Energy and Energy Resources

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Energy is a fundamental concept in physics. It is the ability to do work, which in physical terms is the product of a force applied over a distance. It comes in many forms and can be transformed ("transferred") from one form to another. It is this transfer that makes things happen.

e.g. a battery connected to a bulb has the energy transfers:

chemical potential energy --> electrical energy --> light + heat energy.

We look at the three methods by which heat energy is transferred; conduction, convection and radiation. Finally, and most importantly, we investigate how electrical energy is generated, the nature of fossil fuels and effects of burning them, and different methods of utilizing renewable energy resources.

This unit has a lot a variety within it. The concepts of energy transfer and efficiency tends to be rather straightforward, then we move on to heat transfer, which students often struggle with. The next topics involve the mathematical treatment of energy with concepts such as work, power, gravitational potential energy and kinetic energy. We finish the topic by looking at the energy resources that are used to generate electricity, with a strong emphasis on renewables.

Student booklet - June 2017

2.1 - Energy Transfer

Describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational),
Understand that energy is conserved and know and use the relationship: efficiency = useful energy output / total energy output.
Draw energy flow (sankey) diagrams for a variety of everyday and scientific situations.

2.2 - Heat Transfer

Describe how energy transfer may take place by conduction, convection and radiation.
Explain the role of convection in everyday phenomena.
Explain how insulation is used to reduce energy transfers from buildings and the human body.

There are three heat transfer mechanisms: conduction, convection and radiation.

Conduction is the passing of molecular vibrational energy from one molecule to another. Metals are by far the best thermal conductors, which is why saucepans generally have wooden or plastic handles.
Convection occurs within fluids (liquids and gases). The higher the temperature of a fluid, the more spread out the particles become, which leads to a drop in the density. The less dense fluid then rises above the cooler, more dense fluid. Common mistake: 'heat rises' - should be 'warm fluids rises'. This is the process that drives the weather and ocean systems of the world!
Radiation is the electromagnetic radiation that is emitted from any object above absolute zero. As far as we are concerned this is usually infra-red (IR) radiation. The surface of the Sun and the filaments of lightbulbs are hot enough to emit visible light. IR radiation travels at the speed of light and is the only one heat transfer mechanism that can travel through a vacuum. Dull, black objects are the best absorbers and emitters of thermal radiation, which is why black clothing and cars get so hot during a Bermudian summer.

Island-life.... a beach bonfire is a fantastic way to spend an evening. During the evening, especially when the skies are clear and the stars are out, the sand cools dramatically from warm to cold due to emission of heat radiation to the atmosphere. By 11 pm, the sand is decidedly chilly, but the ocean is still pleasantly warm. The water has a much higher specific heat capacity than sand. Last year a couple of students camped out and measured the hourly variation in temperature of the sand and sea!
(Elbow Beach Oct 2015)

Question: why do the flames go upwards?

A convective Morgan's Cloud forming over Bermuda on a hot summer afternoon. As the island heats up more than the ocean, moisture in the ground evaporates and joins the rising warmer air as the convection starts. As the warm, moist air rises it cools and the water vapour condenses to form water droplets (clouds). Convective clouds like this are typically cumulus (fluffy) in nature. Depending on the moisture content and the difference in temperature they can even form thunderclouds! It appears to be raining in Somerset when I took this photo.

For a sailor, the formation of a overland convective cloud, such as this, is a sure sign that a sea breeze will form on an otherwise calm day. The conditions required are: no gradient wind (synoptic), temperature difference of at least 5 degrees between the ocean and the island.

Spacey Stuff - Science and the Apollo Missions. The astronauts managed to set up probes to measure the surface temperature, but in doing so they disturbed the surface, which changed the absorption characteristics from heat radiation. Fascinating bit of history and how easy it is to foul up an experiment!

2.3 - Quantitative Calculations on Work, Energy and Power

Understand that ‘work done’ is equal to energy transferred and to able to calculate it.

Know that kinetic energy is a measure of the amount of energy of a moving object and be able to calculate it.

Understand that Gravitational potential energy is the amount of energy of an object due to its height above the ground.

Describe power as the rate of transfer of energy or the rate of doing work
understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

\[W=F\Delta x\]

\[P=\frac{W}{t}\]
\[PE=mgh\]
\[KE=\frac{1}{2}mv^2\]

2.4 - Electricity Generation

Describe the advantages and disadvantages of methods of large-scale electricity production using a variety of renewable and non-renewable resources.
Describe the energy transfer chains illustrating the environmental implications of fossil fuels.

Electricity is a fantastic form of energy - it can be used to do almost anything! At the most basic level there are three ways to produce an electric current:

Chemical battery (chemical --> electrical)
Photo voltaic cells (light --> electrical)
Spin a generator (kinetic --> electrical)

You could try catching some lightning, but that is fraught with difficulty, so rather impracticable.

Batteries are portable but low power with a limited energy storage. Solar panels are also low power and less portable. In terms of large scale electrical power we have to spin a generator somehow. There are a wide range of methods with pros and cons.

How does a generator work? Faraday demonstrated in the 19th century that turning a magnet inside a coil of wire induced a current. The size of the current, and hence the energy output, could be increased by spinning the magnet faster, more coils of wire and stronger magnets. Tesla later improved the generator's efficiency by adding more sets of coils and using a powerful electromagnet rather than permanent magnets.

The proposed CETO wave power array for St David's. The idea to use subsurface buoys to power a series of "bike" pumps to send pressurized seawater up to a turbine ashore. This would then turn a generator and produce electricity.

Energy transfer diagram for a standard power station, where a fuel is burned to heat water and convert it to high pressure steam. This steam then drives a turbine that it turn spins a generator.

BELCO does not use this system! Instead the island's power plant consists of some 24 diesel engines that directly spin generators. This is actually more efficient than the large power stations in the real world, but are only practical on a small scale.