Topic 8 - Energy Production

Emissivity

The ratio of actual power emitted to power emitted by a black body

Albedo

The ratio of reflected intensity/power to incoming intensity/power.

thermal radiation

emission of (infrared) electromagnetic/infrared energy/waves/radiation

Mechanism of infrared absorption of greenhouse gases

Molecules of greenhouse gases have energy levels and their energy level differences correspond to infrared photon energy → molecules are good at absorbing and re-emits back to Earth’s surface

Without greenhouse gases, less infrared is absorbed and trapped, so less infrared is re-radiated to Earth, hence the Earth’s surface is less heated up and its surface temperature decreases

Why fuel enrichment is necessary for the fuel used in a commercial nuclear reactor

• U-235 is more fissionable than U-238

• Naturally occurring uranium ore contains more U-238 atoms than U-235 atoms

• In fuel enrichment, U-238 is removed, increasing the concentration of U-235

Outline, with reference to the speed of the neutrons, the role of the moderator in a nuclear reactor

• Neutrons emitted from uranium at high speed

• High-speed neutrons do not cause fission

• Neutrons collide with moderator atoms

• Therefore lose energy/speed before re-entering fuel rods

Distinguish between a solar heating panel and a photovoltaic cell

• Solar heating panel convert radiation energy of the Sun directly into thermal/heat energy

• Photovoltaic cells convert into electrical energy

Outline, with reference to energy changes, the operation of a pumped storage hydroelectric system

PE of water is converted to KE of moving water/turbine to electrical energy in generator/turbine/dynamo

Water is pumped back up when the demand for and prices of electricity is low, then water is released and hydroelectricity is generated when the demand for and prices of electricity is high → make a profit

Mechanism of wind turbines

• kinetic energy of wind transferred to (rotational) kinetic energy of turbine/blades

• kinetic energy is changed to electrical energy in a generator/dynamo

• (Generator/dynamo must be mentioned)

Mechanism of nuclear power production

• KE of fission fragments → nuclear energy → thermal energy of the coolant/water/steam

• Thermal energy → KE or (rotating) magnets/coils/turbines/generators → electrical energy

Mechanism of coal-fired/fossil fuel power production

• Burning gas

• Internal energy/KE of steam/particles transfers to KE of turbine, which transfers to KE of generator/dynamo producing electrical energy

Wind Turbines Advantages

• wind is renewable so no resources used up

• wind is free

• no chemical pollution

• no carbon dioxide emission

• does not contribute to greenhouse effect

• Is “scalable” i.e. many sizes of turbine possible

Wind Turbines Disadvantages

• expensive initial cost

• large land area needed

• wind not constant

• effect on movement of birds

• aesthetically unpleasant

• noise pollution

• high maintenance costs

• best locations far from population centres

• low energy density

Nuclear power production Advantages

• Nuclear power does not produce carbon dioxide → does not add to global warming

• Energy density of U-235 (fuel) is very high/small mass is required → fuel likely to last a long time/easier to transport

Nuclear power production Disadvantages

• Accidents are potentially catastrophic → leading to widespread cancers

• Allows the development of nuclear weapons like dirty bombs

• Waste products of U-235 are radioactive → no safe method of disposal

• Power plant is more expensive because of eg. safety measures, decommissioning, etc.

Coal-fired/fossil fuel power production Advantages

• No radioactive waste

• No radiation risks to users

• Easier to install/lower cost of decommissioning

• Safer transportation and storage

• Simpler technology

• Cannot be used for military purposes

• Fossil fuels can be found/extracted more easily

• No chance of meltdown/catastrophic accident/Chernobyl

• Plentiful supplied at present

• Pre-existing infrastructure

• Easily portable, easily mined

Coal-fired/fossil fuel power production Disadvantages

• Contributes to greenhouse effect

• Non renewable → will run out