Download Procedure for Part A: Simple Circuit

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Name: __________________
Partner: __________________
Date: __________________
Lab Activity: Measuring Voltage and Current in a Simple Circuit
Materials:
 9V battery
 2 light bulbs
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1 voltmeter
1 ammeter
 8 wires
Procedure for Part A: Simple Circuit
1. Before building your circuit, measure the voltage across the battery. To do this, connect the negative
terminal of the battery to the black negative terminal of the voltmeter. Connect the positive terminal
of the battery to the red positive terminal of the voltmeter (use the 15V scale throughout this lab
activity). Since you are using the same battery throughout this activity, record the voltage at the
source in Tables 1, 2, and 3. Disconnect the voltmeter from the battery.
2. Build a simple circuit as follows:
 Connect the negative terminal of the battery to the black negative terminal of ammeter.
 Connect positive red terminal of ammeter (use the 500mA scale throughout this lab activity) to
a light bulb (attach to screw)
 Connect other side of light bulb (other screw) to a switch.
 Connect the switch back to the positive terminal of the battery.
3. Close the switch. Note the brightness of the bulb. Is it very bright, bright, dim, or very dim?
4. Read the ammeter, and record the current of this circuit in Table 1. Be careful you read the scale
correctly!
5. Connect the voltmeter across the light bulb to measure voltage drop. Make sure the negative terminal
of the voltmeter is connected to the more negative end of the light bulb (and positive to positive).
Record voltage drop in Table 1.
6. Open the switch. Draw a circuit diagram of this circuit in the box below Table 1. Include the voltmeter
and ammeter in your diagram. LEAVE THIS CIRCUIT INTACT WHEN MOVING ON TO PART B.
Observations for Part A:
Brightness of Bulb: _____________________________________
Table 1: Current and Voltage for a Simple Circuit
Voltage at Source (V)
Circuit Diagram:
Current (mA)
Voltage Drop at Bulb (V)
Procedure for Part B: Series Circuit
1. Add a second bulb to the simple circuit in Part A by connecting it in series (connect it between the
first bulb and the switch).
2. Close the switch. Note the brightness of the bulbs. Are the bulbs brighter, dimmer or the same
brightness compared to when there was only one bulb?
3. Read the ammeter, and record the current of this circuit in Table 2. Since this circuit has only one
path, the current will be the same at every point in this circuit.
4. Connect the voltmeter across the first light bulb to measure voltage drop. Repeat for the second
light bulb. Record your values in Table 2.
5. With switch closed, unscrew one bulb. Record your observations then screw the bulb back down.
6. Open the switch. Draw a circuit diagram of this circuit in the box below Table 1. Include one
ammeter and one voltmeter in your diagram.
Observations for Part B:
Brightness of bulbs: ________________________________________________________________
What happens when one bulb is unscrewed? ___________________________________________
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Table 2: Current and Voltage for a Simple Circuit
Voltage at Source (V)
Current (mA)
Voltage Drop at Bulb 1 (V)
Voltage Drop at Bulb 2 (V)
Circuit Diagram:
Procedure for Part C: Parallel Circuit
1. Remove the second bulb from your circuit, and reconnect the first bulb to the switch so you have
the simple circuit you built in Part A.
2. Add the second bulb in parallel with the first bulb.
3. Close the switch. Note the brightness of the bulbs. Are the bulbs brighter, dimmer or the same
brightness compared to when there was only one bulb?
4. Read the ammeter, and record the current at the source in Table 3.
5. Disconnect the ammeter (connect the battery directly to the first bulb). Connect the ammeter
along the path of the second light bulb. Record the current at bulb 2 in Table 3.
6. Connect the voltmeter across the second light bulb to measure voltage drop. Record in Table 3.
7. With switch closed, unscrew one bulb. Record your observations then screw the bulb back down.
8. Open the switch. Draw a circuit diagram of this circuit in the box below Table 3 (include meters).
Observations for Part C:
Brightness of bulbs: _____________________________________
What happens when one bulb is unscrewed? ___________________________________________
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Table 3: Current and Voltage for a Simple Circuit
Voltage at Source (V)
Current at Source (mA)
Current at Bulb 2 (mA)
Voltage Drop at Bulb 2 (V)
Circuit Diagram:
Discussion Questions (please answer in complete sentences):
1.
a) In Part A, how did the voltage at the source compare to the voltage drop at the bulb?
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b) In this circuit, what energy conversion is occurring at the load?
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2. a) Compare the current in Part A (see Table 1) to the current in Part B (see Table 2). How does
adding a second bulb in series affect the current in the circuit?
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b) Why does adding another load in series affect the current in this way?
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3. a) Compare the voltage drop across the bulb in Part A (see Table 1) to the voltage drop across the
bulbs in Part B (see Table 2). How does adding a second bulb in series affect the voltage drop
across each load?
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b) Why does adding another load in series affect voltage drop in this way?
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4. Is there a relationship between voltage drop and brightness of a bulb? Explain.
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5. a) Compare the current in Part A (see Table 1) to the current at the source in Part C (see Table 3).
How does adding a second bulb in parallel affect the current coming from the source?
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b) Why does adding another load in parallel affect the current in this way?
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6. In Part C (parallel circuit), how does the current going through the second bulb compare to the
current at the source? Explain your observations.
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7. Consider this statement: “Under ideal conditions, the voltage drop across each bulb in a parallel
circuit should equal the voltage at the source.”
a) Based on your knowledge of parallel circuits, explain why the statement makes sense.
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b) Describe whether or not your results support the statement above (see Table 3). If not, why do
you think your results are different?
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