LAB:
Ohm’s Law
NAME: ____________________
DATE: ____________________
PERIOD: __________________
During this lab you will explore Ohm’s Law as well as the equation for electrical
power. Both of these equations are helpful in every day life from figuring what you can
and can’t plug into a wall socket to what you can and can’t do when wiring that new amp
into your car.
SAFETY NOTES:
During this lab, you will be using a low voltage power supply. On the front of the power
supply are two knobs colored red and black. These knobs are called binding post and
are where the electrical connections are made to the power supply. Do not make a
connection with a wire directly between the binding posts. This will cause a red light to
light for a short period then a fuse inside of the power supply will blow. The power
supply will be useless until the fuse is replaced. This means that instead of doing a lab,
you’ll get to do graded class work assignments. So, don’t mess up or allow others to
mess up!
The power supplies use 110 volts from the wall. To avoid possible electrocution
caused by spills, no drinks are allowed during this lab.
Finally this room is crowded so please be courteous when moving about.
I have been told of the safety concerns and the proper safety equipment to use.
___________________________________
initials
MATERIALS:
1.5 and 3 V power supply
0 -1 amp ammeter
Six jumpers
5 & 10 Ω resistors
0 - 5 volt voltmeter
GOALS:
ƒ Wire different elements of the lab in a mixture of series and parallel circuits.
ƒ Determine the current within three different circuits each at two different voltages and
compare them to the current predicted by Ohm’s law
ƒ Compute the electrical power in three different circuits, each at two different voltages.
ƒ Support TEKS 1A, 2B, 2C, 2D, 3A, and 6F.
PROCEDURE:
1. Set the voltage selector switch 1.5 volts and the power switch to off.
2. Build the circuit as shown using the 5 Ω resistor. The
is a jumper, the
is
an
ammeter,
the
is
a
voltmeter,
and
the
is
a resistor.
V
A
Power
Supply
+1
+
A
-
+5
V
A description of how to make this circuit follows:
a) Connect the power supply, ammeter and resistor in series. (Connect the +
(red) post of the power supply to the “1” post of the ammeter. Connect the –
(black) post of the ammeter to one side of the resistor. Connect the other side
of the resistor to the – (black) post of the power supply)
b) Connect the voltmeter in parallel with the resistor. (Connect the– (black) post
of the voltmeter to the side of the resistor connected to the – (black) post of the
power supply and the+ 5 (red) post of the voltmeter to the side of the resistor
connected to the ammeter)
3. Turn the power supply on.
4. Record the voltage and amperage in the data table.
5. Turn the voltage selector switch to three volts.
6. Record the voltage and amperage in the data table.
7. Repeat steps one through six using a 10 Ω resistor.
8. Connect the 5 Ω and 10 Ωresistors in series and repeat steps 1 through 6. A
sketch of this circuit is shown below.
Power
Supply
+1
+
A
-
V
+5
9. Using Ohm’s law, compute the current that should flow in the circuit by dividing
the voltage shown on the voltmeter by the resistance.
10. Using the voltage shown on the voltmeter and the current show on the ammeter
compute the electrical power used in the circuit.
CONCLUDE and APPLY:
1. Compare the actual current in the circuit to the current predicted by Ohm’s law, does
Ohm’s law work?
2. What happened to the power in each of the three circuits when you doubled the
voltage, did it double, more than double, or less than double?
3. Using a formula sheet, write down the formula for current, voltage, and resistance
which is known as Ohm’s law.
4. Using a formula sheet, write down the formula for electrical power.
5. Replace the “I” in the electrical power formula with voltage divided by resistance that
we get from Ohm’s law, and then simplify the equation. Does this explain what we
saw in question two?
DATA TABLE
Please read the procedures, especially steps nine and ten, for help and complete in this
table.
Voltage
supply
selector
switch
Voltmeter
reading
(V)
Resistance
(R)
1.5 V
5Ω
3.0 V
5Ω
1.5 V
10 Ω
3.0 V
10 Ω
1.5 V
15 Ω
3.0 V
15 Ω
Ammeter
reading
Computed
amperage
(V/R)
Power
(V X I)