# Day 160: Circuits ILD and WB the Mother Part 2

After discussing the schematic and electric potential diagram assessment, we started a an activity that will last two or more days.  It is a Circuits ILD. An ILD is an Interactive Lecture Demo. The instructional goals of the activity are to establish the relationships for current in series and parallel circuits. You know … current is constant in a series circuit (It=I1=I2=I3…) and the ‘junction rule’ for parallel circuits (It=I1+I2+I3..).

ILD’s are not really a new concept. I think this topic lends itself very well to an ILD.  The Adv Phys Circuits ILD is a way for me to help the students learn the concepts without resorting to a lecture or a purely inquiry investigation. I have also found it really helps bring some common misconceptions about how current behaves to light (no pun intended this time). For example, take a look at circuit #1, many student think the current is the same because the resistors are the same size OR that the reading on A1 is the largest because it is the first one and the current has not “gone through” any resistors yet, making A3 the smallest because it has gone through two resistors.  To check the first belief, circuit #2 adds a resistor and changes the value.

A really important aspect of the ILD (in my mind) is to actually check the values the students are predicting so they can see the results first hand.

So, here are some specifics about the set up and how I run it in my classes.  The resistors in the ILD are bundles of christmas tree lights. Why these lights?  Well, they are cheap and plentiful and they provide a visual for the students as we check them. The source is simply a 9v battery. Here is a picture of one of the circuits set up and ready to check:

In class, I put the students into groups of three based on the results of some recent assessments. I put a green, a yellow and a red (see this post of the info on these colors) if possible.  I hand out each circuit one at a time and have the groups discuss and make predictions on a big WB. When all the groups are ready, we hang the boards, discuss a bit then actually check the values as shown above.   I do not explain the ‘why’ this is the answer until after a few circuits have been worked through.  I want the students to come up with some ideas to base the predictions on, then allow them to check it with the next circuit.  If I sense that things are going south or the students are getting really frustrated because they are not catching on, then I might provide some small group ‘hints’ as I am walking around.  Some years we even turn it into a competition.. wich group gets the most predictions correct.  More tomorrow about the remaining circuits.

General Physics:

Today was the WB’ing of the Ohm’s Law experiment. We followed the same basic process with this group that we did with the advanced group.  There was one slight change… to see if the material makes a difference, I had the students use the DMM to check the resistance of the ‘sister spool’ from a different set of spools.  The set we used in the experiment was Ni-Cr, and the other (older) set is NS.

# Day 159: Determining Equivalent Reisistance and The Mother of Ohm’s Law Labs take 2

So it is essentially the last day of AP testing  that will decimate my morning classes.  Today the students took a schematic diagram and electric potential difference assessment:  Here it is:

I think it is important for students to be able to create and interpret schematic diagrams… somewhat like force diagrams.

We then completed a group practice problem solving for the equivalent resistance.  Here it is:

One of my goals here is not to make all my students experts, but to continue to practice their higher order thinking skills and problem solving skills.  The next step will be to insert some meters (both ammeters and voltmeters) and ask the students to solve for the values the meters will show.  The remaining time was small group work time with me answering questions along the way.

General Physics:

This crew also completed an assessment on drawing schematic diagrams (no EPD’s for this group).  Here si the one they took:

After this was completed they gathered data for the Ohm’s Law experiment using the spools described in the last few posts. Tomorrow we will WB it.

# Day 158: R in S and P

That stands for Resistances in Series and Parallel.  This is usually one of my favorite experiments.  It is easy to gather the data and the results are always spot on. The experiment graphically develops the equations for resistance sin series (Rt=R1+R2+R3…) and parallel (1/Rt = 1/R1 + 1/R2 + ….) But… this year, thee was just no time to do it.  Here is the way we usually completed it.  It is patterned after an article i read in The Science Teacher a number of years ago.

We use a set of about a dozen fixed resistors with an ohmmeter and a Pasco Circuit board.  Very simply, the students measure the resistance value of each individual resistor, the pick one to hold constant. They wire the remaining resistors (one at a time) in series and measure the total resistance. They plot total resistance vs. resistor 2.  Here is a picture and some sample data:

And the parallel…

But, as mentioned, not time left to do it this year, so we just developed it qualitatively with the spools:

After a schematic circuit diagram assessment, we will practice simplifying a complex circuit, .  More on that tomorrow.

General Physics:

We finished the Mystery Boxes activity and then practiced a bit for a schematic diagram assessment tomorrow also.  We then had a short pre-lab discussion for the Ohm’s Law experiment.

# Day 144: Electric Force (Paradigm) Lab and “Ba Bam!!!”

Today we whiteboarded the last question on the charge practice sheet.  Here is it:

It is chance to have the students confronted with another N3L question.  Most of the students saw that is the electric force exerted on A, by B was the same size as the electric force exerted on B, by A.

