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Unit 4. Electric Circuits

In the previous unit we looked at voltage, current, and resistance individually. Now it’s time to put them all together and look at the concept of an electric circuit. As we’ll see, most circuits contain a voltage source, resistance, one or more switches, and some wire. We’ll get an introduction to two common circuit types, which are called series circuits and parallel circuits. We’ll also look at how to measure voltage, current, and resistance in circuits. Then we’ll consider some important safety precautions that you should observe whenever you work on circuits. Finally, we’ll start to use a powerful computer program called Multisim, which lets you build virtual circuits on the computer and make virtual measurements on them.

Unit 3 Review

Electric Circuits  
A Simple Circuit
More Schematic Symbols
Schematic Diagram for Flashlight
Closed Circuit and Open Circuit  
Testing a Switch

Polarity of Voltage Source  
Conventional Current Flow 

Protective Devices  

Wire Resistance  


Series versus Parallel
Components in Series
Series Circuit

Components in Parallel
Parallel Circuit

Measuring Voltage
Measuring Current
Measuring Resistance
A Common Mistake
Digital Multimeter
Multimeter Challenge Game

Electrical Safety
Electrical Accidents in the News

Unit 4 Review

Congratulations! You’ve completed the e-Lesson for this unit.