Copy of Lab 2 - Ohm’s Law
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University of Massachusetts, Amherst *
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Course
152
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Electrical Engineering
Date
Jan 9, 2024
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Lab 2 - Ohm’s Law
Overview
In this lab you will learn about electrical resistance and its connection to
Ohm’s Law
. Ohm’s Law
simply states when a
voltage
is applied to a circuit, a
current
will flow through the circuit.
The amount of current is directly proportional to the applied voltage.
(1)
The portionally between the voltage and current is the
resistance
of the circuit. If the resistance
is a constant (it does not change if the applied voltage changes), then resistance obeys
Ohm’s Law:
(2)
The units of resistance are measured (not surprisingly) in ohms (
). In this lab you will use
resistors, circuit elements with constant resistance, to construct different circuits and test Ohm’s
law. Since a resistor’s resistance is constant, it is said to be
ohmic
. But not all circuit elements
are ohmic as you will see in later labs.
Part 1 - The Voltage Divider
A voltage divider is one the simplest circuit you can construct. I basically consist of two resistors
connected in
series
with each other. You will construct a voltage divider using the breadboard
and two 10,000
or 10k
. Remember 1k
= 1,000
.
From the Electricity and Magnetism Accessory Pack take out two 10k
resistors from the
pack.You can check if you have the right resistors using the color bands on them. The color
bands represent a numerical code for the resistance of the resistor. For at 4-band resistor the
color code is:
A helpful calculator for resistance from color code
The 10k
resistors in your E&M pack have the color bands brown (
1
), black (
0
), orange (
1000
),
and gold (
5%
). The color corresponds to either a digit, a multiplier, or a tolerance. So for the
case of a 10k
, the resistance is:
(
1
10 +
0
1)
1000
5%
= 10,000
5%
The tolerance means that the manufacturer rates the value of resistance within a percentage of
the nominal value. For example, the actual value of the resistance of the 10k
with a tolerance
of 5% may be between 9.5k
and 10.5k
.
Now construct a voltage divider. Here is a circuit diagram of what the voltage divider looks like:
You will also need to connect wires to the iOLab. The iOLab will function as both a voltage
source and a voltmeter and ammeter.
●
Connect the top end of the first resistor (R1) to the 3.3V voltage source on the iOLab.
●
Connect the bottom end of R1 to the A7 input. A7 will function as a voltmeter.
●
Connect the bottom end of the second resistor (R2) to the GND on the iOLab.
When you are done you voltage divider may look like this:
●
Red alligator clip is connected to 3.3V
●
Blue alligator clip is connected to A7.
●
White alligator clip is connected to GND.
Now let’s measure the voltage of the voltage divider. Setup the iOLab and iOLab app:
●
Connect the dongle to the USB port on your computer.
●
Turn on the iOLab.
●
Launch the iOLab app and select Analog 7 (A7) from the list of sensors.
●
Click Record and record the voltage measured by Analog 7. Allow the recording to run
for 5 to 10 seconds.
●
Click the Analog Mode button (bar chart button) on the toolbar in the app. Click and hold
the mouse arrow and drag the arrow across a segment of the data in the graph.
1.
Take a screenshot of the iOLab app with the data of the voltage divider and paste it here:
2.
Record the average voltage (
) +/- and the uncertainty (
) measured by A7 in the table
below:
Average Voltage (V)
1.6413 V +/- .0034 V
3.
How does the value of the average voltage compare to the voltage supplied by the
iOLab? Explain how the voltage divider “divides” the voltage in terms of the resistance of
the resistors. The voltage divider divides the voltage basically in half as the current has
to run through the resistors before reaching the output, resulting in the resistances
halving the input voltage by the time the current reaches the output. The resistors are in
series, thus the resistance is doubled and the voltage is halved.
Part 2 - Ohm’s Law
Now let’s test Ohm’s Law. You will construct a circuit and measure both the voltage across and
current through the circuit using the iOLab. First you will construct a circuit that looks like this:
●
Replace the second resistor R2 with a 1
resistor.
●
A 1
resistor has band colors brown(
1
), black(
0
), gold(
0.1
), and gold(
5%
).
Your circuit should look like this:
●
Red alligator clip is connected to DAC.
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1. Using the circuit shown below, set R1 and R2 as shown in the chart below. For each pair of
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R,
R,
E,
E,
R,
Figure a
Figure b
R,
E,
E,
R,
Figure c
them
Resistance Values, Voltage Drops, and Curfent Data Values
R,
(ohms) (ohms)
R2
V,
(volts)
4 1-716 V
1.47 V
V2
(volts)
0.268 V
V12
(volts)
| (amps)
26
1.984
1.978 V
65.6 MA
22
0.531 V
65.6 MA
18
1-978 V
12
0.920 V
L.182 V
0796 V
65.6 mA
1.980 V
1.981 V
14
16
1.062 V
65.6 mA
10
20
0.657V
1.325 V
24
1.985 V
65.7 mA
0- 398 V 1. 587 V
65.6 mA
please help
mewith Question
2 and 3
no calculation
needed just a faugafh combination from the voltage and current numbers for that combination. Can this be developed
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b. The currents passing through R1 and R3
C. The voltage across R1.
d. The voltage of the battery EMF.
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f.
R1
R3
S10
R1
U1
1.500
EMF
EMF
R5
100
V1
R2
$10
EMF
R4
EMF
EMF
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www
Units
Units
Units
Units
=1&₂
<
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Recommended textbooks for you
- Delmar's Standard Textbook Of ElectricityElectrical EngineeringISBN:9781337900348Author:Stephen L. HermanPublisher:Cengage Learning
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