OHM’S LAW
OBJECTIVE
The purpose of this experiment is to verify the linear relationship between current and voltage across resistors
in series and parallel connections.
APPARATUS
DC Voltage Supply
Digital Multimeter
Electric wires
Set of resistors
EXPERIMENTAL PROCEDURE
I
RESISTORS IN SERIES
a)
b)
c)
d)
Connect the two resistors in SERIES with the voltage source. Start incrementing the voltage by 2 volts
until you reach 12 volts.
For each voltage, measure the current in the circuit with the ammeter.
Graph the voltage versus current.
From the slope, calculate the total resistance of the circuit.
Find the percent error in the measurements of the total resistance.
Voltage
2
4
6
8
10
12
True
Calculated
Resistance Resistance
Error
Current
Resistance
II RESISTORS IN PARALLEL
a)
b)
c)
d)
Connect the two resistors in PARALLEL with the voltage source. Start incrementing the voltage
by 2 volts until you reach 12 volts.
For each voltage, measure the current in the circuit with the ammeter.
Graph the voltage versus current.
From the slope, calculate the total resistance of the circuit.
Find the percent error in the measurements of the total resistance.
Voltage
2
4
6
8
10
Current
Resistance
1
12
True
Calculated
Resistance Resistance
Error
QUESTIONS
1) Convert the unit of OHM into its combination of the fundamental SI units.
2) Two resistors of 20 Ω and 40 Ω are connected in parallel. What resistance must be connected in parallel
with them to make the total resistance equal to 12 Ω ?
3) A lamp is connected to a 90-V line. The current in the filament starts at 10 A and drops quickly
to 2 A . Why does this happen? By what factor does the resistance increase?
4) A 4.0-Ω resistor, an 8.0-Ω resistor, and a 12-Ω resistor are connected in series with a 24-V battery.
a) What is the current in each resistor?
b) Repeat for the case in which all three resistors are connected in parallel across the battery.
2