# Day 170: Kill-a-Watt

Part one of the final exam– The conceptual set of questions.  I also handed out the Semester 2 Lab Practical they will complete on Tuesday.  A requirement for this part it to do a some pre-planning and answer three simple questions (Posted on Schoology) about it: (1) What is the purpose? (2) What data will you gather and with what equipment?, and (3) How will you analyze the data you gathered to solve the problem?  So far, some very interesting approaches.  It is hard for me to not give any suggestions or help.

General Physics:

Today, the students completed an activity had them calculating the cost of various appliances given some time values.  We set up six stations, each will a Kill-a-Watt meter.  These are awesome little devices that allow the students to make measurements on appliances as the appliance is being used.  Here are the stations we set up:

1.  Comparing the power for a 40-watt incandescent bulb and a 10 energy-efficient compact fluorescent equivalent and how much money over the course of a year could be saved.

2. A microwave warming some ‘coffee’ (or water in this case).

3.  Comparing a Wii gaming system and X-Box 360 (unfortunately we only had the Wii to play with).

4.  A cell phone charger … measure the power with the phone connected and not connected.

5.  A mock kitchen circuit — For this one, we monitored current.  We plugged in a light (100 watt), a toaster, and a stove (or hot plate in this case), and the students recorded how the current changed.  The questions for this station related to parallel circuits and why the current goes up… what would happen if a lamp was added …it would have tripped the circuit breaker.  For next year, I’d love to set up and actual circuit breaker so the students can see this happening.

6.  A Smartboard.  Every science room (10) in our building has a Smartboard.  The students calculated to cost of using all of them for 30 minutes a mod (7 total) for the entire year.

# Day 169: It’ll cost how much??

Well, it is the last unit test for these kids, the electrical circuits test.  I am particually pleased with one of the problems I asked, but not with some of the solutions given.  Next year we are going 1-to-1 with Chrome Books.  I simply asked how much it would cost for 30 school days if the 25% of our student body (so about 500 kids) charged their Chromebooks at school for only 30 minutes each day.   Now, I’m pretty sure this is an UNDERestimate.  The actual answer is about \$25, but some of my students came up with outrageous values 😦  For example \$25, 000 or \$189,000 for 30 days….  it was obvious which students took the time to work through the practice sheet they had been given.  I can’t decide how I feel about it.  I know most are seniors and they have 4 days of school left… but….

General Physics:

Today this group saw the same series of demonstrations about household electricity as the advanced kids did yesterday.

# Day 168: Household Electricity

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 167: The end is near…

The was a tough day.  The kids were off for 4 days (some for 5) because of a set of field trip and the senior trip and the Memoria Day weekend.  We started out by discussing the schedule for the rest of the year and the final exam.  For this group of kids it will take place over three days.   The first day (Friday, May 29) will be the conceptual part, on Monday June 1 comes the problem set, and June 2 during the 80 minute exam block will be the final challenge lab.  To wrap up this electricity unit, they will have a summative test on Thursday.  So, only two teaching days left.

We discussed the complex circuit assessment they took the previous Thursday (I know, nothing like immediate feedback), then WB’ed the rest of a set of problems.

General Physics:

These kids have been off even longer because of the senior assembly… pretty hard to keep them going when then are out of class more than in class.  Today we finished the Circuit ILD.  They now have all the models for electric potential difference, resistance and current in series and parallel circuits.

# Day 166: No classes for me today

Remember me mentioning he senior trip in my last post?  Well, today was the day they took to seniors to Great America in Gurnee, IL.  Nope, I did not go.  Why you ask?  I have a glass stomach… simply looking at those rides up close makes me nauseous.  I know, a physics teacher that can’t go on rides??

So what did I do today.  Well, with the juniors I had left, (which was very few) I offered them a chance to complete any re-assessments still hanging out there.  I also had them get started on viewing a Power Point I had posted on Schoology.  It takes everything we have done with circuits and extrapolates it to our houses.   One of the more important aspects is seeing how series and parallel circuits are used in our homes and calculating the cost of using various electric appliances.  over the next day or two we will look at some practical demonstrations, including causing a house hold circuit breaker to trip because too many appliances are being plugged in.

# Day 165: I sort of hate this time of year and a Complex Circuit Assessment

Yeah, I know, a bit hard to believe me when I say I hate this time of year.  It’s not that I don’t like or absolutely need my summer, but there is so much that is happening.  Senior scholarship ceremony, senior award ceremony, senior trip, graduation, final exams, and grading of final exams….  We hardly have time to celebrate all that the physics kids have learned and done.  I realize that this is totally my fault… I need to create ways for this to happen and to communicate it.  Capstone (or end of year ) projects? Just more for me to think about.

Today the students took a complex circuit assessment:

After the assessment, we started WB’ed a set of circuit problems.  It is a nice set that includes some old AP-B tests.

General Physics:

I saw my Mod 4 class, but not Mod 7.  During mods 6 and 7, the Fire Marshal talked to the seniors about fire safety in a dorm room, and during mod 7 the Senior Award Ceremony was held.

With the Mod 4 class, we completed the bulk of the circuit ILD.

# Day 164: Differentiate This…

Sorry for the calculus based title… I was going for a title related to how I differentiated my plans today… guess I missed.

This was the class I differentiated to some extent.  I offered two (well three) levels of problems related to using Ohm’s Law and the related series and parallel equations to determine the values on a number of ammeters and voltmeters in the circuit.  Here are the two problems I offered:

This was the easier of the two.

