Part One: Properties of Electric Circuits
Exploration 1: Light the bulb
Most of us have heard the word “circuit,” but few of us have a clear idea
of what it actually represents. In this section we will develop a model - an idea
in our minds - of what we mean by the word circuit.
Equipment:
1 round bulb (1.5 V)
1 connecting wire
1 D battery
Part A: Light the bulb!
Using only the single wire and the battery, light the small bulb
Draw the arrangement that you used to light the bulb, below. Be specific about
which parts of the bulb and battery you touched with the wire:
Part B: How charged particles travel
Equipment:
Battery pack with 2 D
batteries
Connecting wires (leads)
2 round bulbs, one in a
base
Empty bulb base
1 large light bulb (for
observation only)
empty
base
The circuit used in Exploration 1 can be thought of as a testing circuit for
determining the existence of a conducting path in the wires, because the bulb
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Part One: Properties of Electric Circuits
glowed. This test will help us determine if there is a conducting path through
the bulb itself.
Set up the circuit shown above. Complete the circuit using the empty
base. Attach the light bulb to the positive terminal and the empty base to the
negative terminal. Does the bulb light?_________
Maybe it is not hooked up correctly. Switch the leads. Attach the light
bulb to the negative terminal and the empty base to the positive terminal. Did
the bulb light? Why or why not?
Put the bulb into the empty socket. Describe what happens:
Switch the leads again, so the original bulb is attached to the positive terminal
and the “new” bulb to the negative terminal. Does it make any difference?
Draw a diagram that clearly illustrates the conducting path through the bulb.
Examine the larger light bulb. Two wires extend from the filament of the bulb
into the base. Note that there is a metal tip, separated by an insulating material
from the rest of the base. Based on your experiments, above, draw a diagram
of the light bulb, showing where the wires attach.
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Part Two: Origin and Movement of Charge
Exploration 2: Schematics
Before continuing in our investigations of electric circuits we need to
develop a “shorthand notation” for electrical elements. Schematics are a
shortcut method of showing how the circuit elements are to be connected.
Schematics of circuits are always shown in technical manuals and other
materials including textbooks. The diagram below compares the pictorial
diagram or real world representation of the circuit you built in Exploration 1 with
the schematic, or physics representation, of the same circuit. Can you identify
the symbols used for each of the elements in the circuit?
To be able to read or draw a schematic you will need knowledge of what
symbols are used to represent the various elements in an electric circuit. These
symbols are fairly universal – a schematic drawn in Asia will look the same as a
schematic drawn in the US, as long as the circuits are the same. The table
below shows some of the basic schematic symbols used in this module.
capacitor
Long line is
positive
Part Two: The Source and Movement of Charge
Exploration 3: Detecting Activity in Wires
Is anything happening in the connecting wires when a circuit is
completed? We are going to use a magnetic compass, the type used to
determine geographic directions, as a tool to help us answer the question just
posed.
Equipment
2 sockets
2 identical round bulbs
Connecting wires
Battery Pack
2 batteries
Liquid-filled compass
Masking tape to tape down compass
1.
Construct the circuit shown in the figure above, except leave one of the
wires to the battery disconnected while you place a compass under the
middle connecting wire (the wire between the two bulbs). Keep the
compass away from any metal such as table legs and the battery cells.
Tape the compass to the table, so it won’t move.
2.
Orient the connecting wire above the compass so that it is parallel to the
compass needle. The compass needle and wire will be oriented in a
north/south direction. For consistency in observations between different
groups in the class, make sure that the compass needle points toward
the positive end of the battery pack, as seen in the diagram. One person
should hold the wire to make sure it remains parallel to the needle and
rests on the top of the compass case. Does the wire seem to have an
effect on the compass needle while the circuit is not connected?
_________________________________________________________
_________________________________________________________
3.
Observe the effect on the compass needle as the final wire is connected
to complete the circuit. What happens?
_________________________________________________________
_________________________________________________________
_________________________________________________________
________________________________________________________
Record both the direction and approximate amount of the compass
deflection. NOTE: When reporting the compass deflection, describe its
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Part Two: The Source and Movement of Charge
action in terms of a clockwise or counterclockwise rotation. Using such
terminology will allow us to compare results with others with less
confusion. _________________________________________________
_________________________________________________________
_________________________________________________________
4.
Without moving the compass, disconnect and reconnect different
connecting wires to be sure that the effect is reproducible. Is the same
effect noted no matter which wire is disconnected and then
reconnected? Record your observations (amount of deflection, direction
for each wire).
_______________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
5.
Without moving the compass, move the circuit. Does the
magnitude/direction of deflection depend on which wire it is?_______.
6.
Without moving the compass, disconnect the battery and take one of the
batteries away. Reconnect the circuit and record your observations.
Does the magnitude or direction of deflection change? If so,
how?_____________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
________________________________________________________
7.
What effect, if any, do you think reversing the connections to the battery
pack would have on compass deflection and bulb brightness? Explain._________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
8.
Reverse the connections to the battery pack without moving the
compass or anything else in the circuit. You may find it easiest to
disconnect the wires from the battery pack, turn the battery pack around,
and reconnect the wires. Record your observations regarding amount,
direction of compass movement and bulb activity. Did they agree with
your predictions?
