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DC Circuits I - Ohm's Law

Lab Experiment

Hello. Today we will do-- this is Circuit One: Ohm's Law, using the PhET and KET websites. All the lab will be simulation from this site. The objective of the lab: Apply Ohm's law to find the resistance of the virtual pencil lead, the first part of the experiment. And the second part of the experiment, investigate the behavior of light bulb in a simple DC circuit.

Part One. Procedure. Determining the resistance of pencil lead. The Ohm's law can be used to find electrical properties, namely the resistance of any conductor. In this part of the experiment, you will apply the Ohm's law to determine the resistance of virtual pencil lead. You will measure the current through the pencil lead and the voltage drop across this element for a few output voltages, delivered by battery. Next you will present that data graphically, plotting I pencil versus V pencil, current through the pencil versus voltage drop on the pencil, and analyze the plot to find the resistance of the simulated pencil.

Now open up the PhET interactive simulation website. You have a link in your lab manual. Control-click on that link and open this page. Download construction kit DC only. You can download this. Instead of downloading I can run it. I am using different computer. Open the experiment.

Using the circuit components from the right tool menus and the grab bag options, that is where you find the pencil lead. Construct a circuit similar to the one shown in figure 2 in your lab manual.

Let's start. We need battery. Bring your battery over here, putting the way which you see in your lab manual. Then use wires. Rotate, clicking on the ends and make it straight. You can put another wire here and make it shorter. Now we can put switch. And one more wire after the switch. Put ohmmeter, just clicking, marking the box of ohmmeter. You'll get ohmmeter here, then move the ohmmeter in your circuit. Touch in your circuit another wire more. Let's put one more wire here, rotate from this end. You can make it longer. Now we need to put one more short wire to keep us

seeing your circuit, in your figure 2, in your lab manual. Now we need to get that pencil lead. OK, pencil lead attached and then this way. And finally, you we can use the last wire to close the circuit.

OK, we have our circuit is built, now we need to have volt meter to measure the voltage drop on the pencil lead. Just keep polarity as you can see in your figure, the red one must be on the high potential side, and black one on low potential side of the pencil lead.

Please note that ohmmeter is connected in series with the pencil while the voltmeter-- ohmmeter is connected in series-- while the voltmeter is connected with the pencil in parallel. The red lead of the ohmmeter ties the pencil end of the high potential, and black end is connected to the end of lower potential. This is high potential end of the pencil, this is low potential end of the pencil. Potential is highest at this point, it is dropping this way, until you get here, you get zero potential.

Right-click on the battery allows you to select the Voltage Change option, which opens the voltage section windows as you can see in your figure in your lab manual. Right-click on battery and change the voltage. You can move this slider to adjust the voltage of your battery. We will leave this here. By adding the internal resistance of battery we will make this circuit [? sharing ?] even more lifelike. Right-click on battery again, and change its internal resistance to 9. Change internal resistance and adjust internal resistance to 9 ohm.

Apply 5 different voltages from the battery, ranging from 0 to 100 volts. Let's try to adjust from 0 to 100, we'll try to adjust these voltages evenly spread. I see I can easily put 10. Let's go 10, 20, 30, and so on. After adjusting the battery voltage to the desired value, close the switch and record the current measured by ohmmeter and the voltage detected by voltmeter. Already we have adjusted the voltage on the battery. We have ohmmeter in circuit, connected in series, voltmeter is connected in parallel of pencil lead, but we don't have still any current of the voltage drop is 0, because circuit is open. Now if I close the circuit, you will see the value of the current, and the voltage drop on the pencil.

Record this data. You have 0.03 amps current, and voltage drop on pencil is 9.75. At the voltage 10 volt from the battery and internal resistance of the battery is 9 ohm.

Now you can open Logger program and enter your data. This program you can find My Application on My ASU side. The default screen, as you can see, it contains two columns, x and y. Enter V pencil, voltage on pencil data, expressed in volts.

In the first column, then you can double click on the name. This is voltage, so then you can put voltage, and unit is volts also. The second one would be our current. Short name is I, and unit is ampere. And to enter your data, which you will read from the side, voltage drop on the-- Oh. I made a mistake. I should enter the voltage is not 10 volts, but 9 point-- whatever you read from there. It's 9.71. And the current was-- you go 0.03 amps. And so, we labeled the columns; voltage current. And you need to enter the data which you will collect during the experiment.

Create new calculated column for the resistance R, expressed in ohms. You go data, new calculated column. Column name is resistance, short name R, units ohms. And create an expression where you have-- that will be the voltage divide current, done. Double-click the heading of the column to change its name and so on, and enter the unit for the type in data and select the number of decimal places you wish to display. Double-click the heading of each column, and select the number of decimal places you wish to display. Decimal places I can select here for example, two decimal places, or three decimals places you want to keep.