Energy Flashcards
What is the equation for kinetic energy?
kinetic energy = 1/2 x mass x speed^2
What is the equation for elastic potential energy?
Elastic potential energy (J) = 0.5 x spring constant (N/m) x (extension (m))^2
What is the equation for gravitational potential energy?
gravitational potential energy = mass x gravitational field strength x height
What is the ‘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
What are the units for specific heat capacity?
Joules per kilogram per degree Celsius (J/kg °C)
What is the definition of ‘power’?
The rate at which energy is transferred or the rate at which work is done
State two equations for power. Give SI units for all quantities involved.
power = energy transferred/time
power = work done/time
Energy (J), Work Done (J), Time (s)
What is the unit of power?
Watt (W)
Describe the energy transfers for a bungee jumper.
● When falling, the GPE is converted to KE of jumper
● As the cord tightens, KE is converted and stored as Elastic Potential Energy (EPE)
● At lowest point, the jumper’s 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)², as KE decreases, so does velocity.
State 4 different stores of energy.
- Kinetic Energy
- Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Energy
Give examples of kinetic energy stores
Compressed springs and inflated balloons
Give examples of gravitational potential energy stores
Aeroplanes and kites
Give examples of elastic potential energy
A bent diving board and archers stretched bow
Give examples of chemical energy stores
food, fuel and batteries
What is the law of energy conservation?
Energy cannot be created or destroyed
State any 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 waste energy
What are two equations to calculate efficiency?
=Useful Output Energy Transfer/Total Input Energy Transfer
=Useful Power Output/Total Power Output
How can the efficiency of a system be increased?
- Reducing waste output (by lubrication, thermal insulation etc.)
- Recycling waste output (eg. recycling thermal waste energy as input energy)
What is 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?
● The thickness of the walls
● The thermal conductivity of the walls
What are three methods of reducing heat loss in a building?
- Double glazing
- Loft and wall insulation
- Thicker walls
How can the efficiency of 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 improved?
Insulting 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.
What are four examples of renewable energy resources?
- Wind Energy
- Hydro-Electricity
- Tidal Energy
- Solar Energy
What is an example of non-renewable energy resource?
Fossil fuels (for example coal, oil and 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
What are two disadvantages of using renewable energy resources to generate power?
● Output often determined by external factors (like wind speed), 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 the greenhouse effect, and causes global warming
● Sulphur Dioxide leads to acid rain, which can damage buildings and crops
What are 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
What are 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
What are 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
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 leads to problems because:
● The land could have been natural habitats
● Destroying land may involve burning plants growing on it, which would release CO2
● Growing biofuels reduces the land available for growing food
What are the advantages of tidal energy sources?
● They do not produce greenhouse gases
● They are quite reliable, as tides happen twice a day
● They are cheap to run as tides are natural, and so are free
What are the disadvantages of hydroelectric power?
● The dam may cause flooding
● It can cost a lot to install the required infrastructure
What are some advantages of solar panels?
● They don’t cause harm to the environment
● They are a renewable resource
● They can be used in remote areas where other types of energy are less accessible
What are examples of social factors which may act as a deterrent for certain types of energy production?
● Visual Pollution
● Sound Pollution
(both of these are disadvantages of wind farms)
What are thermal conductors?
Materials with a low specific heat capacity so heat up and cool down quickly
What are thermal insulators?
Materials with a high specific heat capacity so heat up and cool down slowly
How do you improve energy?
Reduce the amount of energy that a device wastes or dissipates to the surroundings
What ways could you improve efficiency?
1) Lubricate mechanical devices to reduce the friction between moving parts of the machine
2) Insulate heating devices to reduce the dissipation of thermal energy to the surroundings
What is conduction?
When heat is transferred through a material due to vibrating particles colliding and transferring energy from one particle to another
Image: Conduction
What is convection?
When heat is transferred through a moving liquid or gas due to differences in densities
What is radiation?
When heat is transferred from a hot object due to the object emitting infrared (heat) radiation
