Hello and welcome. Today I'd like to take a look at Ohm's Law.
The write-up for this lab comes from our Physics through Inquiry manual.
To do the lab, we're going to need a few things.
We're going to need an interface.
We're going to need a Voltage-Current Sensor.
We're using a Charge/Discharge board and an assortment of patch cords to put it all together.
So, let's do that.
I'm going to go ahead and connect my Voltage-Current Sensor to my interface.
And then I'm going to connect the voltage across the component that we're first interested
in, and that's the 10 Ohm resistor on the board.
So, we'll go ahead and put that in place.
And then I'm going to be connecting in the switch here, which I'm going to put into the
neutral position, so that I don't have a complete circuit yet.
And what I want to do is connect the positive side of the battery to the positive side of
the Charge/Discharge switch.
I'm going to connect the negative side of my circuit to the negative side of my battery.
And then I'm going to connect the negative side of my capacitor to the top of my resistor.
OK, so the only thing that remains to connect is the current sensor, because we're also
looking at current at the same time.
To do that, I'm going to go ahead and connect the negative side of my current sensor to
the positive side of my capacitor.
And the positive side of my current sensor to the middle of my switch here. OK.
So, as you can see, once it comes together, it's a little bit like spaghetti.
So it's nice to go through and do it one piece at a time and discuss with your students as
you're going what they're supposed to be doing, like, observing the voltage across a component,
or the current through the circuit.
So, we're ready to go here.
I'm going to go ahead and flip the switch into the charge position, and that's going
to charge up my capacitor.
That's going to be the power supply for our circuit and, as it discharges, that voltage
will change.
One of the reasons we do this lab this way is so the students can see that Ohm's Law,
in this case, applies in a circuit where the voltage and current are continuously changing.
Up until this point, they may have been doing labs where they're measuring discrete components
and discrete voltages and currents in a static system.
So, we wanted to do something that had some change in it.
So, the set up is very simple.
I'm going to go ahead and bring up Voltage, using the Show path on my SPARK Science Learning
System.
And that gives me a Voltage versus Time graph. I'm going to change the axis from Time to
Current.
That's going to give me a Voltage versus Current graph.
And that's what we're interested in seeing.
So, I want to see how these things change together.
I'm going to go ahead and put my switch back into the neutral position, and I'm going to
start discharging, and then I'm going to start collecting data.
And immediately you're going to see a graph of Voltage versus Current evolve over time.
It's going to start heading towards zero, of course, because it's discharging.
And as it gets close to zero, we're going to go ahead and stop collecting data.
It will start slowing down a little bit as it starts getting closer to zero.
I'll hit Stop here.
And then the analysis is relatively simple.
I'm going to go ahead and bring up a linear fit for this particular graph, because I'm
interested in the slope of that line.
And, sure enough, I get a slope of 9.92, very close to the 10 Ohms of the resistor, and
well within the tolerance of that particular resistor.
So, excellent results.
To continue this lab, I'd go ahead and look at the same thing on a 33 Ohm resistor, and
then also on a light bulb to compare ohmic versus non-ohmic behavior.
As you can see, relatively quick to set up. Good graph.
We also have a SPARKlab for this lab on the device here.
So, whether you're using the paper manual or the SPARKlab, it proceeds in very much
the same way.
We hope you enjoy doing this with your students, and don't forget to practice safe science.
Thank you.