Answer the following questions relating to the adjoining circuit diagram. When the voltmeter is connected across the 100W resistance the ammeter reading is 0.04 amp.
The resistance of the voltmeter is
Answer & explanation
Correct answer: option 4
$ I = \frac{3.4}{3+2+ 100R_v/100+R_v} = 0.04$
$ \frac{100R_v}{100+R_v} + 5 = 85$
$ \Rightarrow \frac{100R_v}{100+R_v} = 80$
$ \Rightarrow 5R_v = 400 + 4R_v $
$ R_v = 400\Omega$