Activity 8
Ohms Law and Circuits
Name:_____________________________
PHYS 010
Date:______________________________
Partners:__________________________
__________________________
__________________________
Purpose:
To study the relationship between voltage, current and resistance and apply this
understanding to simple series and parallel circuits.
Materials:
1. 2 identical bulbs, and bulb holders
2. 4 AA batteries. Quad battery holder and single battery holder.
3. Alligator clips (4 or more)
4. ammeter
5. Multimeter
6. A selection of resisters
Part 1 – Ohms Law.
The goal here is to demonstrate Ohms law: V = I  R
Use the multimeter, set for making resistance measurements, to measure the resistance of
each of your resistors, and enter the value in the table that follows.
Trial
Measured
Resistance
(Ω)
Measured
Current
(A)
Calculated
Voltage
(V)
Measured
Voltage
(V)
1
2
3
4
5
Using 4 AA batteries as the power source, build the following circuit. Do not make the
final connection until you are ready to make measurements, as having the circuit live will
drain down your batteries. Use the ammeter provided to make the current measurements,
and the multimeter to measure the voltage dropped across the resister.
Note the symbol:
Rev 09-01
refers to a resister
1/12
Activity 8
Ohms Law and Circuits
PHYS 010
V
A
6V
Questions & Activities:
1. Do your calculated voltages agree well with the measured voltage drop? If noyt,
do you have any explanation why not?
2. Plot your results on the following graph.
1.000
0.900
0.800
Current (A)
0.700
0.600
0.500
0.400
0.300
0.200
0.100
0.000
0
50
100
150
200
250
Resistance
Rev 09-01
2/12
Activity 8
Ohms Law and Circuits
PHYS 010
3. Mystery Resister. You are now given a mystery resister. Without measuring the
resistance with the multimeter, put it into your circuit, measure the current, and
using the graph predict what the resistance is.
4. Now determine the resistance using the colour code, as follows: What resistance
do you predict for the resister based on colour code?
5. Does your measured/calculated value agree with the colour code prediction?
Rev 09-01
3/12
Activity 8
Ohms Law and Circuits
PHYS 010
Part 2 – Series circuit with one bulb
Consider you have a battery, a bulb in a bulb holder, and a circuit as follows.
Caution: Don’t connect 2 AA batteries to the
circuit if you only have ONE bulb connected.
You’ll burn out the bulb!
Bulb
Battery
1. PREDICT: In the diagram above, if you measure current in different parts of the
circuit with an ammeter will you -get different or identical measurements?
2. OBSERVE: Have your group connect the circuit so the bulb lights. Use the
ammeter to measure the current in the following places: between the positive
terminal of the battery and the bulb (1), and then between the bulb and the
negative terminal of the battery (2). Note: the ammeter must be connected in
series to the circuit to work properly.
Measurement 1 (mA):
Measurement 2 (mA):
Rev 09-01
4/12
Activity 8
Ohms Law and Circuits
PHYS 010
Were your predictions about current measurement correct?
Part 3 – Series Circuit with two bulbs
1. PREDICT: You now have two identical bulbs and one battery. You still want
the electricity to flow in a continuous loop.
a. Sketch how you would build the circuit using two bulbs.
b. Predict if one bulb will be brighter than the other, and if so, which one.
c. Predict if the current in the circuit will change when you add a second
bulb compared to the circuit is Part 2. Explain your reasoning.
Rev 09-01
5/12
Activity 8
Ohms Law and Circuits
PHYS 010
2. OBSERVE: Now you can assemble the circuit.
a.
Is one bulb brighter than the other? Are the two bulbs each brighter,
dimmer, or the same brightness as when you only had one bulb in the
circuit? Explain.
b. Measure the current on either side of the battery like you did in the onebulb part of this ctivity, and list your results below.
Measurement 1 (mA):
Measurement 2 (mA):
Compare these results to the current measured with only 1 bulb in the
circuit. Do these results make sense? Explain.
3. PREDICT: What will happen to the bulb brightness and current in the circuit if
you add a second battery?
4. OBSERVE: Now connect the second battery so the positive terminal of the first
battery touches the negative terminal of the second battery. How did the
brightness of the bulbs change compared to when you were using just one
battery?
