PHY 108: ELECTRICITY & MAGNETISM
EXPERIMENT 1 : OHM’S LAW
1. Objectives:
1) To confirm Ohm’s law by studying the relationship of voltage, current and resistance.
2) To make voltage and current measurements using a DMM in a resistive circuit to verify Ohm’s law.
2. Backgrounds:
Ohm’s Law: Ohm’s law states that electrical current in a resistive circuit is directly proportional to the
applied voltage and inversely proportional to its resistance.
𝐼=
Where
𝐸
𝑅
in amperes (A)
E is the applied voltage in volts (V).
R is the resistance in ohms ().
I is the current in amperes (A).
The larger the applied voltage is, the larger the current becomes. The larger the resistance is, the
smaller the current becomes.
Graphical Representation of Ohm’s Law: Ohm’s law can be represented as a straight line in x-y
coordinates as the current and the voltage have a linear relationship.
𝐼=
Where,
1
𝑅
𝐸
𝑅
1
= ∙𝐸
𝑅
represents the slope of the line with I on the vertical axis and E on the horizontal axis.
3. Procedures and Observations:
1. Pick 2.2 k, 4.7 k, and 10 k, from your laboratory kit as R1, R2, and R3.
2. Enter the colour codes and the nominal values of the resistors in Table 3-1.
3. Measure each resistance using the DMM and record the measured values in Table 3-1.
4. Connect the circuit shown in Figure 3-1 using R1 to start. Set DMM to measure voltage and
current simultaneously or separately.
Figure 3-1
5. Before turning on the DC power supply, have your circuit checked by the instructor.
6. With the voltage control knob set to the minimum (fully CCW), turn the DC power supply on
and set the voltage control to each voltage value shown in Table 3-1, beginning with 1 V.
7. For each voltage setting, measure and record the actual voltage and current values in Table 3-1.
8. Turn the power supply off.
PHY 108: Lab. 1
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PHY 108: ELECTRICITY & MAGNETISM
EXPERIMENT 1 : OHM’S LAW
9. Calculate the theoretical current values using the actual measured resistance values and the measured
voltage values. “Icalculated” can be obtained by dividing EMeasured by “Measured R.” These calculated currents
should be very close to the measured current, IMeasured. Enter the calculated current values in Table 3-1
under the heading “Icalculated”.
10. Compare the calculated currents with the measured, and if satisfied, proceed to the next step.
11. Repeat the above procedures from step 4 through 9, using the other two resistors.
R1
R2
R3
Nominal R: 2.2 k
Nominal R: 4.7 k
Nominal R: 10 k
Measured R:
Measured R:
Measured R:
Measured Values
EMeasured
IMeasured
ICalculated
Measured Values
EMeasured
IMeasured
ICalculated
Measured Values
EMeasured
IMeasured
ICalculated
1V
2V
5V
10 V
15 V
20 V
25V
Table 3-1: Voltage and Current Measurement and Calculation
PHY 108: Lab. 1
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PHY 108: ELECTRICITY & MAGNETISM
EXPERIMENT 1 : OHM’S LAW
Lab Report:
Date:
Name of the Students and IDs
(1)
(2)
(3)
#1: Record the data from Table 3-1.
R1
R2
R3
Nominal R: 2.2 k
Nominal R: 4.7 k
Nominal R: 10 k
Measured R:
Measured R:
Measured R:
Measured Values
EMeasured
IMeasured
ICalculated
Measured Values
EMeasured
IMeasured
ICalculated
Measured Values
EMeasured
IMeasured
ICalculated
1V
2V
5V
10 V
15 V
20 V
25V
#2: Comment on the measured current compared to calculated currents.
PHY 108: Lab. 1
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PHY 108: ELECTRICITY & MAGNETISM
EXPERIMENT 1 : OHM’S LAW
#3: Use the data obtained in Table 3.1 to plot Imeasured vs. Emeasured graph.
I vs. E
13
12
11
10
9
I (mA)
8
7
6
5
4
3
2
1
0
0
5
10
15
E (V)
20
25
30
#4: What does the inverse of the slope of your graphs represent? Illustrate using an example.
#5: Using your graph, estimate the current that would flow through each resister at E = 12 volts and
compare it with the calculated value (12 V/ RMeasured). Calculate the error.
For E = 12 V
Measured Resistance
Estimated Current
from Graph
Calculated Current
(12 V/ RMeasured)
% of Error
R1 =
R2 =
R3 =
PHY 108: Lab. 1
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