IB Physics SL - CHAPTER 8

Specific energy

Specific energy is the measure of the amount of energy per unit mass of a fuel. (Unit: J/kg)

Energy density

**Energy density** is the measure of the amount of energy per unit **volume** of a fuel. (Unit: J/m^3)

Density from energy density and specific energy

Density = Energy density/Specific energy

Sankey diagrams

Represent energy transfers.

Primary energy source

A primary energy source is one that is found in the natural environment.

Secondary energy source

A secondary source is processed or refined primary resources (into useful energy).

Renewable energy source

A renewable energy source is one that is reproduced at a higher rate than it is consumed.

Non-renewable energy source

A non-renewable energy source is one that is not reproduced at a higher rate than it is consumed.

The 3 main uses of energy resources

1. Transport

2. Electricity generation

3. Heating

Solar heating panels

Solar heating panels use thermal radiation to warm water.

Photovoltaic cells

Photovoltaic cells use light to create energy.

Advantages of solar panels

• Unlimited supply of energy

• Clean to produce the electicity

• Freely available everywhere

• Cheap maintenance

• No fuel is required for energy

Disadvantages of solar panels

• Impacted by poor weather

• Limited efficiency

• Only available during the day

• Requires large investment upfront

• Needs large areas

The equipment involved in nuclear power

Control rods: Absorb neutrons.

Moderators: Slows down neutrons.

Shielding materials: Absorb hazardous radiation.

Uranium fuel: Producers heat when reacting.

Water: Turns to steam and turn turbines.

Advantages of nuclear power

• Extensive reserves of fissionable materials

• Increasingly refine technology available

• No greenhouse gases produced

• A large amount of power is produced

Disadvantages of nuclear power

• Hazardous radioactive waste materials produced

• Dangerous if the power plant goes significantly wrong

• Danger of misuse of nuclear material (nuclear bombs)

• Problems with mining fuel

Calculating power obtained from nuclear power

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The equipment involved in burning fossil fuels

Boiler: Burns fossil fuels.

Condenser: Cools water.

Fossil fuel: Produces heat when burned.

Water: Turns to steam and turn turbines.

Advantages of burning fossil fuels

• Extensive infrastructure in place

• High energy density of fuel

• Available energy at any time

• Well-known and developed technology

Disadvantages of burning fossil fuels

• Produces greenhouse gases

• Unsustainable

• Produces pollution

Calculating power obtained from burning fossil fuels

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The equipment involved in wind electricity generators

Wind generators: Uses wind to turn turbines.

Advantages of wind electricity generators

• Clean energy generation

• Freely available

• Is always sustanable and will never run out

Disadvantages of wind electricity generators

• Not consistent energy production

• Needs favourable local conditions to be placed in windy locations

• Can by visually unappealing

Calculating power obtained from wind electricity generators

P = 1/2 · pAv^3

The equipment involved in hydroelectric power

Reservoir: Stores large bodies of water high up.

Dam: Holds water in its reservoir.

Control gate: path leading water to turine

Advantages of hydroelectric power

• Clean energy generation

• Sustainable

• Can be stored for when needed

Disadvantages of hydroelectric power

• Large areas and changes to the environment are needed

• It relies on suitable locations

• A large initial investment is required

Calculating power obtained from hydroelectric power

P = mgh/∆t = p∆Vgh/∆t

Conduction

Conduction is a method of thermal energy transfer that occurs when two solids come in physical contact with one another.

Conduction occurs by

1. Atomic vibrations, or

2. Free electron collisions

Convection

Convection is a method of thermal energy transfer that occurs due to the movement of atoms in liquids and gases, resulting from variations in density within the liquid or gas.

Convection occurs by

1. Convection current

Thermal radiation

Thermal radiation is a method of thermal energy transfer that occurs by means of electromagnetic radiation normally in the infrared region.

Thermal radiation occurs by

Electric charges within the atoms in a material vibrate causing electromagnetic radiation to be emitted.

Perfect black-body

A perfect black-body is an object that absorbs all radiation incident on it and does not reflect or transmit any radiation in return.

Wien’s displacement law

The formula is:

Stefan-Boltzmann’s law

The formula is:

The solar constant

The solar constant is the amount of solar radiation across all wavelengths that is incident in one second on one square meter of the Earth’s athomosphere at the mean distance of Earth from the Sun.

Albedo

Albedo, *a*, is the proportion of radiation incident on and scattered by a given surface.

a = total scattered power/total incident power

Albedo of a planet

Albedo of a planet is the ratio between the total scattered radiation and the total incident radiation of that planet. (Earth = 0.3)

Earth’s albedo varies daily because

• Time of year

• Latitude (North/South/etc.)

• Terrain

Emissivity

Emissivity, *e*, is the power radiated by a surface divided by the power radiated from a black body of the same surface area and temperature.

e = power radiated by an object/power emitted by a black body

Greenhouse gases

Most effect

• Carbon dioxide

• Water vapor

Less effect

• Ozone

• Methane

• Nitrous oxides

Consequences of global warming contributes to even warming conditions

• Ice and snow will melt (darker surface)

• The solubility of carbon dioxide in the sea will decrease (more carbon dioxide in the atmosphere)

• Surface water will evaporate (more water vapor in the atmosphere)

Calculating power obtained from solar panels

Power = Area · Intensity · Time · Efficiency