Rev 09-01
6/12
Activity 8
Ohms Law and Circuits
PHYS 010
5. Use the ammeter to measure current at three points in the circuit: between the
batteries and the first bulb (1) , between the bulbs (2) , and between the second
bulb and the batteries (3).
Measurement 1 (mA):
Measurement 2 (mA):
Measurement 3(mA):
Are your results from question 4 consistent with the current you measured here?
How does the current change when you add the 2nd battery? Does this make
sense?
6. PREDICT: What will happen if you unscrew one of the light bulbs? Will the
other two appear brighter? Will something else happen? Explain.
7. OBSERVE: Try it! With the circuit closed (i.e. with both lights shining)
carefully unscrew one of the light bulbs. Write down your observations here:
8. You will have noticed the conditions that lead to current increase and decrease in
your circuit as you change the number of batteries and the number of light bulbs.
From your observations, on what factors does the current in a system depend?
Rev 09-01
7/12
Activity 8
Ohms Law and Circuits
PHYS 010
9. If you saw that the current did not decrease by exactly a factor of two when you
added a second bulb, what other factors might have affected the results?
10. As the title of the lab indicates, this is what is called a series circuit, where the
electricity flows in a loop from one terminal of the battery, through the circuit, to
the other terminal. Strings of Christmas-tree lights used to be configured in a
series circuit similar to what you constructed, but with several dozen bulbs instead
of just three. Brainstorm some advantages and disadvantages of using a series
circuit for a string of lights:
Part 4 – Parallel Circuits
Diagram:
battery
Light bulbs in
holders
Procedure:
1. To determine the baseline current, connect a simple series circuit with ONE bulb,
and one battery. Measure the current with the ammeter (in series) of this basic
series circuit:
Rev 09-01
8/12
Activity 8
Ohms Law and Circuits
PHYS 010
2. PREDICT: If you add a 2nd bulb in parallel, as shown in the diagram above, will
both bulbs be equally bright, or will there be a difference in brightness? Explain.
What will happen to the brightness of the first bulb? Also, will the current in the
two branches differ, or be the same?
3. OBSERVE: Connect the second bulb to the circuit as shown in the diagram.
Record your observations about the brightness of the bulbs. Were your predictions
correct?
4.
(c)
(a)
1
2
(b)
This parallel circuit can be thought of as two current loops, as indicated in the
above diagram. Measure the current for the following components. Note: to
measure current properly, the ammeter must be connected in series.
Current in loop 2, between the two bulbs – noted by ammeter position (a):
Current in loop 1 – noted by ammeter position (b):
Total current in the circuit - noted by ammeter position (c):
Rev 09-01
9/12
Activity 8
Ohms Law and Circuits
PHYS 010
5. a) Compare the currents across loop with each other. What is the relationship
here?
b) Compare the currents in each loop with the total current in the circuit. What is
the relationship here?
c) Compare the total current in parallel with the total current for two bulbs in
series, with one battery. (May need to refer back to Series Circuit activity.)
Explain your findings.
Questions:
1. Remove one of the bulbs. What happens to the brightness of the other one?
Why?
2. Using the multimeter, measure the voltage across each bulb in the parallel circuit.
Bulb 1: (V)
Bulb 2: (V)
Rev 09-01
10/12
Activity 8
Ohms Law and Circuits
PHYS 010
Compare the voltages across each bulb, and compare these voltages with the
voltage of the battery:
Now, measure the voltage across one of the bulbs when the other one is
unscrewed from its holder:
Is the voltage across a bulb changed when an identical bulb is placed in parallel
with it? Explain how this is different from a series circuit.
3. Are the outlets in your home arranged in parallel or series? Why are they
designed this way?
4. If you were to design your own chandelier for your dining room, would you want
the bulbs to be in series, or parallel? Explain why.
Rev 09-01
11/12
Activity 8
Ohms Law and Circuits
PHYS 010
Summary and Suggestions for the Future:
a.
What were the important concepts of physics/science that you learned from this
activity? What else did you learn?
b.
Can you think of alternative hands-on ways in which these concepts could be
demonstrated?
c.
What changes (if any) would you make to teach these activities in a Grade 7-8
classroom
Rev 09-01
12/12