Programmed Review for Electrical Engineering, Third Edition
This text contains an organized review of the basic electrical engineering fundamentals, with 111 problems, solutions and explanations for the core electrical engineering concepts.
TABLE OF CONTENTS Programmed Review for Electrical Engineering, Third Edition
Ammeters
The problem in this section illustrates the difference in ac and dc current measurement.
Problem 2-16: AC AND DC AMMETERS
Q:
In the circuit below an ac and a dc source are connected in series with a 100 ohm load. Ammeters A 1 and A 2 are also in series with the circuit to measure ac and dc current. A 1 is a true rms ammeter, and A 2 is a D'Arsonval-type ammeter.
Determine:
the reading of A 1;
the reading of A 2;
the power dissipated in the load.
Answers
Q:
Ac voltmeters and ammeters for power frequencies are designed to indicate effective value, even for nonsinusoidal waveforms. Instruments for higher frequencies also give the effective value for sine waves, but for other waveforms, the reading is not the effective reading. The composite current I has an ac component and a dc component. These two components are calculated as follows:
(answer)
Meter A 1 reads I RMS, which is equal to the square root of the sum of the squares of the current components:
(answer)
Meter A 2 reads I dc = 0.25 amp.
(answer)
Power dissipated in the load is:
(answer)
If your answers are correct, go to Problem 2-17.
If your answers are not correct, review p. 27.
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