Download Ohm`s Law Lab

Ohm’s Law Lab
Name:
Date:
Period:
Ohm’s Law states that if the temperature of the resistance remains constant, the electric current (I)
flowing in a circuit is directly proportional to the applied voltage (V) and inversely proportional to the
resistance (R) of the circuit.
V
V
I
or R 
or V  IR
R
I
(a)
(b)
Above, Be sure to connect the voltmeter in parallel with the resistor and the ammeter in series with the
resistor. Note the positive (+) and negative (-) terminals of both meters in relation to the positive (+) and
negative (-) terminals of the voltage source. The circuit diagram for the apparatus is shown in (b).
Objective: During this investigation you will determine the values of resistors by applying Ohm’s Law.
Materials:
Voltage Source
6 “Banana” wires
4 different Resistors
Switch
1 Voltmeter
6 alligator clips
1 Ammeter
Warning! Do not twist resistor wires or do
any set-up other than what you are told to do
in this lab. If you damage any equipment you
will receive an automatic zero and will pay for
the equipment.
Procedure:
1. Connect the source of current, the switch (opened), an ammeter, and a low ohm resistor in series.
Place the voltmeter in parallel across the resistance.
2. Use the voltmeter to set the voltage source to 3 volts through the resistor. You will have to
change this each time.
3. NOTE Leave the switch open until your teacher has checked your circuit and told you to close
the switch. The meters you are using are expensive and can be ruined with improper use.
4. Close the switch and quickly read the meters. Open the switch as soon as you are done
recording the readings. Record your readings in the table on the back.
5. Disconnect everything in the circuit, use the voltmeter to set the voltage source to 6 volts and
repeat #2-4. You will have to change the meter sensitivity settings.
6. Repeat this procedure for three more different resistors until your table is completely filled in.
Data Table
V
Use R  for
I
calculations
Printed Value
R1
R2
R3
R4
Voltage (V)
Current (A)
Calculated
Resistance (Ω)
3V
6V
3V
6V
3V
6V
3V
6V
Conclusion Questions:
1. State the relationship between the current flowing through a circuit and the voltage and
resistance in the circuit.
2. Describe the proper placement of a voltmeter in a circuit.
3. Describe the placement of an ammeter.
4. Compare the printed values of the resistors you used with your calculated values. What could
affect your calculated value of the resistors?
5. Rank your resistors in order from the least to the greatest resistance. Rank the current you found
for each resistors at 3 V form the greatest to the least current. What do you notice about these
two lists?
6. A 60 W light bulb has a voltage of 120 V applied across it and a current of 0.5 A flows through
the bulb. What is the resistance of the light bulb?
7. A resistance of 60 Ω has 0.4 A of current flowing when it is connected across a battery. What is
the voltage of the battery?
8. The resistance of a small electric motor is 24 Ω. If the motor operates properly on a voltage of
6 V, what current does the motor require?