It also provides the perfect introduction to an electric force experiment.  I simply ask what the students think the magnitude of the electric force depends on.  They quickly suggest the amount of charge on each balloon, and the distance separating the two objects.  And… right there is the purpose of the experiment… determine the relationship between the electrostatic force and the charge on each object and the relationship between the electrostatic force and the distance separating the two objects.

We use a simulation to gather the data because, well, because it is MUCH easier than trying to really get accurate and quantifiable data. Here is the handout Electrical Force Simulation(13-14)I give the students, it includes a screen shot the simulation screen.  Here is a link to where I found the simulation last year.  I like this one because it does not give too much away and allows a variety of charges and distances.  Tomorrow we WB the results. and develop Coulomb’s Law.

General Physics:

Today we finished the How Hot Are Your Hot Wheels activity; I told the students at what point I wanted them to predict the velocity of the car, so where I would place the photogate.  If you read yesterday’s post, I was concerned about getting accurate velocity data needed in order to determine the dissipated energy and the frictional force.  Well here is screenshot of a group that used a Vernier Photogate to gather the data and to predict and check the velocity.

That’s what we call a “Ba Bam”… nailed it.  Here is a screen shot of a group that used the BeeSpy photogate for the entire experiment:

And again, another Ba BAM!

Moral of the story, if the students are careful when gathering the data, the results are awesome.  Seriously, how awesome are those results??  Pretty ‘darn’ awesome.  PHYSICS ROCKS!

SIDEBAR —> I still have to collect some from each class, and I’m pretty sure there will be a few that are not that close.

# Day 99: Checking the Toy Airplane Problem and The Mistake Game

I started the hour by sharing the results of the student survey my students completed yesterday.  I think it is important for the students to be able to see the results and especially the comments.  If provides a chance for even more dialogue.

As I  explained yesterday, we started a radial acceleration and force sample problem with the toy airplane. Radial Acceleration Sample 2 is our work from one of the sections: (You’ll notice I worked through it using the ‘Work Backwards’ approach.  This is a hugely powerful problem solving approach for students.)

Here is how I checked the answer using a Vernier laser gate and the Strobe file in Logger Pro.

Here is a screen shot of the file:

So about 4.6% difference.. I’ll take it!

General Physics:

After looking through some of the formative assessment ‘colors’ and comments, I decided to add a day of practice.  To help review and extend the idea of component of a vector I used the pHet simulation called Vectors, here it is. I like this because you can display the components as projections on the x and y axis.  After that there was an additional practice sheet.  The fourth mod class simply worked through it in small groups while I circulated and provided some small group(s) instruction.  With the 7th mod class I played the Mistake game for the first time… I made a few mistakes with it.  I had two groups do the same problems.. a bad idea because as the rest of the class tries to determine the mistake, invariably the correct answer gets discussed.  This is a good thing except when there is another group that has tried to include a subtle mistake in the force diagram yet to be presented.  Another mistake was to not limit the guesses that could be made. I had attempted to make the game into a chance to earn some candy (Smarties) if no one determined the mistake, or if it was determined.  I also handed out Dum-Dums if there was a mistake made that was not intentional.. really interesting that these showed up in the discussion and the presenting group claiming “no that is not a mistake”.

# Days 87-91: Still Trying to Catch up

These days cover the first week of our second semester.  I’m fortunate because I really do not have any new students, because I had them during the first semester.  So here was the week in review:

Monday — I allowed the students to see the problem set from the final exam.  Yep, that’s right, they saw the final exam after it was graded.  I feel assessments should be a learning opportunity and the final should be no different, the students SHOULD get to see the actual exam rather than a number on Infinite Campus.  We also had a brief introduction to our next unit, uniform circular motion.  We discussed the difference between rotating  and revolving.

Tuesday — We continued the discussion from the day before and built the concepts of  ‘angular motion key players’.  When we first started linear motion we talked about the key players; position, time interval, displacement, velocity and acceleration.  We developed all aspects (the conceptual, the graphical and the equations) essentially at the same time.

SIDEBAR: To review the concept of a radian I used a sweet little animated gif I found (possibly on Wikipedia?), here it is.

To accomplish this, I used a ‘mini merry-go-round of physics’ with a dry erase marker on it.  I also used a Vernier Photo gate and the Strobe setting.  I added a few calculated columns so I could display the angular position, and velocity graphs. Here is the set up:

Next time I use this, I am going to use a thin circular piece of wood to make a bigger platform and attach a series of evenly spaced (thin) metal strips to block the gate.  The values displayed will not be the actual angular velocity, but the graphs will be much cleaner.

The angular motion (kinematic) equations were built by the students using the displayed angular motion graphs and the linear motion equations.

We also had the pre-lab discussion for the first experiment, described next.

