Name:
Lab Partner(s):
Date lab performed:
Dr. Julie J. Nazareth
Physics 133L
Section:
Basic Circuits
Real circuit diagram: This diagram is made to look like reality (boxes, wires, light bulbs, etc).
These diagrams must be drawn as you perform the lab – not at home later. You don’t always
have to connect your wires exactly as shown in the lab manual, as long as you have set up the
circuit correctly (series or parallel, and with the correct meter in the correct place). Draw the
diagram as you have hooked up your circuit – not what the lab manual shows. Be sure to label
the power supply in your diagram with + and -, and “PS” or “power supply.” Meters should be
labeled either as “ammeter” or “voltmeter” as appropriate. In your diagram, wires should attach
to the boxes (power supply, ammeter, or voltmeter) in the approximately correct locations.
Schematic diagram: This diagram shows all the circuit elements using symbols. If needed, you
may draw this diagram at home, using your real circuit as a guide. For full credit, do all of the
following.
• Include all elements that are in you real circuit (power supply, wires, resistors, ammeter
or voltmeter).
• Put a “+” and “–“ at your power supply symbol to indicate positive and negative sides of
the circuit.
• Use arrows to indicate the flow direction of conventional current. If there is a junction,
mark the flow direction with arrows along the different pathways.
• Label the current with the symbol “I_”. If there is a junction, label the different
pathways “I1”, “I2”, etc as described in the lab manual procedure for the particular step.
You may use ‘IPS’ for current provided by the power supply.
• Use resistor symbols to indicate the light bulbs – Don’t use a light bulb symbol. Label
the resistors as “bulb 1” and “bulb 2”, or “R1” and “R2”, as appropriate based on the
procedure in the lab manual for that particular step. Please keep bulb 1 and bulb 2
consistent throughout the lab.
• Use a circle with an “A” inside to represent an ammeter. This should be in series with
the resistor (light bulb).
• Use a circle with a “V” inside to represent a voltmeter. This should be in parallel with
the circuit element or portion of the circuit it is measuring. A voltmeter measures the
change in voltage from one side of a circuit element or part of a circuit, to the other side.
- Follow the procedure outlined in the lab manual.
- Use the correct units in tables, calculations or sentences.
- Empty parentheses in row/column headers of tables are for units.
- Remember that banana ends on leads may be stacked to form a junction.
Part A: Series Circuit
A-1: Connect the series circuit.
Lab: Basic Circuits
Updated 09/29/15
Question 1) Explain why both bulbs go out when you unscrew only one of the bulbs in a series
circuit.
A-2: Connecting an ammeter
Make sure that you DO NOT change the voltage setting on the power supply throughout
this section. Simply unplug the banana plug from the positive terminal of the power supply
when rewiring your circuit. This cuts off the current in your circuit until you plug it back
in.
Connect the ammeter in series BEFORE the first bulb to measure the current going into the first
bulb, I1 (see Figure 5, real circuit drawing on left side). Record the current in Table 1 and draw a
schematic diagram of the circuit. Next, connect the ammeter BETWEEN the two bulbs to
measure the current going into the second bulb, I2 (See Figure 5, right side). Record the current
in Table 1 and draw a schematic diagram of the circuit.
Schematic diagram (meter before 1st bulb)
Schematic diagram (meter between bulbs)
A-3: Connecting a voltmeter
Make sure that you DO NOT change the voltage setting on the power supply throughout
this section. Simply unplug the banana plug from the positive terminal of the power supply.
Remove the ammeter from the circuit and revert back to the series circuit of Figure 3.
Connect the voltmeter in parallel with the first bulb, V1 (see Figure 7, center real circuit
diagram), and record the voltage in Table 1. Next, connect the voltmeter in parallel with the
second bulb, V2 (Fig. 7, left diagram) and record the voltage in Table 1. Finally, measure the
voltage across the combination of the two bulbs, V3, by connecting the VΩ connection from the
voltmeter to the positive (or high) side of the first light bulb in the series and the COM
connection from the voltmeter to the negative (or low) side of the second light bulb in the series
(see Figure 7, right side). Record the voltage in Table 1.
Table 1: Current and voltage measurements for a two bulb series circuit
Type
Meter Name/#
Bulb 1
Bulb 2
Current, I (
)
I1 =
I2 =
Voltage, V (
)
V1 =
V2 =
Lab: Basic Circuits
Updated 09/29/15
Combination
-------------------V3 =
Part B: Parallel Circuit
B-1: Connect the parallel circuit (schematic diagram shown in Figure 8). Figure 9 shows how
you can stack banana plugs to form a junction. Remember, just because a schematic diagram
shows a long wire before a junction, doesn’t mean that you have to wire it that way in real
life. You can plug the stacked banana plugs directly into the power supply and have a
junction only a plug length after the power supply.
Question 2) Explain why the other light bulb remains lit, when you unscrew one of the bulbs
from the socket in a parallel circuit.
For B-2 and B-3, DO NOT change the voltage setting on the power supply between the
various circuit configurations. Simply unplug the banana plug from the positive terminal
of the power supply to change your circuit.
