Make a light bulb with pencil lead

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.

After entering the experimental data in the table, you should automatically see them being plotted in the graph window. As a good scientific habit, you always want to show only collected data points without the line in between them. Let's get one more point. Now let's adjust 10 volts-- no 20 volts. Let's see can we do exactly 20? Yeah, here's 20 volts. And my voltage is 19.42, and 0.06 ampere. Go Logger Pro, enter this data. 19.42, current is 0.06.

After entering the experimental data in a table, you should automatically see them being plotted in a graph window. As a good scientific habit, you always want to show only the collected data points, without the line in between them. Just show only the

data points without the line between them. So double-click on the graph window, and check the option Connect Points. Uncheck this Connect Points option and click that. You will see only the data on your graph window.

After getting all the data, apply linear feed to your set of data. Double-click on the small window with the feed parameters and select Show Uncertainty. From the slope, calculate the resistance of the virtual pencil. Propagate the uncertainty in the slope into the uncertainty in the experimental resistance of pencil.

Then follow the instruction provided in lab manual to rescale the whole graph window to about half of the available screen space. You can rescale the graph without covering the data table. Just be sure you have data table available, and make your graph half over to your screen. Insert second graph, displaying the resistance calculated in third column on both axes of the new graph. Now insert new graph.

With the resistance calculated on both axes. Resistance should be on the y-axis and on the x-axis. Again uncheck the Connect Points option, rescale this graph window to fit into space remaining on the page. By dragging around with the mouse, select all data points of this plot and apply statistics. When you get all of your data points select all the data points by dragging them with the mouse and select Statistics. I click on Statistics button here. Or you can get it from Analyze menu. We can go Analyze and get Statistics from here or from there. Save the logger profile for your future reference.

How does the mean value displayed in the statistics window-- when you get statistics you see the mean value of the resistance. How does that mean value compare to the resistance computed from the slope of the first graph? From the slope of the first graph, you will calculate the resistance from there and compare the mean value of the resistance from the second graph. Start to measure the resistance of the virtual pencil lead, along with its uncertainty. Capture the screen with the Logger profile, and paste it into a Word file, and attach it to your lab report.

If you assume that the virtual pencil lead was made out of material of resistivity rho equals 3.5 times 10 to the negative 4 ohm times meter. Which is not pure graphite, it is composition of graphite.

And the diameter of the lead was 0.6 millimeter. How long was the pencil? You need to consider rho is given, the diameter is given. You need to calculate-- from your experiment you are measuring the resistance-- you need to calculate the length of the pencil lead.

Part two. Investigating resistive properties of a light bulb. KET Virtual Physics Lab using your username and password. Just follow the link in your lab manual. Log in. Click the labs and select lab 16, DC circuits. Before running simulation, read the full description and detailed information. Here is DC circuit, run this lab now.

Connect the circuit shown below. In your diagram, you'll see there is battery, switch, ohmmeter, light bulb, and voltmeter. Pay attention that ohmmeter is connected with the light bulb in series and the voltmeter is connected to the light bulb in parallel. And the switch is open.

Let's start building the-- connecting the circuit. We need the battery. We need wires. One more wire. Switch. Let's put one more wire and then ohmmeter. Where is-- there is my ohmmeter. OK, one more wire. Then we will go-- a second wire, I have to rotate this here. And get the light bulb. As you can see in your picture. And then you go just one more wire here. One long wire to the other end and complete the circuit by touching here.

Now we need to connect our voltmeter. That is my voltmeter let's put one wire here. I can put here the voltmeter. Let's make it exactly what you see on the lab manual. And complete this part. We built the circuit shown there. Please note the ohmmeter now is connected in series, and the voltmeter is connected in parallel to the light bulb. If you close the switch you will measure the current in your circuit by ohmmeter and they will measure the voltage drop on light bulb.

Click on the battery and adjust the voltage to be one volt. Just use this arrow, or you can highlight and type one volt. Double-click the switch to close the circuit. Now you see the current is 0.09 amperes and voltage drop on light bulb is 1 volt.

Open a new file in Logger Pro and record first pair of data. The voltage across the light bulb as measured by the volt meter and the current displayed by the ohmmeter. Again you need to label

the first column like voltage. Unit, short name volt, unit volt. And so on. Same way, you will rename the second column current in unit ampere. Enter the numbers you can read from here. Current is 0.09 ampere and voltage is 1 volt. Remember to label the column heading appropriately and enter the unit.

Since the internal resistance of ohmmeter is negligible, there is no potential drop across the instrument, and the voltage across the light bulb equals the output voltage from the battery. You see my output voltage from the battery was 1 volt, and voltage drop on light bulb is also 1 volt, because internal resistance of ohmmeter is negligible. There is no voltage drop on ohmmeter. All the voltage from the battery will be dropped on light bulb.

Next, open the switch. Double-click on switch to open it. Change battery output signal to 2 volts. Now we need to double-click here and adjust the voltage to 2 volts. Close the switch again back, double click on it and read the values of the current and the voltage.

I enter these data in Logger Pro. Take these readings and enter into Logger Pro. Open the switch, and repeat the same procedure for the following voltages from the battery. 4 volt, 6 volt, and so on. You see the voltages in your lab manual. And read corresponding current. Read the data and enter this data into Logger Pro. Then add the new calculated column as you did before to the data table, showing the resistance of the light bulb, expressed in ohms. As determined from the Ohm's law, resistance will be called voltage divide current.

Now assuming the filament of the light bulb is made of the tungsten, for which temperature coefficient of resistivity is given, it's alpha equals 4.5 times 10 to the negative 3 one over Celsius. And the resistance of light bulb at room temperature, temperature t naught equals 20 Celsius equals to 10 ohm. Create yet another calculated column displaying the temperature of light bulb. In Logger Pro, you need to create two calculated column. The first one was the resistance. Now you can create another calculated column-- new calculated column which will be temperature in Celsius.

The equation. You have to type the equation. To type the equation, you need to use the equation five from your lab manual, and

rearrange equation five to get direct relationship of temperature versus resistance. Insert a new graph showing filament temperature versus the resistance. Resize both graph windows I versus V and temperature versus R so they nicely fit on one page, along with the data table. Always be sure that rearrange the graphs of these windows to have both on one page. This was first one and second one on the bottom, and show the data table for both of them. Rearrange everything.

Based on the graph current versus voltage for the light bulb, what can you calculate? Is the light bulb an ohmic or non-ohmic circuit element? When you will get graph, you will see it. If the graph is linear, that means your element is ohmic. If the graph is nonlinear than it is non-ohmic element. For the ohmic element the resistance must be constant.

Finally, calculate the ratio of the resistance of the light bulb at 60 volt to its resistance at 1 volt. You'll get the resistance at 60 volt and one volt. Then you have to get the ratio of these resistances. Also compute the similar ratio for the corresponding bulb temperatures at 1 volt and 60 volts. Which parameter, the filament resistance or it's temperature was increasing with a faster rate? After calculating, you can answer all these questions. Capture the screen with the Logger Pro file and paste it into a Microsoft Word and attach it in your lab report. Thank you.