Day 168: Household Electricity

Advanced Physics:

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.

General Physics:

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.

Day 155: Retirement…

No, not mine ( I can’t even begin to fathom it yet).  Two come to mind this week.  The first is a long-time colleague from another high school.  This colleague has also been one of the regulars at our Phox Valley Share sessions over the last bunch of years.  She works at parochial school in town and will be very difficult to replace… OK, not the right word, but you know what I mean. She teaches biology, chemistry, and physics — at a PAROCHIAL school.  She continues to work very hard and still has her students working hard too… very cool.

The second is one of my older sisters ( I have four).  This one has been teaching for a total of 27 years.  The last 20 have been at a high school in the southern part of the state (just outside of Milwaukee).  My brother (a district level administrator in the one of the bigger districts in the state) and I surprised her by showing up at the dinner and ceremony her district held to honor its retirees and 25 year employees.  My sister was speechless, which I can tell DOES NOT HAPPEN very often!  She just sort of stared at us for the first 20 seconds… then started to cry.  It was a very nice meal and ceremony. It was amazing to hear about the things my sister has done for her district and school.

The power of relationships keeps popping into my mind as I reflect on these two retirements. The professional relationship with my colleague and the family relationship with my sister remind me that when there are solid relationships in place, amazing things can happen.  Easily transferred to the classroom setting… strong relationships with students can help them achieve amazing things.  I know I have not established the relationship with every student,  something for me to continue to work on.

Advanced Physics:

We started this class by looking at how the electric potential difference changes around a circuit.  I used these two circuits along with a Vernier voltage probe to build the idea of an electric potential diagram (an EPD).


To draw the EPD, the end of each wire is labeled with a letter:


The potential is measured by placing the black lead of the voltage probe on the wife labeled ‘F’. and the red robe starts on the wire labeled ‘A’.  Collect the potential difference values as the red lead is moved to each of the labeled positions.  This provides the values for the EPD.  In the end, here is what the EPD’s will look like:

Screen Shot 2015-05-10 at 4.31.31 PM Screen Shot 2015-05-10 at 4.31.36 PM

I like these diagrams because they show that the only time the electric potential difference drops is across a bulb, NOT along a wire, especially these short wires.  This type of diagram  is similar to the color coding for electric potential used with CASTLE. The only issue I have had with that process is choosing appropriate colors when the circuit is not a nice, clean one with the obvious colors.

Toward the end of the hour, I have the classes a situation to draw both the schematic and the EPD for.  Here is a clip of the demo that uses a bath room light bar I re-wired.

General Physics:

This group spent today completing the Bulb Boy activity.