Today we discussed house hold applications of the elctrical concepts developed in the unit. This is the only day of the entire year I used a power point. I posted it last night so the students could (hopefully) look through it before we discussed it. I centered it around how what we developed with little bulbs and cells still basically applies to houses also. There were several demonstrations along the way: (Sorry, forgot to take pics)
1. To differentiate between DC and AC: I connected a set of 2 D cells to a Vernier voltage probe, and gathered 5 seconds of data. Nice horizontal positive electric potential graph, switch the polarity and gather again, a nice negative graph… but still constant and in one direction hence direct current.
2. I used a magnet, a pick-up coil and a galvanometer as a little generator to show electromagnetic induction. We also have an old hand generator that I connected to a strange little AC bulb. It shows that the light alternates back and forth. I then connected an AC source to the Vernier voltage probe and collected some data.. it shows the graph alternating between +V and -V… hence alternating current.
3. Showed them a circuit set up with some bi-color LEDS. Connected to an DC source and spin, a solid circle or either red light or green light is seen. Now connect it to an AC source and spin and the circle of light is red-black-green-black… as it spins. Nicely shows how the electric potential drops to zero.
4. I set up a little circuit… a lamp, a fan and a hair dryer. These were plugged into a power strip and a modified outlet (set up to connect an AC ammeter and voltmeter) and turned on one at a time. THe students can see the current increasing as the devices are added because resistance is dropping. I would really like to be able to set this up with a circuit breaker so it would trip as I continue to add devices.
5. Finally we learn how to use the electric potential, the current and the time a device is used, along with the charge per kilowatt-hour to determine the cost of using a device. The device we used wa a hot dogger. A rather crude device with two nails connected to a cord that is plugged into the modified outlet. We time how long it takes to cook the hot dog, then calculate the cost.
Today was all about complex circiuts for this group. They also worked in small groups to solve an easier problem with multiple meters. Tomorrow, we will have the same house hold electricity discussion the Advanced kids had today.