IB Physics Topic 8 Energy production

Degraded energy

- Energy that is transferred from the system to the surrounding that is no longer available to perform useful work.

Sankey diagrams

- shows the energy conversions that are taking place in the system.
- The width of the arrow represents the power or energy involved at a given stage.
- Degraded energy is shown with an arrow up or down.

Electrical power production

1) A fuel is used to release thermal energy.
2) The thermal energy is used to boil water to make steam.
3) The steam is used to turn turbines and the motion of the turbines is used to generate electrical energy.

Law of conservation of energy

- energy is neither created nor destroyed, it just changes form.

Renewable sources

- Sources of energy that cannot be used up.
- Examples: hydroelectric, photovoltaic cells, active solar heaters, wind, biofuels.

Non-renewable sources

- Sources of energy that can be used up and eventually run out.
- Examples: coal, oil, natural gas, nuclear.

Sources not involving the sun

1) Gravitational energy of the Sun and the Moon.
2) Nuclear energy stored within atoms.
3) The Earth's internal heat energy

Energy density

- The energy liberated per unit mass of fuel consumed.

Fossil fuel

- The dead matters that have accumulated over millions of years are converted into this by exposure to very high temp. and pressure that exist beneath the Earth's surface.

Energy transformation of fossil fuel power production

1) solar energy => 2) chemical energy in plants through photosynthesis => 3) chemical energy in fossil fuels through compression => 4) thermal energy through burning => 5) KE of steam => 6) KE of turbines => 7) electrical energy.

Advantages of fossil fuels

- Very high 'energy density'
- Easy to transport
- Cheap
- Can be built anywhere with good transport links
- Can be used directly in the home to provide heating.

Disadvantages of fossil fuels

- Can cause pollution/acid rain; damage the environment.
- Can produce greenhouse gases.
- Nonrenewable
- Coal-fired power stations need large amounts of fuel.

Nuclear power

- Energy is created through fission reaction of uranium-235.

Critical mass

- As the size of a block of fuel increases so do the chances of a neutron causing a further reaction => can set up the stage for a chain reaction to occur.
- The mass for which the chain reaction would occur.

Energy transformation of Nuclear power

1) nuclear energy of core => 2) thermal energy of coolant (some thermal energy lost to environment) => 3) KE of steam turbine => 4) electrical energy.

Moderator

slows down the neutrons and the nuclei to allow further reactions to take place.

Control rods

where it can readily absorb neutrons.
- Can be introduced or removed from the reaction chamber in order to control the chain reaction.

Heat exchanger

- part of the nuclear power plant where it allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment.
- heat is transferred from the fluid circuit through the reactor core to a circuit through the turbine.

Advantages of nuclear power

- Extremely high 'energy density'
- Reserves of uranium is large compared to oil.
-no greenhouse gas emissions

Disadvantages of nuclear power

- The process produces radioactive nuclear waste.
- Larger possible risk if anything goes wrong.
- Nonrenewable

Enrichment

- Process by which the percent composition of uranium-235 in uranium is increased to make nuclear fission more likely.

Reprocessing

- Process to treat used fuel waste from nuclear reactors to recover uranium and plutonium and to deal with other waste products.
- Fast breeder reactor is often used to create plutonium-239.

Plutonium-239

- Substance also capable of sustaining fission reactions in addition to uranium-235.
- Created through reacting uranium-238 through a combination nucleus capture and ß-decay:
1) ₉₂²³⁸U + ₀¹n -> ₉₂²³⁹U
2) ₉₂²³⁹U ->₉₃²³⁹Np + ₋₁⁰ß + ṽ
3) ₉₃²³⁹Np ->₉₄²³⁹Pu + ₋₁⁰ß + ṽ

Thermal meltdown

- A possible risk of nuclear reactor caused by an uncontrolled nuclear fission (would happen if control rods were removed).

Nuclear weapons

- Created through uncontrolled nuclear fission.
- Can cause mass destruction.

Fusion reactors

- Theoretical potential of significant power generation without many problems associated with current nuclear fission reactors.
- Produce energy in process of hydrogen atoms joining together to form helium, releasing heat
Problems: maintaining and confining plasma at high temp. and density for fusion to take place.

Photovoltaic cell

- One device that converts light energy to electrical energy.
- Uses a piece of semiconductor (photocell) to convert portion of the radiated energy directly into a potential difference.
- Cannot produce a great amount of energy.

