Topic 8: Energy Production Flashcards

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1
Q

Define The Law of Conservation of Energy

A

“Energy cannot be created or destroyed, only changed from one form to another.” (To transfer energy work is done, with the exception of thermal energy transfer)

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2
Q

Define fuels

A

Sources of energy.

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3
Q

Define energy density

A

The energy liberated per unit volume of fuel consumed. (Jm-3 or MJm-3)

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4
Q

Define specific energy

A

The energy liberated per unit mass of fuel consumed. (Jkg-1 or MJkg-1)

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5
Q

Define The Second Law of Thermodynamics

A

It is not possible to convert heat completely into work as some heat is always lost to the surroundings (known as degraded energy).

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6
Q

Define primary sources of energy

A

Sources that have not been transformed or converted before use eg. directly burning coal to heat something.

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7
Q

Define secondary sources of energy

A

Sources that result from the transformation of a primary source eg. electrical energy generated by coal-fired power stations

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8
Q

Define renewable energy

A

Energy that cannot be used up.

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9
Q

Define non-renewable energy

A

Energy that can be used up because they are used at a greater rate than they are produced.

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10
Q

Give the advantages and disadvantages of fossil fuel usage

A

Advantages:- Very high energy density- Easy to transport - Cheap- Power stations can be built anywhereDisadvantages:- Combustion products are harmful to the environment (eg. acid rain and greenhouse gases)- Fuel extraction can damage the environment- Non-renewable energy source- Power stations need large amounts of fuel

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11
Q

Give the efficiency of fossil fuels —> electrical energy(coal, oil and natural gas)

A

Coal (35%)Oil (38%)Natural gas (45%)

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12
Q

Define degraded energy

A

The heat energy that is lost to the surroundings.

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13
Q

How is electrical energy generated? (General process)

A

The flow of a fluid (eg. moving water, pressurised steam, wind) is used to spin a turbine which then spins a generator. The magnets spinning past copper coils in the generator produces electrical energy.

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14
Q

Define a kilowatt-hour

A

The amount of energy used by a 1kW device in one hour.

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15
Q

How are fossil fuels used to generate electricity?

A

Fossil fuels are burnt in power stations and the thermal energy released is used to boil water and create steam. This steam is used to spin turbines which are attached to generators that produce electricity.

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16
Q

How do nuclear power stations generate electricity?

A

Naturally occurring uranium-238 is enriched to uranium-235.A neutron source is used to initiate nuclear fission. The power stations use the energy released from nuclear fission to heat water, create steam and spin a turbine/generator to produce electricity.

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17
Q

What are the three key components of a nuclear reactor?

A

1) The moderator (eg. heavy water)This makes fission happen by slowing down the high-energy neutrons so that they are more likely to collide with the uranium-235. 2) Control rodsThe control rods control the rate of fission by absorbing neutrons. By lowering them into or out of the reactor core the fission reaction can be controlled. 3) Heat exchangerThe water heated from the fission reaction enters the heat exchanger and its thermal energy is transferred to a separate circuit containing cold water to convert it into steam to drive turbines.

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18
Q

Give the efficiency of nuclear power

A

30%

19
Q

Give the advantages and disadvantages of nuclear power

A

Advantages:- High specific energy (a million times more coal is needed to produce the same amount of energy)- No greenhouse gases produced- Large reserve of uraniumDisadvantages:- Radioactive waste is produced- High risk - Non-renewable source of energy (but large reserves of uranium so will last a long time)

20
Q

Give the safety issues with nuclear power

A
  • Uranium mining is hazardous.- If the reactor core (the fuel) is not constantly cooled then thermal meltdown can occur which will spread radioactive material.- There is radioactive waste produced which must be stored for millions of years.- Transportation of uranium and radioactive waste is hazardous.- The by-products of nuclear power (eg. plutonium-239) can be used to make nuclear weapons.
21
Q

Why is nuclear fission used to generate electricity, not nuclear fusion?

A

Nuclear fusion occurs naturally in the stars but is too hard to create artificially. Very high temperatures and pressures are required for it to occur so the nuclei can overcome electrostatic repulsion and combine.

22
Q

What does the formula P=½Apv³ give?

