Introductory to Circuits Activity
Advanced Physics / Physics
In this activity, you will explore how to set up several basic circuits
Part 1: Setting up a basic circuit
Items Needed for this part:
Ammeter to measure charge flow (current)
Christmas light bulbs
Switch
Compass
Voltmeter to measure voltage (energy per charge)
Connecting Wire (alligator clips and wire)
‘D’ batteries and battery holders
Part 1. A Basic Light Bulb circuit using the ammeter and voltmeter
You will need the following supplies for this circuit: voltmeter, ammeter, one light bulb, switch,
connecting wire, battery holder and three D batteries, and a compass.
There are two pictures of the circuit: one pic is the schematic (left); the pic is the right shows the circuit
with the devices. For your ammeter and voltmeter (red is positive; black is negative)
1. The battery holders are designed to hold from one up to four D batteries. Each battery has a negative
terminal and a positive terminal.
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2. Grab an ammeter. An ammeter is designed to measure current. The unit of current is the Ampere
(amp). Some ammeters, though, will measure currents in milliamps (mA). Ammeters will have hot (red)
terminals and a black (negative, ground) terminal. The ammeters we use typically have two or three hot
terminals. Always use the largest value of the hot terminal.
So, run a wire from the positive end of the battery holder to the red connector (+5A) of the ammeter.
Then run another wire from the black terminal along your table. This is what we mean when we say that
the ammeter is in series inside the circuit. It is part of the loop. Make sure the wire goes on top of your
compass so the wire is aligned with the compass needle (see pic). You might find it helpful to tape down
your wire with a bit of masking tape.
3. Now you are ready to hook up your one Christmas light bulb with the wire coming from neg end of the
ammeter (the one going over the compass). Light bulbs are non-polar (unlike the ammeter). This means
that you can hook it up either way and it will light. Attach another wire from the other end of your light
bulb to the switch. Keep your switch open for now. Finally attach another wire from the other end of
your switch to your neg battery terminal of the battery holder.
4. We are now ready to attach your voltmeter. A voltmeter measures the push of
the current in the circuit. Again, you will find that a voltmeter has a red (hot)
terminal (or more than one red terminal) and a black (ground) terminal.
So, you will want a wire coming out of the red (positive) terminal of the voltmeter
to the end of the Christmas light with the wire over the compass. Another wire will
go from the negative (black) terminal of the voltmeter to the other end of the light
bulb. Voltmeters are hooked up ‘across’ light bulbs.
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5. Now you can activate the switch and you should see action in your ammeter, voltmeter, compass, and
light bulb. Use the switch to activate and deactivate your circuit. The most common way is to activate
your circuit, take your readings and observations, and then deactivate your circuit to save battery life. (i.e.
don’t keep the circuit on if you are not taking readings.)
Observations:
What happens to the compass needle when you close your switch? You may need to open and close the
switch several times.
What is your reading on your ammeter?
What is your reading on your voltmeter?
How bright is your light bulb? (keep this brightness level in your head as we will make comparisons)
What did the compass do?
Can you explain why the compass did what it did?
Part 2: Adding more batteries with one light bulb:
Do not break down your circuit; keep the same circuit but change the number of batteries in your battery
holder and moving the battery holder wire.
Write down your ammeter, voltmeter, amount of compass deflection, and the level of bulb
brightness as you create your circuits. You can write these values down below the circuit.
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Observations about adding more batteries to a circuit:
1. What happens to the compass needle deflection as you go from one battery to four batteries?
2. What happens to the ammeter readings as you go from one battery to four batteries?
3. What happens to the voltmeter readings as you go from one battery to four batteries?
4. What happens to the brightness of the light bulb as you go from one battery to four batteries?
(My comments: Adding more batteries to a circuit increases how much energy goes to the light bulb. Your
compass needle should deflect more as you have more current, your ammeter readings should go up as you
have more current, your voltmeter readings should increase as you have more push from more batteries, and
the brightness should increase as your light bulb is given more electrical energy)
Part 3: Same number of batteries (three) but different number of light bulbs (series)
Keep three batteries in your holder and get the Christmas lights (2, 3, and 4 bulbs in series)
Write down your ammeter, voltmeter, amount of compass deflection, and level of bulb brightness as
you create your circuits. Just write your values above the circuit on this page.
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Observations about series circuits:
1. What happens to the compass needle deflection as you go from one bulb to four bulbs?
2. What happens to the ammeter readings as you go from one bulb to four bulbs?
3. What happens to the voltmeter readings as you go from one bulb to four bulbs?
4. What happens to the brightness of the light bulb as you go from one bulb to four bulbs?
(My comments: In this case, we keep the batteries the same and just change how many light bulbs we have in series. As we
increase the light bulbs, you should see less compass deflection as there is less current going through the circuit, you should
see lesser ammeter readings as there is less current, your voltmeter should also decrease as the voltage has to be spread
around to more light bulbs. Finally the bulbs should get dimmer as each light bulb gets less energy.)
Part 4: Same number of batteries (two) but different number of light bulbs (parallel). See the
directions on the next page on how to build the first circuit.
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1. First build circuit one with two batteries and determine the ammeter reading, voltmeter reading, the
degree of compass deflection, and level of bulb brightness. Write these values by the circuit drawing on
the previous page.
2. Now, let’s think about circuit #2. Creating
parallel circuits are much more confusing than series
circuits. One way to do this is to create nodes in your
circuit. A node is a
conductor to which you
can attach wires. If you
look at the drawing, the
nodes are what I have
circled. Notice that you
have a node on the left of
the circuit and one on the
right.
You will have your two
batteries and battery
holder, your ammeter, and
your compass. Setting up
these will not change from
circuit one.
However, we are going to
use metal paper clips as
your nodes. We can attach
our wires to these paper clips.
Examine the picture on your right above. Each line represents a wire. Take the wire from the negative
terminal of your ammeter (the one going above the compass) and attach it to your left side paper clip.
Attach wires from the light bulbs to the left and right side paper clips. Attach your voltmeter wires to the
paper clips. Finally take a wire from the right side paper clip to the switch. When you have all of your
connections, activate your switch and write down your ammeter, voltmeter, level of bulb brightness,
and amount of compass deflection on the previous page.
3. When you get circuit #2 done, try circuit #3. Keep all of your
circuit the same, just insert another light bulb onto the nodes. Write
down your ammeter, voltmeter, level of bulb brightness, and
amount of compass deflection on the previous page.
4. Try circuit #4 and add another light bulb onto the nodes. You
now have 4 light bulbs in parallel. Write down your ammeter,
voltmeter, level of bulb brightness, and amount of compass
deflection on the previous page.
Use your readings and observations to answer the questions on the
next page.
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Observations about parallel circuits:
1. What happens to the compass needle deflection as you go from one bulb to four bulbs?
2. What happens to the ammeter readings as you go from one bulb to four bulbs?
3. What happens to the voltmeter readings as you go from one bulb to four bulbs?
4. What happens to the brightness of the light bulb as you go from one bulb to four bulbs?
(My comments: Parallel circuits are interesting and much different than series circuits. As we add more light bulbs in parallel,
our compass deflection and ammeter readings should increase. This is because more current is generated by a decrease of
overall resistance decreasing. This is opposite of what we saw with our series circuit. Our voltmeter shouldn’t change.
Finally, the bulbs should stay about the same brightness, although this might be hard to discern.
Parallel circuits are much different than series circuits and we will get into this again later.)
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