"Suggested Exercises" whateverness (Mod.2 Sect2 part 5)

002902 L3 01 (binary/octet-stream)

Digital Multimeter Basics

Caption: : wOw

002902 L3 11 (binary/octet-stream)

Multimeter Circuit Testing

In this figure, the voltage across the battery is measured with a multimeter to make sure that electrical power is present.

002902 L3 12 (binary/octet-stream)

In this figure, the multimeter is used to measure the voltage at the output terminal of the switch to make sure that the switch is functioning.

Multimeter Circuit Testing

002902 L3 13 (binary/octet-stream)

Multimeter Circuit Testing

Caption: : Figure A shows a voltage measurement being taken at the junction of R1, R2, and R3, and Figure B shows a voltage measurement being taken at the junction of R3 and R4.

The measured voltage at each of these test points should be lower than the total power supply voltage because of the voltage drop across each of the resistors. If your measurement at both of these points reads the full power supply voltage, then R4 is open.

002902 L3 14 (binary/octet-stream)

Caption: : AC voltage cycles between positive and negative values while DC voltage remains constant.

Alternating current doesn’t change direction instantaneously. It starts at zero, rises to some maximum value, then begins to decrease toward zero again. At the zero point, the current’s polarity reverses, and the cycle repeats in the opposite direction. If we were to draw a graph of the voltage on our household power lines, the graph would look like Figure A. A plot of DC voltage (such as that from a battery) would look like the graph shown in Figure B.

AC vs DC

002902 L3 16 (binary/octet-stream)

AC vs DC

Caption: : These graphs show the relationship between peak and effective values of AC voltage. Figure A shows a graph of an AC waveform, and Figure B shows a graph of a DC waveform.

Look at Figure A. The figure shows two waveform graphs. Figure A shows a graph of an AC waveform, and Figure B shows a graph of a DC waveform. As you would expect, the DC voltage remains at its peak value all the time (115 volts in this case). The AC voltage, on the other hand, varies constantly. If we’re measuring an AC voltage with a multimeter, at what point on the graph will our measured voltage occur? Well, it can be shown mathematically that the effective value of AC voltage is actually about 70 percent of its peak value. Thus, if an AC voltage with an effective value of 115 volts was applied to a heating element, the element would produce the same amount of heat as it would with a 115-volt DC voltage applied. The effective value of an AC voltage is also called the RMS or root mean square value. This term refers to the mathematical process that’s used to calculate the effective value.