EF 152 – Physics for Engineers
Task 1.
A meter is a measuring instrument. An ammeter measures current, a voltmeter measures the potential difference (voltage) between two points, and an ohmmeter measures resistance. A multimeter combines these functions, and possibly some additional ones as well, into a single instrument.
Ammeter : Measures the current
Spring, 2011
To measure current, the circuit must be broken to allow the ammeter to be connected in series.
That means you will need to replace the ammeter’s sensors with one of the wires. ( All the current flowing in the circuit must pass through the ammeter).
To accurately measure the current the Ammeter must have a _______ resistance.
Notice that the current has a direction . The measurement can be positive or negative.
Voltmeter : Measures the voltage
To measure potential difference (voltage), the circuit is not changed: the voltmeter is connected in parallel.
To accurately measure the current the Voltmeter must have a _______ resistance.
Notice that the voltage (potential difference) can be positive or negative.

EF 152 – Physics for Engineers Spring, 2011
Ohmmeter : Measures the resistance
An ohmmeter does not function with a circuit connected to a power supply. If you want to measure the resistance of a particular component, you must take it out of the circuit altogether and test it separately.
(To measure resistance, the component must be removed from the circuit altogether).
Ohmmeters work by passing a current through the component being tested
Task 2.
Measuring voltage :
The voltage between two points is a short name for the electrical force that would drive an electric current between those points .
The symbol for voltage (battery) is: and units are Volts (
).
Notice convention sign on the battery. We will focus on potential difference later this week.
Use your multimeter to measure the voltage on a D-cell battery. Use the different tolerances on your multimeter.
How does that change your measurement?
Measuring resistance :
The electrical resistance of an object is a measure of its opposition to the passage of an electric current.
The symbol for a resistor is: and units are Ohms (
).
Please take a look at the picture on the next page to see how resistors are color coded:

EF 152 – Physics for Engineers Spring, 2011
Choose three different resistors from your packet and calculate their resistance.
Check your calculations using the multimeter. Use the different tolerances on your multimeter. How does that change your measurement?
Calculated resistance ( Ω) Measured resistance ( Ω)
Resistor 1
Resistor 2
Resistor 3
Your multimeter can also be used to calculate the current in the circuit.
The electrical current is a flow of electric charge or the rate of flow of electric. This electric charge is typically carried by moving electrons in a conductor such as copper wires.
The SI unit for measuring the rate of flow of electric charge is the Ampere (A).
We will measure currents in on the next task.
Task 3.
Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.
V I R
V- voltage (potential difference) [v]
I- current [A]
R- resistance [Ω]
Go over the description of Experiment 1 a. Use your wires to make connections between the springs, one light bulb and one battery.
Measure the current on the light bulb when the light is on : ___________ [A]
Measure the current again, but now change the polarities of your multimeter sensors (‘switch them’).
What happened to your current?
Using ohm’s law, calculate the resistance of the light bulb ____________[
Ω]
Draw the circuit.

EF 152 – Physics for Engineers Spring, 2011
Circuit 1 b. Use your wires to make connections between the springs, two light bulbs and one battery. Make sure you connect your bulbs in series.
Measure the current on the 2 light bulbs when the light is on : ___________ [A]
Using ohm’s law, calculate the resistance of the2 light bulbs ____________[ Ω]
How do you compare it to the resistance of one light bulb (in the previous question)?
Draw the circuit
Circuit 2 c. Use your wires to make connections between the springs, two light bulbs and two batteries . Make sure you connect your bulbs in series.
Measure the current on the 2 light bulbs when the light is on : ___________ [A]
How do you compare the current to the previous one calculated in b. Explain why.
Using ohm’s law, calculate the resistance of the 2 light bulbs ____________[
Ω]
Draw the circuit
Circuit 3

EF 152 – Physics for Engineers Spring, 2011
The measurements will not be accurate enough. We are measuring very small numbers and the multimeter has a percentage reading error.
Use the resistance calculated in part a to calculate the current in part b and c.
The resistance calculated in part a is: ___________
When using one battery (1.5 v) and two bulbs (connected in series) the current will be:
When using two batteries (1.5 v each) and two bulbs (connected in series) the current will be: