8.1+Energy+degradation+and+Power+Generation+Notes+2011

Back to IB PHYSICS > ENERGY, POWER AND CLIMATE CHANGE > PHYSICS CLASS 2011 COLLABORATIVE NOTES PROJECT You should write notes on the section which is allocated to you. Make sure your notes are easy to understand and include pictures, links and examples where appropriate. Explain the formulas from the data booklet where necessary. On each page, you will see the syllabus references. To write notes, click on EDIT. You can then write, insert files and pictures or links. You could link to useful web resources, java applets etc. You can obtain information from the text books or the Internet. You must login to be able to edit and you must be a member of the wiki.

Deon || 8.2 World energy sources Notes 2011 Zac || 8.3 Fossil fuel power production Notes 2011 Bevis || 8.4 Non-fossil fuel power production Notes 2011 Reilly, Luke, Ryan || 8.5 Greenhouse effect Notes 2011 Luka, Antoine || 8.6 Global warming Notes 2011 Ivy, Matteo || =8.1 ENERGY DEGRADATION AND POWER GENERATION (Deon)= ** Aim 7: ** Computer simulations of Sankey diagrams feature here.
 * 8.1 Energy degradation and Power Generation Notes 2011

8.1.1 State that thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.

The continuous conversion of thermal energy into work requires thermal energy to be transferred to the surroundings. From the law of the conservation of energy, it may seem possible that this energy is then caught again to use it in a perpetual motion machine. However, this is not possible because for a continuous, cyclical conversion of thermal energy to occur, energy has to be lost to the surroundings, which consequently means the system requires a constant input of energy.

Therefore, the second law of thermodynamics states that:

// It is impossible to take heat from a hot object and use it all to do work without losing some to the surroundings. //

8.1.2 Explain what is meant by degraded energy. Students should understand that, in any process that involves energy transformations, the energy that is transferred to the surroundings (thermal energy) is no longer available to perform useful work.

Degradation of energy is the process of energy transforming into disordered, spread out energy. Thermal energy is described as the most degraded form of energy, as it is the final form energy that is 'spread out' or lost to the surroundings in any conversion, and ultimately becomes unavailable to perform useful work.

The reason for this is due to the nature of matter. Using an example on page 266 of the textbook:

A block is dropped from a height above the ground. The result will be the PE of the block held above the ground transforming into thermal energy when it hits the ground. This is due to the energy spreading out between the molecules in ground and the block upon impact.

Whenever energy is transferred, some energy spreads out, and when it has spread out, it cannot be reused. This explains why machines are never 100% efficient, and why perpetual motion machines can't ever be created. Furthermore, this implies the possibility of a time when all energy in the universe will be in the form of heat, as usable energy will be constantly lost, without gaining. The application of this fact is that it will be impossible to do any work at such a time.

8.1.3 Construct and analyse energy flow diagrams (Sankey diagrams) and identify where the energy is degraded. It is expected that students will be able to construct flow diagrams for various systems including those described in sub-topics 8.3 and 8.4.

Sankey diagrams illustrate the flow of a system. In relation to this topic, Sankey diagrams can be used to display the flow of energy, i.e. how useful energy is produced.

The following diagrams, obtained from http://www.ipodphysics.com/sankey-diagrams-work.php (who got it from Cyberphysics), show how Sankey diagrams are drawn:



8.1.4 Outline the principal mechanisms involved in the production of electrical power. Students should know that electrical energy may be produced by rotating coils in a magnetic field. In sub-topics 8.2 and 8.3 students look in more detail at energy sources used to provide the energy to rotate the coils.

Electricity is a very useful form of energy because it can be easily transferred from one place to another, using wires. This makes it much more efficient in terms of time and energy, compared to previous, more commonly used forms of energy like coal. To use energy from coal directly in a house, transporting it will take more energy than transporting electricity.

Electricity can be transformed from many different types of energy sources, and all of these types of energy require a generator to convert mechanical energy to electrical energy eventually.

A generator uses the same physics concepts as in Chapter 6 - fields and forces: A charged object moving through a magnetic field will experience a force. In a wire for example, the force causes electrons to move to one end in the wire. A p.d. is then created, which in turn can be used to induce a current in a circuit. In a generator, instead of a wire, a coil rotates in a magnetic field. This rotation causes an alternating current.

The following link, taken from the textbook, uses a helpful simulation to explain how electricity is generated: Interactive Electric Generator