B-2: Measurement of current
a) Measure the current flowing into the top bulb (only), I1. This means you need to connect the
ammeter in series between the power supply and bulb, but AFTER the junction. Figure 10
shows one way to construct this circuit. Alternatively, you can stack two banana plugs as shown
in Figure 9 and plug that directly into the power supply. Record the current in Table 2. Draw a
real circuit diagram of the circuit YOU CREATED AND USED IN THE LAB EXPERIMENT–
don’t just copy Figure 10. Use your real circuit diagram to draw a schematic diagram.
Ammeter reading of current through top bulb only
Real Circuit diagram
Schematic diagram
b) Without changing the voltage on the power supply, reconnect the ammeter so it reads
current through the bottom bulb (only), I2. Record the current in Table 2.
c) Without changing the voltage on the power supply, reconnect the ammeter so it reads
current leaving the power supply (i.e., BEFORE the junction), I3. Record the current in Table 3.
Lab: Basic Circuits
Updated 09/29/15
B-3: Measurement of voltage
Remove the ammeter from the circuit and revert back to the two bulb parallel circuit.
a) Measure the potential difference (voltage) across the top bulb only, V1. Remember, you can
stack two banana plugs and plug that directly into the power supply – you don’t need a long wire
between the junction and power supply. Record the voltage in Table 2. Draw a real circuit
diagram of the circuit YOU CREATED AND USED IN THE LAB EXPERIMENT. Use your
real circuit diagram to draw a schematic diagram.
Voltmeter reading of voltage across the top bulb only
Real Circuit diagram
Schematic diagram
b) Without changing the voltage on the power supply, reconnect the voltmeter so it reads the
voltage across the bottom bulb only, V2. Record the value in table 2.
c) Without changing the voltage on the power supply, reconnect the voltmeter so it reads the
voltage across the power supply output, V3. This is equivalent to the voltage across the
combination of both bulbs in the parallel circuit. Make sure the rest of the circuit is still attached
and the light bulbs are lit when you take your reading. Record the value in table 2. Turn the
voltage on the power supply to zero. Turn off power supply. Dismantle your circuit.
Table 2: Current and voltage measurements for a two bulb parallel circuit
Type
Meter Name/#
Bulb 1
Bulb 2
Current, I (
)
I1 =
I2 =
Voltage, V (
)
V1 =
V2 =
Power Supply
I3 =
V3 =
*** You may want to calculate the meter uncertainty for your measured current and
voltage values before filling out Table 3 below. Definitely do the calculations first if your
data doesn’t exactly support the relationships you expected. ***
Table 3: Current and Voltage Relationships for Series and Parallel Resistors (Bulbs)
Current
Voltage
Relationship between
Relationship between
I1 and I2
V1, V2 and V3
Series Circuit
Parallel Circuit
Lab: Basic Circuits
Relationship between
I1, I2 and I3
Updated 09/29/15
Relationship between
V1, V2 and V3
Calculations: Use Appendix Table C-2 to help you determine the uncertainty in the electronic
meter for the current and voltage measurements listed below. Show the calculations - that means
write out the math and the end result. Record your final answers as best estimate ±
uncertainty (ie., measured current or voltage ± meter uncertainty). Include units and round
properly for the final answer. (See Do’s and Don’ts #26 for help). Use the space provided, or
use an attached sheet of paper with the required calculations labeled so I can tell what is what.
Series circuit (Get data from Table 1)
Bulb 1 current (I1) uncertainty:
I1 =
±
Bulb 1 voltage (V1) uncertainty:
V1 =
±
Bulb 2 voltage (V2) uncertainty:
V2 =
±
Combination voltage (V3) uncertainty:
V3 =
±
Parallel Circuit (Get data from Table 2)
First bulb current (I1) uncertainty:
I1 =
±
Second bulb current (I2) uncertainty:
I2 =
±
Combination current (I3) uncertainty
I3 =
±
Power supply voltage (V3) uncertainty
V3 =
±
Lab: Basic Circuits
Updated 09/29/15
Questions: In complete sentences, answer the following questions in the space provided or on an
attached sheet of paper. (Hand-write on lined paper, green engineering paper, or type. It can
be the same paper as calculations.)
Question 3. (Instead of conclusion/summary paragraph): In one sentence, tell me what was the
goal of, reason for, or purpose of the Basic Circuits lab? (Write your answer as if you were
writing the introductory sentence to your summary/conclusion paragraph)
Question 4. In Table 3, you should have stated the relationship for the individual current values
(I1 and I2) of the two bulbs connected in series (section A-2 of experiment). How are these
current values (I1 and I2) related to the current leaving or entering the power supply? Explain
why.
Question 5. In section A-3 of the experiment, you were instructed to measure the voltage across
each bulb individually (steps one and two, V1 and V2 – left and center diagrams of Figure 7)
and across the combination of the two bulbs in series (third step, V3 – right hand schematic
diagram of Figure 7). If you had also measured the voltage across the power supply outlet
(making sure the rest of the series circuit is still attached and the light bulbs lit when taking
the reading), would you expect the measurement to match the voltage across bulb 1 (V1),
bulb 2 (V2), the combination of bulbs (V3), or none of these? Explain why this should be so.
There is no separate conclusion/summary paragraph for this lab experiment.
Lab: Basic Circuits
Updated 09/29/15