Active solar heater

- One device that converts solar energy into thermal energy.
- Designed to capture as much thermal energy as possible to produce hot water.
- Can be used in the home

Solar constant

- The amount of solar energy that falls per second on an area of 1 m^2 above the Earth's atmosphere that is at right angles to the Sun's rays (not the power that arrives on Earth's surface. Most are reflected or absorbed).
- Average value: 1400W m^(-2)

Disadvantages of solar power

- Can only be utilized during the day.
- Unreliable (cloudy days).
- Low energy density.

Intensity

- Power received per unit area.
- I = P/(4πr^2) (inversely proportional to the square of distance from the point source to the receiver = inverse square law).

Albedo

- The fraction of radiation received by a surface that is reflected back into space.
- Varies daily depending on season and place (Ocean has low value, snow has high).
- Global mean in 30% on Earth.

Energy transformation of hydroelectric power

1) gravitational PE of water => 2) KE of water => 3) KE of turbines => 4) electrical energy.

Disadvantages of hydroelectric power

- Can only be utilized in particular areas.
- Construction of dam will involve land being buried under water.

Energy transformations of wind power

1) Solar energy => 2) KE of wind created due to heating of Earth => 3) KE of turbine => 4) electric energy.

Mathematics of wind power

- KE = (1/2)A p v^3 (derived from equation of KE ((1/2)mv^2) because m = vAp.

Disadvantages of wind power

- Unreliable
- Low energy density
- Some consider generators to spoil the countryside.
- Noisy
- Locations are usually far from centers of populations.

Black-body radiation

- Radiation from a theoretical perfect emitter (because black objects absorb all of the light energy falling on it and perfect 'emitter' is also a perfect absorber of radiation => darker the better absorber).
- Depends on temp. (not emitting surface).

Wien's displacement law

- Law that relates the wavelength at which the intensity of the radiation is a maximum λ t0 the temp. of the black body T.
- λmax * T = constant (2.9E-3 m K)
- Radiation emitted from planets will peak at Infra-red.

Stefan-Boltzmann Law

- Law that links the total power radiated by a black body (per unit area) to the temperature of the black body.
- Total power radiated = σ A T^4 (σ = constant = 5.67E-8; A = surface area of the emitter (m^2); T = absolute temperature of the emitter (K)).

Thermal equilibrium

- When the temp. of a planet is constant and the power being absorbed by the planet equals the rate at which energy is radiated into space.

Emissivity

- The ratio of power radiated by an object to the power radiated by a black body at the same temp.
- (power radiated by object)/(power radiated by black body at same temp.)

Feedback

- A process which the result of a change is a further change of one of the constants involved in the calculation.
- Positive- when an action causing global warming is heating up the earth even more.
- Negative - opposite of positive. Leads to a decrease in temp.

Greenhouse effect

- The process which the greenhouse gases in the atmosphere absorb infra-red radiation and re-radiate half of it back down to the earth
- Due to this effect, the upper atmosphere and the surface of the Earth are warmed.
- The right amount will keep the temp. of Earth constant. If it did not exist, the temp. of Earth will dramatically decrease.

Greenhouse gases

- absorb infrared radiation as a result of resonance.
- The natural frequency of oscillation of the bonds within the molecules of the gas is in the infrared region.
- Examples: CH4, H2O, CO2, NO2, O3, CFCs.
- As its vibration increase. the temp. will also increase.

Possible causes of global warming

- Changes in the composition of greenhouse gases in the atmosphere.
- Changes in the intensity of the radiation emitted by the sun.
- Cyclical changes in the Earth's orbit and volcanic activity.

Enhanced greenhouse effect

- Increase in the greenhouse effect caused by human activities.
- Increased combustion of fossil fuels has released extra CO2 into the atmosphere, which has enhanced the greenhouse effect.

Evidence for Global Warming

- Ice core data from Russian Antarctic base at Vostok is used to figure the atmospheric concentrations of greenhouse gases (air bubbles trapped in ice caps).
- The data shows that the variation of temp. and CO2 concentration is closely related.

Mechanisms of global warming

- Global warming reduces ice/snow cover => reduces albedo => increase rate of heat absorption.
- Temp. increase reduces the solubility of CO2 in the sea => increase of CO2 in atmospheric concentration.
- Temp. increase would increase evaporation rate => more water vapor in air (water vapor is a greenhouse gas).
- Temp. increase causes tundra (frozen subsoil) to melt => release CO2.
- Deforestation not only results in further increase of CO2, but also reduced carbon fixation.

Possible solutions to reduce the enhanced greenhouse effect

- Advancement in technology (greater efficiency; fusion reactors).
- Reduction of energy requirements by improving thermal insulation, using energy efficient methods of transports, using combined heating and power systems (CHP).
- Replacing the use of coal and oil.

Fuel

A substance that can release energy by changing its chemical or nuclear structure