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Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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Ohm’s Law and Equivalent Resistance
Electric current 𝐼 is a measure of the rate of flow of charge and is measured in
amperes (𝐴). In order to have a current, a potential difference or voltage, 𝑉 must
exist across the wire. It is measured in volts (V) and is the change in the electric
potential energy per unit charge. Therefore 1 volt is equivalent to 1 joule per
coulomb (1𝑉 = 1 𝐽/𝐶).
The relationship between current and voltage is defined by the object’s
resistance 𝑅 . It is a measure of the resistance to the motion of charged particles
and is measured in ohms (𝛺). The current that flows through an object is related
to the potential difference. This is the subject of Ohm’s law.
A resistor is any object that passes current (a conductor) and dissipates energy
in the form of heat.
Ohm’s law states that for a conductor with resistance 𝑅 carrying a current 𝐼 , the
potential difference across the resistor is
𝑉 = 𝐼𝑅.
There are two ways that resistors can be connected:
Resistors in Series - A number of resistors are in series when the current
through each resistor is the same. You can recognize resistors in series by the
fact that there is only one path for the current to follow and as a result the current
goes through one at a time (in series). (See diagram below.)
I
I
R1
R2
I
Resistors in Parallel - A number of resistors are in parallel if the voltage across
each resistor is the same. You can recognize two resistors in parallel by the
fact that there are multiple paths for the current to take. In the diagram below the
current 𝐼 splits into two different currents, passes through the two resistors
(larger current through smaller resistor) and then recombines to the original
current 𝐼 .
I
I1
R1
I2
R2
I
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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When multiple resistors are connected in a circuit it is useful to consider the
equivalent resistance, 𝑅𝑒𝑞 , which is the resistance of a single resistor that
could replace the multiple resistors and have the same effect on the circuit i.e.
draw the same current from the power supply.
The formula for the equivalent resistance is different for both types of
connections:

Series connection for resistors:
𝑅𝑒𝑞 = 𝑅1 + 𝑅2 + ⋯

Parallel connection for resistors:
1
1
1
=
+
+⋯
𝑅𝑒𝑞 𝑅1 𝑅2
In an electric circuit, ammeters are connected in series and measure current.
Voltmeters are connected in parallel and measure voltage.
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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Prelab Questions
These questions need to be
completed before entering the lab.
Please show all workings.
Marker’s
Initials
Prelab 1
How are current and voltage related for a resistor?
Prelab 2
How do we determine the equivalent resistance of resistors in series? How do we
determine the equivalent resistance of resistors in parallel?
Prelab 3
Circle the appropriate choices below to complete the following sentences:
An ammeter is connected in series/parallel and measures current/voltage.
A voltmeter is connected in series/parallel and measures current/voltage.
STAPLE YOUR PRE-LAB TO THIS PAGE
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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Laboratory Worksheet
Name and Student Number:
___________________________
Partner:
___________________________
Date:
___________________________
TABLE 1:
Current (enter unit)
Voltage (enter unit)
TABLE 2:
Slope (enter unit)
Value
Experimental Uncertainty
CHECKPOINT:
y-intercept (enter unit)
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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QUESTION 1:
QUESTION 2:
QUESTION 3:
QUESTION 4:
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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QUESTION 5:
TABLE 3:
value (enter unit)
𝜹𝑹 (enter unit)
value (enter unit)
𝜹𝑹 (enter unit)
𝑅1
𝑅2
TABLE 4:
𝑅𝑒𝑞 (𝑆𝑒𝑟𝑖𝑒𝑠)
𝑅𝑒𝑞 (𝑃𝑎𝑟𝑎𝑙𝑙𝑒𝑙)
QUESTION 6:
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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QUESTION 7:
QUESTION 8:
QUESTION 9:
Physics 1021 Laboratory #6 Ohm’s Law and Equivalent Resistance
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QUESTION 10:
QUESTION 11:
QUESTION 12:
QUESTION 13:
Staple graph(s) to this the
reverse side of this page.