```Resistances In Series And Parallel CircuitsAustin E. Barnett              Bogan High School                               3939 West 79th Street                               Chicago IL 60652                               (312) 536-2180 Objectives:

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
parallel.

Materials:

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
volts.

Strategies:

Activity 1.  Series Circuit1.  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     battery. 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     the switch.  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 place. Activity 2.  Parallel CircuitsStudents, the purpose of this activity is to study the properties of a parallel circuit. 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    the switch.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     sockets. References:

Modern Physics  Holt: Rinehart and Winston (1990)    Physics: Principles and Problems (1982)```