Electrical Circuits 1
EENG 50 Laboratory
Laboratory Experiment # 5
Ohm’s Law and Nonlinear Resistance
INTRODUCTION/ THEORETICAL INFORMATION
Ohm's Law
For many conductors of electricity, the electric current which will flow through them is
directly proportional to the voltage applied to them. When a microscopic view of Ohm's
law is taken, it is found to depend upon the fact that the drift velocity of charges through
the material is proportional to the electric field in the conductor. The ratio of voltage to
current is called the resistance, and if the ratio is constant over a wide range of
voltages, the material is said to be an "ohmic" material.
Resistance
The electrical resistance of a circuit component or device is defined as the ratio of the
voltage applied to the electric current which flows through it:
𝑽𝑽
𝑹𝑹 =
𝑰𝑰
If the resistance is constant over a considerable range of voltage, then Ohm's law, I =
V/R, can be used to predict the behavior of the material. Although the definition above
involves DC current and voltage, the same definition holds for the AC application of
resistors.
Whether or not a material obeys Ohm's law, its resistance can be described in terms
of its bulk resistivity. The resistivity, and thus the resistance, is temperature dependent.
Over sizable ranges of temperature, this temperature dependence can be predicted
from a temperature coefficient of resistance.
OBJECTIVES
•
•
•
•
•
•
To measure voltage across a component using a voltmeter
To measure current through a component using an ammeter
To measure resistance of a component using an ohmmeter
To calculate Voltage, Current, and Resistance using Ohm’s Law
To realize that some resistances are unstable.
To incorporate scientific method
MATERIALS
•
•
•
•
•
•
Battery / power supply
Low voltage Incandescent lamp
Jumper wires / solid connecting wires
Assortment of 10 resistors (different values of resistance)
Breadboard
Multimeters (Analog/ digital)
PROCEDURE
A. Ohm’s Law
1.
Select a resistor from the assortment, and measure its resistance with
your multimeter set to the appropriate resistance range.
•
Be sure not to hold the resistor terminals when measuring resistance,
or else your hand-to-hand body resistance will influence the
measurement!
2.
Record this resistance value for future use.
3.
Build a one-battery, one-resistor circuit.
4.
Set your multimeter to the appropriate voltage range and measure voltage
across the resistor as it is being powered by the battery.
5.
Record this voltage value along with the resistance value previously
measured.
6.
Set your multimeter to the highest current range available.
7.
Break the circuit and connect the ammeter within that break, so it becomes
a part of the circuit, in series with the battery and resistor.
8.
Select the best current range: whichever one gives the strongest meter
indication without over-ranging the meter.
If your multimeter is auto-ranging, of course, you need not bother with
setting ranges.
•
9.
Record this current value along with the resistance and voltage values
previously recorded.
10. Taking the measured figures for voltage and resistance, use the Ohm's
Law equation to calculate circuit current.
11. Compare the calculated current with the measured circuit current.
12. Taking the measured figures for voltage and current, use the Ohm's Law
equation to calculate circuit resistance.
13. Compare this calculated resistance with the measured resistance.
14. Finally, taking the measured figures for resistance and current, use the
Ohm's Law equation to calculate circuit voltage.
15. Compare this calculated voltage with the measured voltage.
• There should be close agreement between all measured and all
calculated figures.
• Any differences in respective quantities of voltage, current, or
resistance are most likely due to meter inaccuracies.
• These differences should be rather small, no more than several
percent. Some meters, of course, are more accurate than others!
16.
Substitute 9 more different resistors in the circuit and for each resistor,
re-take the resistance, voltage, and current measurements.
17.
Re-calculate these figures and check for agreement with the
experimental data (measured quantities).
18.
Also note the simple mathematical relationship between changes in
resistor value and changes in circuit current.
• Voltage should remain approximately the same for any resistor size
inserted into the circuit, because it is the nature of a battery to maintain
voltage at a constant level.
B. Nonlinear Resistance
1. Measure the resistance of the lamp with your multimeter.
•
•
This resistance figure is due to the thin metal "filament" inside the
lamp.
It has substantially more resistance than a jumper wire, but less than
any of the resistors from the last experiment.
2. Record this resistance value for future use.
3. Build a one-battery, one-lamp circuit.
4. Set your multimeter to the appropriate voltage range and measure voltage
across the lamp as it is energized (lit).
5. Record this voltage value along with the resistance value previously
measured.
6. Set your multimeter to the highest current range available.
7. Break the circuit and connect the ammeter within that break, so it becomes
a part of the circuit, in series with the battery and lamp.
8. Select the best current range: whichever one gives the strongest meter
indication without over-ranging the meter.
•
If your multimeter is auto-ranging, of course, you need not bother with
setting ranges.
9. Record this current value along with the resistance and voltage values
previously recorded.
10. Taking the measured figures for voltage and resistance, use the Ohm's Law
equation to calculate circuit current.
