Halliday, Resnick & Walker — Circuits: Problem 22

22 A simple ohmmeter is made by connecting a 9.00 V flashlight battery in series with a resistance R and an ammeter that reads from 0 to 1.00 mA, as shown in Fig. 27-33. Resistance R is adjusted so that when the clip leads are shorted together, the meter deflects to its full-scale value of 1.00 mA. What external resistance across the leads results in a deflection of (a) 10.0%, (b) 50.0%, and (c) 90.0% of full scale? (d) If the ammeter has a resistance of 20.0 \(\Omega\) and the internal resistance of the battery is negligible, what is the value of R?