Physics Activity
Series & Parallel Circuits
Purpose:
- to practice constructing electric circuits
- to observe characteristics of series and parallel
circuits
Discussion:
In this lab activity, you will construct a sequence of simple
series and parallel circuits using small light bulbs.
Equipment:
1.5/2 VDC power supply
|
3 light bulbs & sockets
|
7 connecting wires
|
1 knife switch
|
Procedure:
IMPORTANT: In this lab
activity you will use ONLY the "COMMON" and "1.5/2
VDC" terminals on the power supply. Connecting the circuit to any
other terminals will certainly result in destruction of equipment
and might well be hazardous to you and your lab partner. This will
NOT be treated as a "harmless prank". Disciplinary
action will be taken, and you will be responsible for damaged
equipment.
Preliminaries:
- Set
up the circuit depicted in the schematic diagram shown at right
using the power supply, switch, one light bulb, and 3 wires. Since
you are probably not comfortable reading an electrical schematic,
here's how:
- Clip one end of a connecting wire to the 1.5/2 VDC
terminal of the power supply.
- Connect the other end of the wire to either side of the
knife switch.
- Be sure that the switch is open.
- Using another wire, connect the other side of the switch to
either screw on the light socket
- Connect the third wire from the other screw on the light
socket to the COMMON terminal of the power supply.
- Close the switch. If the light bulb doesn't light, check your
connections. If you can't get it to work, call your teacher.
Series Circuits:
- Open
the switch. If the light doesn't go out, check your connections.
If you can't figure it out, call your teacher.
- Connect another light bulb in series with the
first. To do this:
- Be sure the knife switch is open.
- Disconnect the wire at the COMMON terminal (only) and
connect this end to either screw on the new light socket.
- Connect a new wire from the other screw on the light socket
to the COMMON terminal on the power supply.
- Close the switch. How does the brightness of the two light
bulbs in series compare with the brightness of the single light
bulb?
- Unscrew one light bulb. What happens?
- Add a third light bulb in series with the first two. (Follow
instructions in step 4.)
- Compare the brightness of the three bulbs in series to the
brightness of the original light bulb.
- Unscrew one of the bulbs. What happens? Does it make any
difference which bulb you remove?
Parallel Circuits:
- Remove
three light bulbs from your circuit so that you have the original
circuit from step 1 and 2 (a switch plus one bulb).
- Connect a second bulb in parallel with the
first. To do this:
- Be sure the knife switch is open.
- Connect a new wire from a screw on the original light
socket to either screw on the new light socket.
- Connect a new wire from the other screw on the original
light socket to the other screw on the new light socket.
- Close the switch. How does the brightness of the two light
bulbs in parallel compare with the brightness of the single light
bulb? How does it compare with the brightness of the two
bulbs in series?
- Unscrew one light bulb. What happens?
- Add a third light bulb in parallel with the first two. (Follow
instructions in step 2.)
- Compare the brightness of the three bulbs in parallel to the
brightness of the original light bulb, and to the brightness of
the three bulbs in series.
- Unscrew one of the bulbs. What happens? Does it make any
difference which bulb you remove?
- "It says in the book" that two light bulbs in parallel are
just as bright as a single light bulb, but that probably didn't
happen, did it? What are some plausible hypotheses for this
discrepancy?
last update March 23, 2001 by JL
Stanbrough