Resistances In Series And Parallel Circuits
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Austin E. Barnett Bogan High School
3939 West 79th Street
Chicago IL 60652
1. To observe the difference in illumination for a given set of bulbs when
placed in series and in parallel circuits.
2. To calculate the IR drop across a network of resistances in series and
Six flashlight bulbs and sockets, one switch for each of the two circuits, four
"D" cells, masking tape, twenty 10-cm pieces of bell wire, two DC ammeters of
range zero amp. to one amp., two DC voltmeters of range zero volts to five
Activity 1. Series Circuit
1. Connect three bulbs in sockets in series with a switch, an ammeter, and
two "D" cells that are firmly taped together top to bottom. Place the
ammeter between the switch and the two-cell battery. Connect the negative
terminal of the ammeter to the negative terminal of the battery.
2. Close the switch. Read and record the amount of current. Open the switch.
3. Reconnect the ammeter between two of the bulbs. Close the switch. Read and
record the amount of current. Open the switch.
4. Reconnect the ammeter as in step one.
5. Connect a voltmeter across one of the bulbs. Be sure that the negative
terminal of the voltmeter is connected toward the negative terminal of the
6. Close the switch. Read and record the voltage drop. Open the switch.
7. Repeat steps 5 and 6 with the voltmeter connected across two bulbs.
8. Predict what will happen to the voltage drop if the voltmeter is connected
across all three bulbs. Repeat steps 5 and 6 with the voltmeter connected
across all three bulbs.
9. Remove one of the bulbs from its socket without disconnecting the socket.
Remove the voltmeter. Close the switch. Record the ammeter reading. Open
10. Reconnect the circuit, so that, there are only two bulbs, and sockets in
series with the ammeter, switch, and battery. Record the current value and
voltage (IR) drop across the circuit. Open the switch.
Students, this concludes our first activity. Now, let's discuss what took
Activity 2. Parallel Circuits
Students, the purpose of this activity is to study the properties of a parallel
1. Connect three flashlight bulbs in parallel sockets.
2. Connect 2 "D" cell batteries, a switch, and an ammeter in series. Place
this in parallel with the 3 sockets. Be sure, that the negative terminal of
the ammeter is toward the negative terminal of the battery.
3. Close the switch. Read and record the current value. Notice how bright
the bulbs are. Open the switch.
4. Without disconnecting the socket, remove one bulb. Close the switch.
Record the current value. Compare the brightness of the remaining bulbs to
their brightness before. Open the switch. Replace the bulb.
5. Reconnect the ammeter in series with one of the bulbs. Predict how the
current will compare to the previous reading.
6. Test your prediction by closing the switch. Record the current and open
7. Remove a bulb in a different branch from the ammeter. Close the switch.
Read and record the current value. Open the switch.
8. Connect a voltmeter across one socket. Close the switch. Read the meter,
and record the voltage. Open the switch. Repeat for each of the other
Modern Physics Holt: Rinehart and Winston (1990)
Physics: Principles and Problems (1982)