| Building Generators |
| Physics Section Week # Day # Building Generators Science Probe 10, Chapter 6, pp. 112-115 Theme: Problem Solving PLOs addressed: �describe he interactions between magnetism and electricity and relate these to common devices� �apply knowledge and data to make recommendations for reducing energy waste� Objective(s): To apply knowledge about the movement of electrons to construction of an electric device. Materials: Teacher�s Background Info: An electromagnet shows that flowing electrons produce a magnetic field. The reverse is also true. If you move a magnet past a coil of wire (as in an electromagnet), electrons will move along the wire as long as the magnet is moving. But, you need high speeds to generate a measurable current. It would take a very sensitive instrument to detect the tiny current generated by simply pushing a magnet through a coil. An easier way is to use a battery operated DC motor as a current generator without the battery. Estimated Time for Activity: 90 min. (over two classes) Content Students will work in groups of four to create generators. Teacher will select a range of energy sources (e.g. wind, water, human energy) and students will pick one type of generator to construct. Students can be told about the project before a weekend and will have time to plan and to gather materials. An entire lesson will be devoted to constructing the generators. During the lesson, teacher will assist the students and will ask them questions about the generator relating to E and M concepts studied in the course. For example, current induction, magnetic fields, efficiency. In fact, a portion of another lesson can be devoted to getting energy input and output readings from the generators and using these to do efficiency calculations. Sample generator projects: In a simple hand crank generator the magnet is fixed and the coil of wire moves. Because the coil rotates, the direction of the magnetic field changes in relation to the coil. This changing direction of the magnetic field causes the current that flows in the coil to change direction as well. Thus, the current produced is alternating current. 1. How could you use an extension cord to produce electricity? The obvious answer is to plug it into the wall outlet. But this challenge is a little more difficult than that. 2. Challenge: Use only a 50 ft extension cord hooked to a galvanometer and produce electron flow. 3. After students puzzle over this for a little while suggest to them that if magnetic force lines are cut with a conductor electrons should flow. Remind them that the largest magnet in the world is the entire planet. Remind them that there are magnetic lines of force going around the world from pole to pole. 4. If no one has still come up with an idea, suggest to them to use the extension cord as a jump rope. As they twirl the cord they will be cutting the magnetic lines of force around the earth. 5. Details that must be attended to are: a. The cord must make a loop with both ends hooked to the galvanometer. Do this by attaching an alligator clip to the ground prong of the cord and via a short piece of copper wire to one terminal of the galvanometer. b. Jam another alligator clip into the ground receptacle on the other end of the extension cord, and attach this, via a short piece of copper wire, to the other terminal of the galvanometer. c. Align the extension cord in the east/west direction. Why? [When the cord is turned we want it to perpendicularly cut the lines of force that are going north/south.] d. Leave both ends of the extension cord on the ground and pick up the middle half and twirl it like a jump rope (you will need two twirlers.) e. What effect does the rotational speed of the cord have on the deflection of the galvanometer? [The faster the turning the greater the deflection of the galvanometer.] Hydropower Generator (IMAGE) Assessment/Evaluation: Assess generators for care and function, assess student responses to verbal and assigned questions. |