Topic 1: Energy Flashcards
1.1
Energy Changes in a System
What is the equation for kinetic energy? Give SI units for all quantities involved.
- 1/2 x m x v²
- 1/2 x mass x velocity²
- Energy (J), Mass (kg), Velocity (m/s)
What is the equation for elastic potential energy?
Give SI units for all quantities involved.
- 1/2 x k x x²
- 1/2 x spring constant x extension²
- Energy (J), Spring constant (N/m), Extension (m)
What is the equation for gravity potential energy?
Give SI units for all quantities involved.
- mgh
- Mass x Gravitational Field Strength x Height
- Energy (J), Mass (kg), Gravitational Field Strength (N/kg), Height (m)
Define the ‘Specific Heat Capacity’ of a substance.
The amount of energy needed to raise the temperature of 1 kg of a substance by 1ºC.
State the units for Specific Heat Capacity
- J/ºC/kg
- 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 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)
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 transferred is the same but the time taken is less (P=E/t)
Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position. Ignore air resistance.
- Upwards: KE is converted to GPE
- Peak: Maximum GPE, zero KE
- Downwards: GPE is converted to KE
KE (Kinetic Energy), GPE (Gravitational Potential Energy)
Describe the energy transfers for a bungee jumper.
- When falling, the gravitational potential energy is converted to kinetic energy of the jumper
- As the cord tightens, kinetic energy is converted and stored as elastic potential energy
- At lowest point, the jumper’s initial gravitational potential energy equals the elastic potential energy 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 kinetic energy is proportional to (velocity)², as kinetic energy decreases, so does velocity
Give examples of chemical energy stores.
- Food
- Fuel (e.g. wood, coal, petrol)
- Batteries
State 4 different stores of energy.
- Kinetic Energy
- Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Energy
1.2
Conservation and Dissipation of Energy
State the law of energy conservation.
Energy cannot be created or destroyed (it can only be transferred into different forms).
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
State 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 (e.g. 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?
- The thickness of the walls
- The 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? (Higher)
Lubricate any moving parts to reduce the friction and therefore energy loss due to heating.
How can the efficiency of a radiator be improved? (Higher)
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? (Higher)
By placing a lid on the pan to reduce the heat loss from the top.
1.3
National and Global Energy Resources
What is a renewable energy source?
An energy source which can be replenished as it is being used up.
Give four examples of renewable energy resources.
- Wind Energy
- Hydro-Electricity
- Tidal Energy
- Solar Energy
Give an example of a 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
State two disadvantages of using renewable energy resource 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 furls.
- Carbon Dioxide contributes to the 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 & 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 produces 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
Give 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)