This was the more challenging:

The students could choose either problem and work in groups of two or three’s.  To help solve these, i really strongly (ie force) my student to simplify the circuits using the equivalent resistance equations and redraw as they go.  It has been my experience that this helps the students immensely.

On a side note, I found it really interesting that some of my students with a better background (the kids in our engineering academy) at first did not do the redraws. The had no trouble determining the total resistance and total current, but were dead in the water when trying to find the values of the other meters.  A few told me, they (engineers) would never do this… if you want to know the reading at a certain part of the circuit, grab a multimeter and measure it.  I asked about an instance when y wanted to add a motor to a branch of a circuit and the motor had current anc voltage specs and how they would determine what resistance to add and how to get the motor specs correct?  They really did not have an answer.

General Physics:

Just more on the circuit ILD… sorry not too much exciting here.

# Day 163: Final Jeopardy

Well, we finally finished the Circuit ILD.  The last set of circuit predictions was a parallel circuit with 3 different resistors all on separate branches.  The prediction was about comparing the voltmeters across each resistor. I like this one because it plays on the students wanting the smallest resistor to have the smallest potential difference across it, BUT it is a purely parallel circuit.  Those groups that drew an electric potential diagram had no problem correctly predicting that the potential difference values were all the same.

As a bonus question, and just to make things interesting… I asked a final bonus question. It was asking the students to predict the how the values on the given meters would change when one resistor is removed… a pretty classic conceptual question.

The middle resistor (R3) was disconnected.  The student groups were asked to explain how each meter changed (increased, decreased, or no change).  To make the question more interesting,  I turned it into a “Final Jeopardy’ style question.  Each group could wager any number of points they had earned though out the entire activity.  In my humble (or not so humble) opinion,  this was GENIUS.  All of a sudden, groups that had no change to win, were back in it!  The group had to get all 5 meters correct to earn the wager points.   I shot some video as the students worked on the problem:

And yes… I did have the jeopardy theme playing on a continuous loop in the background as they worked.  Genius, absolute genius.

General Physics:

This group is catching up to what the Advanced groups are working through.  Today they took the equivalent resistance assessment and started the Circuits ILD.  For the most part, the version we work on with this group is the same.  We add a circuit or two so the conceptual jumps are not quite so big.

# Day 162: A WB’ing practice plan that rocked (IMHO)

Just more work today on the Circuits ILD… but I will add that after checking the final parallel circuit, not only were most students able to give me the junction rule, but they could also explain the majority of the observations from the earlier circuits we had glossed over (or they had incorrectly predicted).  I love not lecturing…  One more circuit to check tomorrow with voltmeters and then we’ll play with how the ammeters change (in parallel) when one bulb is removed.

General Physics:

We had to come up with a plan, well actually a sub plan for my last class of the day and my colleague’s class (he is the head girls track coach). I usually cover his class when he is gone for a meet, but today I had the pleasure of sitting in on three interviews for a new district level position.  It is for a k-12 Math/Science/STEM Coordinator, yes one person for one position…

So anyway, the plan that I used was a version of one a colleague had taught me four or five years ago.  I was able to test run it with one of my classes before I left for the interviews.  I put the class into 8 groups of three. Each group grabbed a big WB, drew a source, one wire and one resistor. The group also labeled the value of the resistor.  The board was then passed over to  the next group that also added a wire and a labeled resistor.  This continued until the board made it back to the original group, and viola… a totally unique equivalent resistance practice problem:

The ower of each board used a second large WB to solve the problem.  Once finished, they traded problem boards with another group and worked a second problem.  This provided another problem and a chance to see if the group had solved the first problem correctly.  The dialogue between the two groups was AWESOME as they discussed which solution was correct if the two did not match. Yep, I have to write that idea own where I can see it.. even the students commented that it was a good approach to the practice… so yeah IMHO it rocked.

# Day 161: Circuits ILD Continued

The students started the hour by completing a formative assessment on determining the equivalent resistance of a circuit containing eight resistors.  Here it is:

It really was formative… nearly every student (well, maybe except 3 or 4 in each class) totally nailed it… no need to re-assess or re-teach. For those that need it, I posted some practice on Schoology.   Love formative assessment.

The remaining time was spent working on the Circuits ILD. We completed the circuit that asked the students to predict the size of the reading on 3 voltmeters across three resistors in series (R1=R2>R3).  Most groups predicted ΔV1>ΔV2>ΔV3, because of the order they appeared in the circuit.  A bit disappointing because we have worked on drawing electric potential diagrams.  Once the groups saw the results, they quickly realized that the location had nothing to do with the value… I’ll have to find a way next year to try to address this as we practice with the EPD’s… maybe just asking about changing the location of bulbs in Bulb Boy.

We also looked at parallel circuits:

This one was for the same two resistors that were wired in series in an earlier circuit.  I like this photo because it shows good the data is… just wish I had the circuit a bit more scrunched in so you could compare the brightness like the students did in class.  Speaking of students, here are two shots of the students preparing predictions:

Tomorrow we will work with three resistors in parallel and add the voltmeters back in.  I still have not given them the ‘official junction rule’ yet… they have only worked with two parallel circuits.  They have formed some ideas as to how parallel circuits behave and tomorrow we will do one more. or maybe two before we discuss and I let them throw the rule out to me.

General Physics:

They learned about resistances in series and parallel  and completed the same sample problem the advanced class did.  I like it when the generals do the same thing as the advanced… it gives them some confidence.