Converting Kinetic Energy Into Electromagnetic Energy (Brad Issler)

Converting Kinetic Energy to Electromagnetic Energy Through the Use Of Wind Generators.

Principles Investigated: Conservation of energy, Newton’s laws. Optional: current, resistance, voltage, inductance, AC/DC.

Standards: 3.1, 4.1, 5.4, 6.6, Physics 2, 3, 5.

Materials: Wind powered generator, can be made or purchased as a kit (Green Science, $12 at REI ((plug)). Table fan. Hand crank generators (optional).

Procedure: Set up wind powered generator. Use the table fan to create the “wind.” The discrepant event can be placing the table fan at different speeds and/or angles to the turbine. Let students suggest the possible scenarios for the discrepant event.

Fig. 1. Illustration of a commercial-scale, wind-generator.

Certain parts will not be included with small-scale kits,

e.g., transmission and brake.

Student Prior Knowledge: This demo is appropriate for all levels. The explanations can be modified as appropriate. Of course, basic electrical terminology (high school physics) would be beneficial.

Explanation: Conservation of energy states that matter is neither created nor destroyed; it can only be transformed from one state to another. It is possible to turn kinetic energy (wind) into electromagnetic energy (generator). This can be accomplished using a wind generator.

The wind turns the turbine blades, which turns a shaft to the generator (Windpowersavings, 2010). Inside the generator is a magnet and a metal coil (usually copper). When the magnet spins it induces an electrical current (Wikipedia, Electrical Generator, 2010). The current is directed into the circuit. The product, after resistance is accounted for, is the ability to due work. In this case, work is defined as making an LED illuminate.

In this demonstration, it is appropriate to illustrate the similarities and differences between voltage, current, electrical charge, force, pressure, work, power. I.e., wind generators take kinetic energy and convert it into electromagnetic energy by inducing a current. This current is used to do work, while voltage (the resulting force after overcoming resistance) is the energy required to drive the flow of the current. An effective analogy for this example is the flow of water through a pipe, where voltage is the pressure difference between the two ends of the pipe, current is the quantity (volume) of water flow past a specific point with respect to time, and electrical charge is the quantity of water.

Questions & Answers:

Q1) How does spinning a magnet inside a coil create electricity?

A1) Whenever a circle of wire surrounds a magnetic field, and the magnetic field then, a circular "pressure" called Voltage appears (Brain, 2010). The faster the magnetic field changes, the larger the voltage becomes. This circular voltage tries to force the movable charges inside the wire to rotate around the circle. In other words, moving magnets cause changing magnetic fields, which try to create electric currents in closed circles of wire. A moving magnet causes a pumping action. If there is a break in the circuit then the pumping force will cause no charge flow. Instead, a voltage difference will appear at the ends of the wires. But if the circuit is "complete" or "closed", then the magnet's pumping action can force the electrons of the coil to begin flowing. A moving magnet can create an electric current in a closed circuit. The effect is called Electromagnetic Induction. This is a basic law of physics, and all coil/magnet electric generators use it.

Q2) What is the difference between electrical energy and kinetic energy?

A2) Electrical energy is the presence and flow of an electric charge (Wikipedia, Electrical Potential Energy, 2010). Examples of electrical energy include phenomena such as static electricity, electromagnetic fields and lightning. The concept of electrical energy is defined using a variety of different terminologies such as charge, current and potential. Electrical energy is the result of the interaction of subatomic particles with electromagnetic force. Within an atom, electrons and protons create a charge. This charge can be transferred between bodies using direct contact with a conductive material like a wire. Kinetic energy is the extra energy that an object possesses when it is in motion (Wikipedia, Kinetic Energy, 2010). This motion of the object can be in any possible direction, and there are several different types of motion by which an object can move. Kinetic energy can also be described as the amount of work that it would require for the object to accelerate from a state of rest to its current velocity. The amount of kinetic energy that an object may have is described simply as a magnitude, and does not represent its direction of travel.

Q3) Describe Resistance and how it relates to wind generated electricity.

A3) The electrical resistance of an object is a measure of its opposition to the passage of an electric current. Within the wind turbine system there are two forms of resistance, mechanical and electrical. The mechanical resistance is due to friction between the moving parts. Electrical resistance comes from factors including the size of the electrical wires, the type of metal used, and the temperature. There is a finite amount of wind pressure interacting with the wind turbine. Some of that pressure is absorbed in turning the blades of the turbine and overcoming the mechanical resistance. Finally, the resultant energy is transferred into spinning the magnets inside the generator where more of that initial pressure is absorbed. This resultant energy is transferred into inducing an electrical charge. The resulting voltage used to power the grid, or the LED (in the case of the demo), is Ohm’s law which states that the voltage is equal to the current divided by the electrical resistance, or V=IR.

Applications to Everyday Life: Besides wind powered generators, other renewable resources that can transfer kinetic energy into electromagnetic energy. One of these is geothermal energy where hot water from deep within the earth is pumped to a station where it is separated into water and steam. The steam is used to turn a turbine much like the blades of a wind generator. A second example includes using resources such as sugar cane and corn to create fuels to power motors. The process is similar to inducing current in a generator. The motor produces mechanical work while generator produces electrical energy. The final example includes the use of radiant (light) energy to create electrical energy. This is accomplished by using solar panels. The light energy is captured by the solar cells where it excites electrons. These electrons transfer the kinetic energy through the system where it is converted into electrical energy.

References:

Windpowersavings (2010). How Do Wind Turbines Work? http://www.windpowersavings.com/how-do-wind-turbines-work/14/. Accessed 11/25/10.

Wikipedia (2010/11/21). Electrical generator. http://en.wikipedia.org/wiki/Electrical_generator. Accessed 11/25/10.

Brain, M., Lamb, R. Howstuffworks (2010). How Electricity Works. http://science.howstuffworks.com/electricity2.htm. Accessed 11/25/10.

Wikipedia (2010/11/30). Kinetic Energy. http://en.wikipedia.org/wiki/Kinetic_energy. Accessed 11/25/10.

Wikipedia (2010/11/30). Electrical Potential Energy. http://en.wikipedia.org/wiki/Electric_potential_energy. Accessed 11/25/10.

Wikipedia (2010/11/30). http://en.wikipedia.org/wiki/Inductance. Inductance. Accessed 11/25/10.