time (s)
what is the unit for power?
watts (W)
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 as the energy transferred is the same but time taken is less (P=E/t)
describe the energy changes involved when a ball is thrown upwards + then returns to its 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, GPE is converted to KE of jumper
-as cord tightens, KE is converted + stored as EPE
-at lowest point, jumper’s initial GPE = EPE stored in cord
explain why a bungee jumper slows down once the cord begins to stretch
-KE decreases since it’s converted to EPE
-since KE is proportional to velocity², as KE decreases so does velocity
give examples of chemical energy stores
-food
-fuel (e.g. wood / coal / petrol)
-batteries
state four different stores of energy
-kinetic energy
-gravitational potential energy
-elastic potential energy
-chemical energy
state the law of energy conservation
energy cannot be created or destroyed only transferred
state any changes in the total energy of a ball that is kicked
total energy of system remains constant due to conservation of energy
what is waste energy?
energy that isn’t 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 + heat energy
-light is a useful energy form, heat is waste energy
state two equations to calculate efficiency
efficiency = useful output energy / total input energy
efficiency = useful power output / total power input
how can the efficiency of a system be increased?
-reducing waste output (by lubrication / thermal insulation etc.)
-recycling waste output (e.g. recycling thermal waste energy as input energy)
state the consequences 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 that single-glazed windows?
lower meaning less energy transfers through them
what key factors affect the rate of cooling of a building?
thickness and 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 reduce 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 heat loss from the top
what is a renewable energy resource?
an energy source which can be replenished as it is being used up
give four examples of renewable energy resources
-wind energy
-hydroelectricity
-tidal energy
-solar energy
give an example of a non-renewable energy resource
fossil fuels (e.g. coal / oil / gas)
what are the advantages of generating power using gas rather than coal?
-flexible generation: gas power stations have short start-up times so can be switched on/off more readily
-lower emissions of carbon dioxide
state two disadvantages of using renewable energy resources to generate power
-output often determined by external factors so supply is uncertain
-generating power through other means is often more efficient and economically beneficial
explain the environmental impacts of burning fossil fuels
-carbon dioxide contributes to greenhouse effect and causes global warming
-sulphur dioxide leads to acid rain which can damage buildings and crops
state three advantages of fossil fuels as an energy resource
-reliable: not dependent on external factors so can generate power anytime
-can produce large amounts of energy for a given quantity
-still relatively abundant so cost-effective
state three advantages of nuclear power
-very large amounts of energy for relatively small quantities of fuel
-doesn’t release greenhouse gases and so doesn’t contribute to climate change
-low fuel costs
state three disadvantages of nuclear power
-produces nuclear waste which is harmful to humans and must be stored
-non-renewable energy source
-risk of nuclear accidents which have fatal consequences on humans and environment
how does hydroelectric power produce energy?
-rainwater collects behind a dam
-when water is released it is used to turn a turbine
-this turns a generator which produces electricity
what are some disadvantages of using biofuels?
-when plants are burned / decay they release CO2
-to grow biofuels you need to destroy land which could be natural habitats or release CO2
-growing biofuels reduces land available for growing food
what are the advantages of tidal energy sources?
-don’t produce greenhouse gases
-quite reliable as tides happen twice daily
-cheap to run as tides are natural and free
what are the disadvantages of hydroelectric power?
-dam may cause flooding
-cost a lot to install required infrastructure
what are some advantages of solar panels?
-they don’t cause harm to the environment
-renewable resource
-used in remote areas where other types of energy are less accessible
give examples of social factors which may act as a deterrent for certain types of energy production
-visual pollution
-sound pollution
(both disadvantages of wind farms)
state the equation used to calculate the temperature change when a substance is heated
change in thermal energy (J) = mass (kg) x specific heat capacity (J/°C/kg) x temperature change (°C)
if the power of the heater being used isn’t given, how do you calculate it?
connect it in parallel with a voltmeter and in series with an ammeter and then use P = IV
why do the metal blocks used in the experiment have two holes in them?
one is for the heater and one is for the thermometer
what can be done to improve the reading given by the thermometer?
add a few drops of water in the hole with the thermometer to improve the thermal contact and ensure even heating
what reading do you record during the experiment and how frequently?
you record the temperature value every 10 minutes from when the heater is inserted and switched on
what graph do you plot with the data?
temperature against work done by the heater
how do you calculate the work done by the heater?
energy = power of heater x time
where energy is equivalent to work done
once the block has initially warmed up, describe the graph of temperature against work done by the heater that should be obtained
it should be a linear relationship and so should produce a straight line
if you start timing from when you switch on the heater, why may the graph not initially be linear?
there will initially be some thermal inertia whilst the block and heater warm up
what does the gradient of the graph represent?
the inverse of the heat capacity for the metal block
how do you obtain the specific heat capacity for the metal you are measuring?
divide the inverse of the gradient by the mass of the metal block used
what is the difference between heat capacity and specific heat capacity?
specific heat capacity is the heat capacity measured for a mass of 1kg
why should you wrap insulation around the outside of the metal block?
to reduce the heat loss to the environment and ensure the temperature reading is as accurate as possible
what safety precautions should be taken when carrying out this experiment?
-avoid touching metal
-use a heatproof mat
-avoid spilling water near power supply
