Energy production

Question 1

What is the difference between primary and secondary energy?

Answer 1

Primary - energy that is found in nature and has not been processed or exploited.
Secondary - energy that is produced from primary energy, eg. electricity.

Question 2

What is specific energy?

Answer 2

EsubS = Q/m = the amount of energy that can be extracted from a unit mass of fuel, Jkg⁻¹

Question 3

What is energy density?

Answer 3

EsubD = Q/V = the amount of energy that can be extracted from a unit volume of fuel Jm⁻³

Question 4

What are non-renewable energy sources?

What are renewable energy sources?

Answer 4

• Finite sources that are depleted faster than they are produced.
• Sources which cannot be used up

Question 5

What are fossil fuels?

How are they used to produce energy?

Answer 5

• 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.

Question 6

What is a sankey diagram?

Answer 6

A block arrow diagram showing the flow of energy, and energy lost in different forms.

Question 7

What is efficiency?

What is power?

Answer 7

e = useful power/input power
power = energy/time (Js⁻¹)

Question 8

What are the advantages and disadvantages of fossil fuels? [6]

Answer 8

• Relatively cheap
• High energy density
• Distribution network is in place.
• Non-renewable
• Pollutes the environment
• Contributes to greenhouse effect.

Question 9

What are the following from a nuclear reactor:
critical mass
moderator
heat exchanger
control rods

Answer 9

• 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.

Question 10

What are the advantages and disadvantages of nuclear power? [6]

Answer 10

• 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.

Question 11

What are two ways of using solar power?

Answer 11

• 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.

Question 12

What are the advantages and disadvantages of solar power? [7]

Answer 12

• Free to run
• Inexhaustible energy
• Non-polluting
• Works only during the day
• Affected by cloudy area
• Low power output
• High initial cost

Question 13

How do hydroelectric power plants work?
What is a pumped storage system?
How can you calculate the power output?

Answer 13

• 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

Question 14

What are the advantages and disadvantages of hydroelectric power?

Answer 14

• Easy to regulate supply to fit demand
• Inexhaustible source
• Non-polluting
• Very dependent on location
• Drastically changes the environment
• High initial cost

Question 15

How can you calculate the theoretical maximum power output of a wind turbine?

Answer 15

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

Question 16

How does conduction work? [2]

Answer 16

• 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.

Question 17

How does convection work?

Answer 17

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.

Question 18

How can you work out the power radiated by a hot body?

Answer 18

P = eσAT⁴
e = emissivity (effectiveness at radiating between 0-1)
σ = Stefan-Boltzmann constant
A = surface area (m²)
T = surface temperature (K)

Question 19

What is Wien’s displacement law?

Answer 19

The modal wavelength of radiation emitted by a body, λmax = 2.9 x 10⁻³ / T (K)
In data book

Question 20

What is intensity?

How can you work out the intensity of radiation from the sun? (solar constant)

Answer 20

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.

Question 21

What is albedo?

Answer 21

The ratio of power of radiation scattered from a body to power incident.
α = total scattered power/total incident power

Question 22

How can you work out the total intensity incident on the earth during the day?

Answer 22

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

Question 23

What is one way to calculate the energy balance of the earth?

Answer 23

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.

Question 24

How does the greenhouse effect work?

What are some greenhouse gases, and sources?

Answer 24

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.

Question 25

How does the greenhouse effect work through photon absorption?

Answer 25

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.

Question 26

What is a black body?

Answer 26

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