Allen High SchoolIB Physics SLSource: Chris Hamper SL Physics

8.1 Energy Degredation & Power Generation We remember that energy cannot be

created or destroyed only transferred by doing either work or transferring thermal energy (friction).

The energy that is transferred to its surroundings (thermal energy) becomes unavailable to do work. This is Degraded Energy. This is part of the second law of Thermodynamics (Entropy).

Examples of Energy Transfer Light Bulb

Converts electrical energy to light + heat Motor

Converts electrical energy mechanical + heat Battery

Converts chemical energy to electrical + heat Car Engine

Converts chemical energy to mechanical + heat

Solar Cell Converts light to electrical + heat

Sankey Diagrams

Sankey Diagrams are used to visualize the flow of energy as it changes from one form to another.

The thickness of the arrow (band) represents the proportion of energy of each kind.

The direction is typically left to right, with degraded energy angled down .

Be sure to label the type of energy for each.

Examples of Sankey Diagrams

Power Generation

The goal: Electricity! The “how”: a Generator

A generator is a device that converts mechanical energy into electrical energy. This is what a power plant does.

By the way, a motor does the opposite; it converts electrical energy into mechanical energy (think of a household fan).

E & M

You previously learned a connection between electricity and magnetism. This is the foundation of a generator.

If a coiled wire is rotated in a magnetic field, a current is induced in the wire. Sometimes a side of the wire is moving up and sometimes down, this is what produces Alternating Current (AC).

Diagram of a Generator

A basic generator has looped wire (coil) that is rotated in between a magnetic field (present because of an existing magnet) and as a result, current is induced in the wire.

The rotation actually can wear down the wire and thus, many generators choose to move the magnet instead of the wire.

(Next Slide)

Foundation of a Generator Notice the motion of the magnet, the

direction of current, and meter reading.

8.2 World Energy Sources

With the knowledge that there is always some energy degraded, you must have a source that is sufficient enough to provide useable energy and the degraded energy.

The source of energy is called a Fuel. Fuels release energy by changing its chemical or nuclear structure.

There are many different sources of fuel in the world.

Fuel Sources

There are two main categories of energy:

Non-RenewableCoalOil & GasWood & BiomassNuclear Fuel

Renewable (from Sun)Solar EnergyHydroelectric PowerWind PowerWave PowerRenewable (not derived from Sun)

Tidal Power (due to the oceans grav. pull with moon.)Geothermal Energy (tectonic plate friction; geysers)

Non-Renewable Fuels

Coal Composed from matter that died millions of years

ago. Over time, intense heat and pressure transformed into coal, one example of fossil fuel.

To retrieve the stored energy in the coal, you have to first dig it up (coal mines) and then burn it, both of which have environmental impacts.

It has a limited supply. The rate at which it is being used is much greater than the rate of production. We may only have enough coal for 150 more years.

Non-renewable Fuels

Oil/Gas Now more heavily used than coal. Oil/gas are

examples of fossil fuels. Oil/gas are easier to extract than coal (pumps instead of mines).

Oil/gas has to be burned (like coal) to release its energy. That energy powers an engine. Burning oil/gas also has environmental impacts.

It is unknown how much oil/gas remains for the future, however in 2003, it was estimated around 1 x 10 14 litres.

Non-renewable Fuels

Wood/Biomass For ages, wood has been burned for heating

and cooking and this continues today. Sugarcane (and other plants) produce oils

that can be used to produce biofuel that can power cars.

Food waste can also be used to produce fuel (as well as cow manure). However, these are not high grade fuels (see energy density later).

All the above have to be burned for use, therefore having environmental impacts.

Non-renewable Fuels

Nuclear Fuel Nuclear energy does not come from the

sun. Nuclear fuel materials have unstable nuclei that can split and give off energy.

Nuclear fuel does not have to be burned, however it does have radioactive waste and is difficult to dispose of.

Like coal, nuclear fuels (like uranium) have to be extracted from the ground and then purified for use.

See Nuclear Power in 8.3/8.4 PowerPoint also.

Energy Density

Some fuels are more efficient than others, we categorize this as Energy Density.

Energy Density is the ratio of the Energy produced to the mass required (unit: MJ/kg).

Fuel Energy Density (MJ/kg)

Fusion fuel 300,000,000

Uranium-235 90,000,000

Gasoline (Petrol) 46.9

Diesel 45.8

Biodiesel 42.2

Crude oil 41.9

Coal 32.5

Sugar 17.0

Wood 17.0

Cow dung 15.5

Household waste 10

Renewable Fuels = The Future Solar Energy

Collecting the sun’s energy directly. Mirrors can focus a “hotspot” to collect the energy that can be used to power engines that can do work.

Photovoltaic cells can also collect and store the sun’s energy to power buildings and homes.

Of course, this is only useful on sunny days and places with a good source of sunlight.

Renewable Fuels

Hydroelectric Power The principle begins with rain!

The Sun heats the ocean and turns into water vapour, which then produces clouds, which leads to rain. When water rains onto a mountain, the water has a high PE. This energy can do work as the water runs down the mountain.

Water wheels were an early discovery; utilize falling water to generate usable energy.

Renewable Fuels Wind Power

Warm , less dense air moves upwards = Wind.

In the last couple of decades, more wind turbines have popped up as sources of energy.

The kinetic energy of the wind turns a fan, which turns a coil (in the presence of a magnetic field), which generates electricity.

Denmark produces 20% of its electricity from wind power.

Renewable Fuels

Wave Power Water waves spread out their energy

that arrives at beaches all around the world.

This energy can be used to power turbines and produce electricity.

With today’s technology, it is now more viable to use wave power more than ever.

Worldwide Consumption of Energy