Energy production Flashcards
What is the difference between primary and secondary energy?
Primary - energy that is found in nature and has not been processed or exploited.
Secondary - energy that is produced from primary energy, eg. electricity.
What is specific energy?
EsubS = Q/m = the amount of energy that can be extracted from a unit mass of fuel, Jkg⁻¹
What is energy density?
EsubD = Q/V = the amount of energy that can be extracted from a unit volume of fuel Jm⁻³
What are non-renewable energy sources?
What are renewable energy sources?
- Finite sources that are depleted faster than they are produced.
- Sources which cannot be used up
What are fossil fuels?
How are they used to produce energy?
- The are decomposed plant and animal matter broken down by bacteria and exposed to high pressure.
- At a power plant, burning coal and oil boils water in a boiler
- Pressurised steam forces a turbine to turn, which turns a generator, creating electricity
- Cold water condenses the steam into liquid before the cycle repeats.
What is a sankey diagram?
A block arrow diagram showing the flow of energy, and energy lost in different forms.
What is efficiency?
What is power?
e = useful power/input power power = energy/time (Js⁻¹)
What are the advantages and disadvantages of fossil fuels? [6]
- Relatively cheap
- High energy density
- Distribution network is in place.
- Non-renewable
- Pollutes the environment
- Contributes to greenhouse effect.
What are the following from a nuclear reactor: critical mass moderator heat exchanger control rods
- The critical mass is the minimum mass required for a a chain reaction to occur - the amount of uranium-235 present.
- A material surrounding fuel rods that slows down neutrons through collisions and heats as a result, pressurised water or graphite.
- A separate material that extracts heat from the moderator, eg. cold water that circulates in pipes and is turned to steam.
- Rods which absorb neutrons lowered in the moderators to control the rate of reaction.
What are the advantages and disadvantages of nuclear power? [6]
- High power output
- Large reserves of nuclear fuels
- No greenhouse gases produced
- Radioactive waste hard to dispose of
- Public health hazard if accidents happen
- Difficulty of uranium mining.
What are two ways of using solar power?
- Solar panels where the sun is used to directly heat water, which flows in pipes below a blackened surface.
- Photovoltaic cells convert sunlight to electricity, can be used in remote areas.
What are the advantages and disadvantages of solar power? [7]
- Free to run
- Inexhaustible energy
- Non-polluting
- Works only during the day
- Affected by cloudy area
- Low power output
- High initial cost
How do hydroelectric power plants work?
What is a pumped storage system?
How can you calculate the power output?
- Water from a reservoir falls through a vertical height, potential energy is converted to kinetic energy, which is used to drive turbines.
- When there is low demand, water is pumped back up to the reservoir.
P = mgh/Δt = ρQgh
What are the advantages and disadvantages of hydroelectric power?
- Easy to regulate supply to fit demand
- Inexhaustible source
- Non-polluting
- Very dependent on location
- Drastically changes the environment
- High initial cost
How can you calculate the theoretical maximum power output of a wind turbine?
Imagine a cylinder of air passing through the blades, of length vΔt, density ρ, area A, moving at a speed v. By working out the kinetic energy of the cylinder, and dividing by Δt, P = 1/2 ρAv³
How does conduction work? [2]
- The electrons at high temperature have high average KE, and collide with neighbouring molecules, transferring KE.
- When there are strong bonds, the vibration of molecules causes bonds to stretch, & neighbouring molecules to vibrate as well.
How does convection work?
Hot fluids expand and rise, transferring thermal energy to another area. Cold fluids take the place of the hot fluids and the cycle repeats, creating a convection current.
How can you work out the power radiated by a hot body?
P = eσAT⁴ e = emissivity (effectiveness at radiating between 0-1) σ = Stefan-Boltzmann constant A = surface area (m²) T = surface temperature (K)
What is Wien’s displacement law?
The modal wavelength of radiation emitted by a body, λmax = 2.9 x 10⁻³ / T (K)
In data book
What is intensity?
How can you work out the intensity of radiation from the sun? (solar constant)
It is the power of radiation received per unit area. I = P/A
I = P/4πr² where r is the distance between the earth and sun.
What is albedo?
The ratio of power of radiation scattered from a body to power incident.
α = total scattered power/total incident power
How can you work out the total intensity incident on the earth during the day?
Imagine a disc the radius of the earth, r.
P = Sπr²
Multiply by albedo to get reflection or absorption.
P = αSπr² , P = (1 - α)Sπr²
To find intensity across the whole sphere, divide by the area 4πr²
What is one way to calculate the energy balance of the earth?
Equate the average radiation intensity incident (I = (1-a)S/4) and the intensity radiated out using (P = eσAT⁴). Assume earth is a black body.
Find T.
How does the greenhouse effect work?
What are some greenhouse gases, and sources?
Infrared radiation, emitted by the earth’s surface is absorbed by greenhouse gases, and partially re-radiated towards the surface.
- Water vapour - evaporation from oceans, CO2 - burning fossil fuels, methane - farm animals, nitrous oxide - fertilisers, forests.
How does the greenhouse effect work through photon absorption?
Infrared photons with the right amount of energy are absorbed by molecules, which are excited, and then emit photons in all directions, some towards earth.
What is a black body?
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