Wednesday and Thursday: The Tangential Velocity Experiment (shared a bunch of years ago by a former member of the Phox Share Group)

I replaced the marker (that represented a single point on the rotating platform) with my Einstein action figure.  The pre-lab discussion included Albert’s angular velocity and his instantaneous velocity— a linear quantity that is always tangent to the circular path.  We defined this as tangential velocity.  We talked about what might affect the tangential velocity.  Two factors surfaced: angular velocity and the radius of the circular path. So, two parts to the experiment:  Tangential Velocity as a function of Angular Velocity (with a constant radius) and Tangential Velocity as a function of radius (with a constant angular velocity).  Now, you and I know that we would not need to do both parts of the experiment, but the students do not.

Here is a picture of the experimental set-up:

We use two different photo gate files: Strobe (for angular velocities) and One Gate Timing (for tangential velocity). It’s hard to see, but there is a thin metal flag attached to the meter stick with a binder clip.  This is used to trip the gate.

I only have six  really well-functioning ‘mmgrop’ (mini merry go round of physics), so we broke the class in half.  On Wednesday, half gather data for the first part of the experiment while the other half did small group work on some rotational kinematic problems (solving both graphically and with the equations).  Thursday, we simply flip-flopped the groups.  The second data gathering group gathered data on the second part of the experiment.

Friday:  We started the period with a short one problem assessment on solving rotational kinematic problems, then WB’ed the results of the experiment.  I think most of you see that the slope of the linear tangential velocity as a function of the angular velocity graph has units that simplify to meters and represents the constant radius, while the linear tangential velocity as a function of the radius graph slope units simplify to the angular velocity.

General Physics:

With the start of the second semester, we begin dynamics with the general students.  We follow the same basic flow as we did with the Advanced classes.

Monday — The students also were allowed to look through their problem set from the final exam. After this, we gave them the a ‘Forces Diagnostic’ pre-test.  In both of my classes, the average score was about 10 (out of 30).

Tuesday — We discussed forces in a broad sense and then completed the Forces ILD to develop the concept of N3L.

Wednesday — We finished the N3L discussion and practiced identifying N3L pairs with balloon-o-copters.  Note to self– do not buy the cheap version, they work like ….

Thursday — We developed the concept of N1L using the Motion of a Cart with Two Tension forces.  As I wrote about with the Advanced class, this does an excellent job of clearly developing the differences in resulting motion when forces are balanced and when the forces are un-balanced.

Friday — We formalized N1L with several hands-on demos the students completed.

Whew.. all caught up again. Now if I can just stay caught up…..

# Day 57: The Ring of Fire

As explained yesterday, today was spent checking the  Stunt Barbie – Human Cannonball-Ring of Fire predictions.  Why Ring of Fire you ask….  here’s why:

And of course Johnny Cash playing in the background.

General Physics:

Unit 1 (Constant Velocity) Summative Test… hoping for good results.

# Day 53: Group Problem Solving

I was not in school on Friday.  The plan for both the Advanced Physics course and General Physics course was the same; group problem solving.  The Advanced assignment was a set of six projectile problems, while the General assignment was a set of three constant velocity problems that were to be solved graphically.  While I sometimes cringe at using an entire class period on this type of assignment, many of my students love this type of day.It allows them to practice solving problems and get help at the same time. In a sense it is what many of us crave…extras time to work. I suppose it is like a teacher getting an extra prep hour.

# Day 31: The Ramp Lab

As mentioned yesterday, today was all about gathering data for the ‘ramp’ lab.  This is the (usual) experiment that develops several concepts, that I’ll discuss tomorrow. I have set this up a number of different ways.  This year I gave the students much more freedom and choice that I have in the past.  They could choose from 3 different objects to send down the ramp.  Their choices were a hot wheels car on its track, a constant acceleration dune buggy (this is the pull back kind, but they free wheel if you do not wind them up), or a large steel marble on a channel made from physics (duck) taping to 10 foot pieces of conduit together.  These are the same pieces of conduit I use a guard rails for our buggy bash.  I like the conduit ramps because it really nicely extend the ramp so the students can get more data, and allows for shallow angles to make the data easier to gate.

In a sense, we repeated the position vs. time experiment we did in the cv unit.

SIDEBAR: When we introduce the lab, it is not one of the ‘does the cv model still work in this situation” intro’s.  I do not do this because I have found the majority of my students already know the cv model will not apply.

I like the similarities because we are still measuring positions and times to describe the motion.  The students were also able to choose a method of timing; stopwatches or photogates (Pulse Timer – Two Photogates).  It totally blows me away that after all we have talked about in terms of our inability to make accurate time measurements by hand, some groups still reach for the stopwatches first.  Maybe it’s because they know them or think it is easier.  The only condition I set is this:  the odds groups (I use playing cards to group my students into lab grops) will put the origin or ‘0’ at the bottom of the ramp and start at some initial positive position, while the evens will put ‘0’ at the top and roll in the positive direction.  I love this when it comes to whiteboarding tomorrow.  It allows me to see who is still stuck on distance travelled instead of position and it awesome when they try to explain the meaning of the slope of the linear graph… stay tuned….

General Physics:

Lens and refraction test today… nothing too exciting.  Tomorrow we start in on reflection and plane mirrors.