INTRODUCTION

We have learned about two units of measurement for electrical circuits: voltage (in volts) and current (in amps). Now we're going to learn about the third measurement: resistance.

Resistance:

The opposition to electron flow

There is another type of measurement, one that is similar to resistance. It is called continuity. We will learn about continuity in this lab, then you will take measurements for both resistance and continuity.

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OBJECTIVES

Learn about resistance and how to measure it using a multimeter
Learn about continuity and how to measure it using a multimeter

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WHAT IS RESISTANCE?

Previously we learned about voltage and current. Current is the flow of electrons. Voltage or electrical pressure is what pushes the current. Now we will be discussing resistance. Resistance is the opposition to flow. An example of resistance is friction. Friction opposes our feet from just slipping on the ground. Electrical resistance opposes the flow of current. More resistance means that it is harder to push the electricity and less resistance means it is easier to push the electricity. Everything has resistance as electricity tries to push electrons through it. Resistance is measured in a unit called ohms which is shown by the symbol Ω. One term that you will hear in industry is a load. An example of a load would be a motor, a light bulb, a solenoid, or a vacuum. These are all loads in the electrical system. They all have resistance. When voltage pushes current through a load, it allows us to do "work". Work can manifest itself in several different ways for example we can turn a motor, generate light, create a magnetic field, and heat an element. So, to help us understand how voltage works, it is important to first understand resistance.

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RESISTANCE

Watch the following videos to learn more about resistance.

https://www.youtube.com/watch?v=FFHUoWFtab0

https://www.youtube.com/watch?v=-PJcj1TCf_g

It needs to be understood that Resistance alone doesn't create heat or do work. Nor does voltage or current alone create heat or do work. The heat or work in a circuit comes from all three. The heat in a circuit comes when voltage pushes current through resistance. If the resistance is increased in the system and the voltage stays the same, then it is more difficult for the voltage to push the current. Hence, less current flow which means less heat or work. However, if the resistance stays the same and the voltage increases, then there is more current flow which increases the heat. So, a 100-watt light bulb is more work than a 60-watt light bulb. This means that the 100-watt light bulb gets more current. This is the same for motors. A large horsepower motor takes more current than a smaller horsepower motor. High voltage allows more work to be done because it pushes more current through the system. So, when more work is needed, the voltage is increased. This is why large factory motors run off 480V rather than the 120V that we see in our houses. This is also why the clothes dryer, which has a large motor in it and a lot of heat required to dry the clothes, uses 240V rather than the standard 120V. Because there is more work needed done.

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CIRCUITS

There is another measurement called continuity. In order to understand continuity, we need to learn a bit more about circuits. Watch the following video to learn about circuits. While watching, consider the following questions:

	Consider
	What is a circuit? What is required for electricity to flow through a circuit? What is the purpose of an insulator?

https://www.youtube.com/watch?v=VnnpLaKsqGU

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HOW TO MEASURE CONTINUITY AND RESISTANCE

Watch these videos to learn how to measure continuity and resistance.

How to Measure Continuity

How to Measure Resistance

The power must always be off when checking resistance or continuity. The power should be on when checking voltage but never for resistance or continuity.

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MATERIALS + TROUBLESHOOTING REFERENCE PAGES

Materials Needed for this Lab

Multimeter
Basic Electrical Trainer

Troubleshooting Reference Pages

Lockout Tagout
2-Way Switch
Light Bulb
Single-pole Breaker
Wire
Wire Colors
Circuit Breaker Box
Light Socket

Note: Keep this circuit wired up for the rest of module 1.

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TROUBLESHOOTING VIDEOS

No new components during this lab. Use the links above for reference.

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LAB INSTRUCTIONS

Watch the example lab video, and then perform the lab.

Use the Simple AC Light Circuit from Lab 1-2.

Note

Power must be off when checking resistance or continuity.
Using the continuity setting on the multimeter, show that a wire on the AC Light Circuit has continuity. This can be any wire of your choosing. Make sure to disconnect one side.

Note

For the next two steps, this is less than 200 Ω. So, it will be the same setting as the continuity setting on the meter.
Using the Ω setting on the multimeter, measure the resistance across a single wire of the AC Light Circuit. This can be any wire of your choosing. Make sure to disconnect one side.
Using the Ω setting on the multimeter, measure the resistance across the light socket and bulb of the AC Light Circuit. Make sure to disconnect one side of the light bulb.

	Remember!
	The screws will not give a reading unless they are tightened, or you can put the probes under the screws.

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SUBMISSION

Answer the questions in the quiz.