_________________________________________________________
_________________________________________________________
____________________________________________________
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Part Two: The Source and Movement of Charge
9.
Write a paragraph describing the relationship between the compass
deflection and the lighting of the bulbs. Also compare the activity in each
of the connecting wires as implied by the compass deflections.
________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________
Exploration 4: Capacitors
Equipment
2 capacitors (25,000 μF)
6-volt bulbs (blue base)
Connecting wires
Battery Pack
8 AA batteries
Stopwatch
multimeter
+
charging
discharging
Experiment 1: One capacitor and one bulb
Make sure capacitor is uncharged before starting the experiment by briefly
connecting the capacitor terminals with a wire (repeat at the start of each
experiment).
1. Connect the “charging” circuit shown above. Make sure the positive terminal
of the capacitor is connected to the positive end of the battery pack and same
for negative terminals. While still connected, measure and record the potential
difference across a) the battery pack terminals and b) the capacitor terminals.
Vbat_______________
Vc _______________
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Part Two: The Source and Movement of Charge
Record your observations of the light bulb below. Why did this happen?
Answer by comparing the potential difference of the capacitor with the potential
difference of the battery pack and how that influences the charge flow.
2. Remove the battery and reconnect one light bulb. Use the stopwatch to
measure how long it takes for the light to go out. Make a mental note regarding
the brightness of the bulb because you will be comparing the brightness to
other circuits.
_________s
3. Explain what happened as the bulb lit up and then went out, in terms of
charge and potential difference:
4. Calculate the amount of charge stored by the capacitor: _________C
Show your work.
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Part Two: The Source and Movement of Charge
5. Calculate the energy stored by the capacitor: ___________J
Show your work.
Experiment 2: Two capacitors in parallel and one bulb
1. Connect the capacitors in parallel (diagram shown below) and charge as
before. This procedure doubles the capacitance of the circuit. It is not
necessary to connect the bulb for the charging procedure.
2. Measure the voltage across the battery, and across each capacitor after
charging. How do they compare?
3. Remove the batteries and connect the light bulb. Measure the time it takes
for the light to go out
___________s
Compare the time and brightness with those from Experiment 1 (Repeat
Experiment 1 if you need to compare the brightness).
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Part Two: The Source and Movement of Charge
4. By what factor has the amount of charge stored on the 2-capacitor system
changed, compared with the charge stored in Experiment 1?
Q2/Q1 = _______________
5. By what factor has the amount of energy stored on the 2-capacitor system
changed, compared with the charge stored in Experiment 1(add the energies of
each capacitor)?
EPE2/EPE1 = _______________
Experiment 3: One capacitor and one bulb with half ΔV
1. Change the battery pack to ½ the original voltage by
a. Removing the battery opposite to the positive terminal.
b. Disconnecting the negative terminal and reconnecting the black lead to the
metal hole at the now empty space (ask if you need help).
Now charge the capacitor.
2. Remove the batteries and connect the light bulb. Measure the time it takes
for the light to go out.
___________s
Compare the time and brightness with those from Experiment. 1.
3. By what factor has the amount of charge stored on the lower voltage system
changed, compared with the charge stored in Experiment 1?
Q3/Q1 = _______________
4. By what factor has the amount of energy stored on the lower voltage system
changed, compared with the charge stored in Experiment 1?
EPE3/EPE1 = _______________
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Part Two: The Source and Movement of Charge
Experiment 4: Two capacitors in parallel, one bulb, half ΔV
1. Connect the 2nd capacitor in parallel with the first and charge as before.
2. Remove the batteries and connect the light bulb. Measure the time it
takes for the light to go out
___________s
Compare the time and brightness with those from Experiment 1:
3. By what factor has the amount of charge stored on this system changed,
compared with the charge stored in Experiment 1?
Q4/Q1 = _______________
4. By what factor has the amount of energy stored on this system changed,
compared with the charge stored in Experiment 1 (add the energies of each
capacitor)?
EPE4/EPE1 = _______________
5. Based on the results of this experiment, do you think the time it took for the
bulb to go out was a function of the charge stored, or the energy stored?
Explain your answer.
6. Based on the results of the this experiment, do you think the brightness of
the bulb was a function of the charge stored, or the energy stored? Explain
your answer.
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Part Two: The Source and Movement of Charge
Check your Understanding
1. For each of the situations illustrated below, draw either the schematic or the
pictorial representation of a circuit, depending on the representation shown.
1. Pictorial or real world representation
1. Schematic or physical representation
2. Pictorial or real world representation
2. Schematic or physical representation
+bat-
capacitor
3. Pictorial or real world representation
5. Schematic or physical representation
2. For each of the sets of connections shown on the next page:
a. Decide which bulb(s) in each figure will light. Record the bulb number
on the lines provided below the figures.
b. On each diagram, draw in the conducting path for moving charges for
each circuit. Your paths should include the battery and should indicate
which bulbs will be lit.
c. Draw the schematic or physical representation for each figure in the
space at the bottom of the page.
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Part Two: The Source and Movement of Charge
Indicate which bulb(s) will light, if any:
Figure 1 _______ Figure 2 _______ Figure 3 ________ Figure 4 ________
Make your circuit diagrams here. If the circuit is not complete, draw a space
between the bulbs. If the bulbs light, show connection between bulbs with a
connecting line.
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