(a) Explain why a voltmeter never reads exactly the correct value when it is applied to an electrical circuit to measure the voltage between two points. (b) For the circuit shown in Fig. 3.9, show...

(a) Explain why a voltmeter never reads exactly the correct value when it is applied

to an electrical circuit to measure the voltage between two points.

(b) For the circuit shown in Fig. 3.9, show that the voltage Em measured across

points AB by the voltmeter is related to the true voltage Eo by the following

expression:

Em

Eo

¼ RmðR1 þ R2Þ

R1ðR2 þ RmÞ þ R2Rm

(c) If the parameters in Fig. 3.9 have the following values,

R1 ¼ 500U; R2 ¼ 500U; Rm ¼ 4750U, calculate the percentage error in the

voltage value measured across points AB by the voltmeter.