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 voltage read by the volt meter is
Answer & explanation
Correct answer: option 3
$ 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$
$ R_{eq} = \frac{100\times 400}{500} = 80\Omega$
$ \text{Voltmeter reading } = 80\times 0.04 = 3.2V$