Download Light Bulbs in parallel and in series

Phet Simulation: Series and Parallel Circuits
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Name_______________________________Date________
In this experiment you will see how voltage and current change when bulbs are connected in series and
parallel.
You will also investigate the role of batteries in a circuit.
Light bulbs are primarily used in this experiment instead of resistors because the brightness of the bulb
provides a visual representation of the current through the filament.
Procedure
Go to http://phet.colorado.edu/; search for and open the Circuit Construction Kit.
Light Bulbs in Series
1. Drag and drop one light bulb and one battery in the work area. Drag and drop wires to connect the
battery to the light bulb. Once the circuit is completed, the bulb should light and you should see the
flow of charge from positive to negative end of the battery through the circuit. This is circuit 1.
2. Use a voltmeter (check the box next to voltmeter on the right side of the display) to measure the voltage
across the bulb. Use the non-contact ammeter to measure the current in the wires. Use Ohm’s Law
(V=IR) to Calculate the resistance of the bulb. Circuit 1. Two bulbs in series
Bulb
Total(Battery)
Potential Difference (V)
Current (A)
Calculate R:
3. Right click on the light bulb and check “show value” box. Does this agree with your calculations? ____
Value shown for R= ______ (If it doesn’t agree, go back to step 2 and find your calculation error.)
4. Set up another circuit with one battery and two light bulbs connected in series (everything is in one
single loop). This is circuit 2. Use the voltmeter and the non-contact ammeter to measure the values
listed below.
Circuit 2. Two bulbs in series
Bulb 1
Bulb 2
Total(Battery)
Potential Difference (V)
Current (A)
5. Show that V1 + V2 = VT These stand for voltage across bulb 1, voltage across bulb 2, and the total
voltage across the battery.
6. The currents are all ( the same / different ).
7. Using ohm’s law, calculate the resistance of Bulb 1 (R1), resistance of Bulb 2 (R2), and the total
resistance (RT). Show your work!
8.
Show that R1 + R2 = RT
9. Set up another circuit with three bulbs in series. This is circuit 3. Use the voltmeter and the non-contact
ammeter to measure the values listed below.
Circuit 3. Three bulbs in series
Bulb 1
Bulb 2
Bulb 3
Total(Battery)
Potential Difference
(V)
Current (A)
10. What relationship can you make for voltage? Write an equation that uses V1, V2, V3 and VT.
11. The currents are all ( the same / different ).
12. Calculate the resistance of Bulb 1 (R1), resistance of Bulb 2 (R2), resistance of Bulb 3 (R3), and the total
resistance (RT).
13. What relationship can you make for resistance? Write an equation that uses R1, R2, R3 and RT.
14. As you add more bulbs in series, the brightness ( increases / decreases / stays the same).
15. As you add more bulbs in series, the total resistance ( increases / decreases / stays the same).
16. As you add more bulbs in series, the current ( increases / decreases / stays the same).
17. As you add more bulbs in series, the voltage ( increases / decreases / stays the same).
When finished, remove circuits 2 and 3 (select each item, right click, then remove). Keep circuit 1.
Light Bulbs in Parallel
18. Set up a second circuit with one battery and two bulbs in parallel as shown. This is
circuit 4. Use the voltmeter and the non-contact ammeter to measure the values listed
below.
Circuit 4. Two bulbs in parallel
Bulb 1
Potential Difference
(V)
Current (A)
Bulb 2
Total(Battery)
19. Notice that the current coming from the battery splits. Some of it goes to bulb 1 and the rest goes to
bulb 2. What relationship can you make for current? Write an equation that uses I1, I2, and IT.
20. The potential differences are all ( the same / different ).
21. Calculate the resistance of Bulb 1 (R1), resistance of Bulb 2 (R2), and the total resistance.
22. Do the resistances follow the resistance equation (R1 + R2 = RT) from series circuits? _____Plug in your
values below to support your answer.
23. Set up another circuit with three bulbs in parallel as shown below. This is circuit 5. Use
the voltmeter and the non-contact ammeter to measure the values listed below.
Circuit 5. Three bulbs in series
Bulb 1
Bulb 2
Bulb 3
Total(Battery)
Potential Difference
(V)
Current (A)
24. What relationship can you make for current? Write an equation that uses I1, I2, I3, and IT.
25. The potential differences are all ( the same / different ).
26. Calculate the resistance of Bulb 1 (R1), resistance of Bulb 2 (R2), resistance of Bulb 2 (R3) and the total
resistance.
27. Do the resistances follow the resistance equation (R1 + R2 + R3 = RT) from series circuits? _____Plug in
your values below to support your answer.
28. As you add more bulbs in parallel, the brightness ( increases / decreases / stays the same).
29. As you add more bulbs in parallel, the total resistance ( increases / decreases / stays the same).
30. As you add more bulbs in parallel, the current ( increases / decreases / stays the same).
31. As you add more bulbs in parallel, the voltage ( increases / decreases / stays the same).
The Role Of Batteries In A Circuit
Clear the screen then set up the following circuits:
 Circuit 1 – One light bulb connected to one battery.
 Circuit 2 – One light bulb connected to two batteries. Batteries should be connected in series, so that
the positive end of one is connected to the negative end of the other one.
 Circuit 3 – One light bulb connected to three batteries. Put the batteries in series.
Notice the brightness of the bulbs and the rate of flow of charge in the circuits as more batteries are added.
Use the voltmeter and the non-contact ammeter to measure the voltage across each bulb and the current through
it. Record your results below.
Adding more batteries to a light bulb
Current through the bulb
Voltage across the bulb
Calculated Resistance
Circuit 1 -One battery
Circuit 2 - Two
batteries
Circuit 3 - Three
batteries
32. Calculate the resistance for each circuit and add it into the table above.
33. As you add more batteries, the brightness ( increases / decreases / stays the same).
34. As you add more batteries, the total resistance ( increases / decreases / stays the same).
35. As you add more batteries, the current ( increases / decreases / stays the same).
36. As you add more batteries, the voltage ( increases / decreases / stays the same).
37. Where does the charge flowing in a circuit come from? What is your evidence?
EXTRA:
Build a circuit using 3 items from the grab bag, 3 resistors, and one light bulb. You want to maximize
the current through your light bulb. Draw your circuit below, labeling (1) the battery voltage, (2) the
resistor’s resistance, and (3) the maximum current running through the bulb.