A

The theoretical maximum power available in the wind. In reality, only 30% will be converted to electrical energy because not all kinetic energy in the air can be converted as some air must pass through unused to turn the rotors and there are thermal energy losses due to friction in the turbine/generator.

23
Q

Give the advantages and disadvantages of wind power

A

Advantages:- Clean (no greenhouse gases produced)- Renewable source of energy- FreeDisadvantages:- Unreliable (amount of wind changes daily)- Low energy density so lots of wind turbines are needed- Need to be built far from population centres

24
Q

Give the efficiency of wind power

A

30%

25
Q

What is the original source of wind power?

A

The Sun.Solar energy from the sun gives the land and atmosphere thermal energy which creates wind.

26
Q

Give the formula for efficiency

A

Useful power out/total power in x 100

27
Q

What are the three ways water can be stored for hydroelectric power?

A

1) By using a dam2) Capturing water at high tide and releasing it at low tide3) By pumping water from a low to a high reservoir (pumped storage)

28
Q

Give the efficiency of hydroelectric power

A

90%

29
Q

What are the energy losses of hydroelectric power?

A
  • Friction losses due to the turbulence of water in the penstock- Friction in the turbines and generator- Electrical heating losses due to resistance of wiring
30
Q

Give the advantages and disadvantages of hydroelectric power

A

Advantages:- Clean (no greenhouse gases produced)- Renewable- FreeDisadvantages:- Only available in areas with large bodies of water- Building dams involves large areas of land being covered by water

31
Q

What are the two uses of the Sun’s radiation in terms of solar power?

A

Solar heating panel (converts solar energy -> thermal energy and is used to heat water in houses)Photovoltaic cell (used to produce small amounts of electrical energy)

32
Q

Give the advantages and disadvantages of solar power

A

Advantages:- Clean (no greenhouse gases produced)- Renewable- FreeDisadvantages:- Only available during the day (when electrical needs are low)- Unreliable (depends on cloud cover)- Low energy density (large solar panels are needed)- Sunlight varies depending on the season

33
Q

Give the formula for the area of solar panels

A

Area = power input/power per m2

34
Q

Give the formula and units for specific energy

A

Specific energy = Ep or Ek/massUnits Jkg-1

35
Q

W -> MW -> GW

A

W -> MW ÷ 10⁶MW -> GW ÷ 1000

36
Q

What is conduction?

A

The transfer of thermal energy without any overall movement of the molecules/atoms that make up the substance. It is more effective in solids (particularly metals). It can occur in gases and liquids but to a much lesser extent because of the weaker interatomic/molecular bonds and increasing distance between atoms/molecules.

37
Q

What is convection? And, how are convection currents formed?

A

The transfer of thermal energy by bulk movement of the atoms/molecules that make up the substance. It only takes place in liquids and gases. The heated region of the fluid expands (molecules move further apart). This region has a lower density than surrounding fluid so rises. A colder, denser region of fluid fills the space left behind, is heated and the process repeats. This is called a convection current.

38
Q

What the model used for thermal radiation?

A

A black-body. It is a “perfect” emitter/absorber of radiation. The amount it emits/absorbs does not depend on the nature of its surface but on its temperature.

39
Q

Define emissivity.

A

The power radiated by an object per unit area divided by the power radiated per unit area by a black body at the same temperature.

40
Q

What is the global annual mean albedo for Earth?

A

0.3 (therefore this means 30% of solar radiation incident on Earth is reflected back into space and 70% is absorbed).

41
Q

Define the solar constant.

A

The amount of solar energy that falls per second on an area of 1m² above the Earth’s atmosphere.

42
Q

Give examples of greenhouse gases.

A

Methane (CH₄)Water vapour (H₂O)Carbon dioxide (CO₂)Nitrous oxide (N₂O)

43
Q

What do greenhouse gases do?

A

They absorb the infra-red radiation emitted by the Earth’s surface and re-emit it in all directions. Some of this will be reabsorbed by the surface causing the Earth’s average temperature to rise. *Note: greenhouse gases are able to absorb the infra-red radiation because the frequency of this matches the resonant frequency at which the greenhouse gases vibrate. This is a phenomenon called resonance.

44
Q

Why do polar ice caps have the highest albedo?

A

Because they have multiple layers which reflect radiation whereas a body of water only has one.