Lab 1: Introduction to Electrical Measurements

NAME:

1 Introduction

Figure 1: MASTECH Multimeter.

This lab concentrates on setting up two circuits- one with aresistor and one with a light bulb. This lab you will need touse a multimeter and/or LoggerPro on your computer. Inthis lab, we will learn about resistance and voltage, whichare new concepts for this course.

A resistor is something that resists the charge from mov-ing through the circuit. This circuit element prevents thecharge from moving through the circuit. In the case of thelight bulb, you will need to use a resistor to limit the currentflowing to the light bulb so it does not burn out immediately.

The voltage is the potential difference between twopoints. You probably encounter voltage everyday since abattery is rated to produce it. (We will cover this more thisweek!) We will be measuring the voltage of a battery.

2 Procedure

2.1 Resistor-Only Circuit

You will measure the potential difference of the battery withthe yellow MASTECH Multimeter. The battery says it should have a voltage of +1.5 V, however this is just thenominal voltage. The voltage of the battery can differ from its nominal value due to age, or a small difference inmanufacturing.

The procedure for the MASTECH Multimeter is as follows:

1. Plug the black battery lead into the black COM port using a black banana wire.

2. Plug the red battery lead into the red V/Ω/Hz port.

3. Turn the knob to the V range (2 V) (use the V without the squiggle).

4. Turn the RED ON/OFF on, and measure the voltage.

5. Record the Voltage below.

VOLTAGE = V

6. Reverse the leads, and record the Voltage below:

VOLTAGE (reversed) = V

Now, we will measure the resistance of of the resistor. The symbol for Resistance is Ω, which is ”Ohms”. Wewill learn this more in depth in another week.

1. To measure the resistance value, use the same leads from the battery and keep the other leads plugged intothe multimeter.

2. Turn the dial on the multimeter to dial, this resistor’s value is ≈ 22 Ω.

3. Record the value of the resistor

Resistance = Ω

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Figure 2: Current Probe for LoggerPRO

Now, we will use Loggerpro to measure the current inthe circuit.

1. Use the ”Current” box and connect it to Channel 1 ofthe LabQuest Mini.

2. In LoggerPro, go to Experiment/Set Up Sen-sor/LabQuest Mini/, and make sure that the CurrentProbe is in the appropriate channel.

3. Click on the current probe, and make sure it’s cali-brated to zero.

4. Connect the negative channel in the current probe (-)to the (-) lead on the battery (negative is black!) withthe banana plugs.

5. Connect the positive current (+) to the resistor witha banana plug.

6. Finally connect the resistor to the (+) terminal of thebattery

7. Record the Measured Current:

Current (I) = Amps

In Physics, we have an equation called Ohm’s Law which is

V = IR (1)

where we can calculate how much current is in a system with a voltage and a resistor. Using Ohm’s Law andyour measured values of V and R, calculate I:

Current (I) [calculated] = Amps

What was the percent difference between measured and calculated:

% Difference = %

2.2 Light bulb Circuit

Now, we will modify the circuit we already built and add in a light bulb. Where the resistor is currently pluggedin, remove it and replace it with a light bulb. Measure the current of the light bulb circuit.

Current (I) Measured = Amps

Calculate the Resistance of the light bulb using Ohm’s Law and your measured values of Voltage and Current.(Please do not measure the resistance of the light bulb - it does not work!!!)

Resistance Calculated = Ohms

3 Calculation

Assume that your circuit’s current is 0.068 A, and you let your light bulb run for 30 seconds. How many electronspassed through the wire in that time?

4 Clean Up

Before leaving the laboratory, please dismantle any circuits or connections that you have made. Place the wiresin one pile and return the meters to their boxes. For the rest of the semester, please slide chairs back under thelab benches to facilitate duties of our technical staff.

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