Question

A voltmeter has a resistance of 20 kilo ohm. When it is connected in series with external resistance R with 220 supply, it reads 160v . What is the value of R

Answer 1

it will b 5000 ohms.

as the voltmeter is connected across the resistance so the resistance is paralal with volt meter. so the volatage across the voltmeter = the voltage across resistance= 200v

now the current passing through the system of voltmeter & resistance is 0.05 A

which implies the equivalent resistance of the system will b around 4000A

so the 4000A is the paralal combination of 20000 ohm volt meter & the resistance (R)

so

4000=(20000*R)/(20000+R)

(calculation)

R= 5000 ohms