Light Bulbs in parallel and in series - Newman Physics



Phet Simulation: Series and Parallel Circuits 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 ; 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 |Bulb 2 |Total(Battery) |

|Potential Difference (V) | | | |

|Current (A) | | | |

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.

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