11. Compare this calculated current with the measured current:
NOTE: What you should find is a marked difference between measured current and
calculated current: the calculated figure is much greater. Why is this?
Questions:
a.
This behavior is very different from that of the resistors in the last
experiment. Why?
b.
What factor(s) might influence the resistance of the lamp filament?
c.
How might those factors be different between conditions of lit and unlit,
or between resistance measurements taken with different types of
meters?
This problem is a good test case for the application of scientific method. Once
you've thought of a possible reason for the lamp's resistance changing between lit and
unlit conditions, try to duplicate that cause by some other means. For example, if you
think the lamp resistance might change as it is exposed to light (its own light, when lit),
and that this accounts for the difference between the measured and calculated circuit
currents, try exposing the lamp to an external source of light while measuring its
resistance. If you measure substantial resistance change as a result of light exposure,
then your hypothesis has some evidential support. If not, then your hypothesis has
been falsified, and another cause must be responsible for the change in circuit current.
Table A. Ohm’s Law
Measured
Measured
Measured
Voltage
Current
Resistance
across the through the
(Rm)
resistor (VR) resistor (IR)
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
Calculated
Current
(I = VR / Rm)
Calculated
Resistance
(R = VR / IR)
Table B. Non-Linear Resistance
Measured
Measured Voltage
Measured
Resistance of
across the Lamp Current through
Lamp
(VL)
the Lamp (IL)
(RL)
DC Lamp
COMPUTATIONS:
Calculated
Voltage
(V = IR / Rm)
Calculated
Current
(I = VL / RL)
ANSWERS ON QUESTIONS:
1.__________________________________________________________________
2.__________________________________________________________________
3.__________________________________________________________________
RESULTS AND DISCUSSION:
______________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________.
CONCLUSION:
______________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_______________________________________________ .
Electrical Circuits 1
EENG 50 Laboratory
Laboratory Report # 5
Ohm’s Law and Nonlinear Resistance
Table A. Ohm’s Law
Measured
Measured
Measured
Voltage
Current
Resistance
across the through the
(Rm)
resistor (VR) resistor (IR)
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
Calculated
Current
(I = VR / Rm)
Calculated
Resistance
(R = VR / IR)
Table B. Non-Linear Resistance
Measured
Measured Voltage
Measured
Resistance of
across the Lamp Current through
Lamp
(VL)
the Lamp (IL)
(RL)
DC Lamp
Calculated
Voltage
(V = IR / Rm)
Calculated
Current
(I = VL / RL)
COMPUTATIONS:
ANSWERS ON QUESTIONS:
1.__________________________________________________________________
2.__________________________________________________________________
3.__________________________________________________________________
RESULTS AND DISCUSSION:
______________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_________.
CONCLUSION:
______________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
_______________________________________________ .
EENG 50 – CIRCUITS 1
First Semester A.Y. 2021-2022
Name: ___________________________________
Student No.: _______________
Course / Yr. / Sec.: _________________________
Date: _____________________
RUBRICS for LABORATORY REPORT
Laboratory Title:
_______________________________________________________________________________
CRITERIA
Punctuality
(20 pts)
Presentation of
Data Obtain
(30pts)
Excellent
Good
Submits
the
Laboratory
Report exactly
on the right
time.
Submits
the
Laboratory
Report after the
whole
class
submits
their
report but within
the day of the
class.
(20)
(19-11)
The
data
obtained in the
experiment was
arranged on a
table but when
graph, it cannot
be
interpreted
close to the
topic.
The
data
obtained in the
experiment is
presented in a
way that it is
close to the
topic of the
experiment.
(30)
Interpretation of
the Results
The explanation
given
was
related to the
topic of the
experiment.
(30pts)
(30)
Presentation of
the Report
Laboratory
Format (20)
The
report
format has met
all
the
requirement.
(20)
Final Score:
(29-20)
Most
of
explanation
given
related to
topic
of
experiment.
the
was
the
the
Needs
Improvement
Submits
the
Laboratory
Report
after the day of the
class but not more
than 4 days.
Un- acceptable
Submits
the
Laboratory
Report a week
after the time of
the class and
onwards.
(10-6)
(5-0)
The data obtained in
the experiment was
arranged as a list
with
no
distinct
arrangement
and
when
graph,
it
cannot
be
interpreted close to
the topic.
The
data
obtained in the
experiment is no
way close to the
topic
of
the
experiment.
(19-11)
(10-0)
Some
of
the
explanation
given
was related to the
topic
of
the
experiment.
(29-20)
(19-11)
The report had
erasures but the
order was intact.
(19-11)
The report had plenty
of erasures, staple
wires
were
not
covered but the order
was intact. (10-6)
The explanation
given was not
related to the
topic
of
the
experiment.
(10-0)
The
report
format does not
meet all the
requirement. (50)
Score