Question

In the circuit, the voltmeter reads $30V$. What is the resistance of the voltmeter?

• A. $1200\Omega$
• B. $700\Omega$
• C. $400\Omega$
• D. $300\Omega$

Answer 1

The correct option is A $1200\Omega$

Now we know the formula

$V_a-30-300I+60=V_a$

$I=\frac{(60-30)}{300}$

$I=\frac{30}{300}$

$I=0.025A$

Also for the $I₁$

$I_1=\frac{V}{R}$

$I_1=\frac{30}{400}$

$I₁=0.075A$

Now $I=I_1+I_2$

$0.025=0.075+I_2$

$I₂=0.050$

Therefore for the resistance across voltmeter

$V=I_2\times R$

$R=\frac{30}{0.025}$

$R=1200\Omega$

Hence the resistance at the voltmeter is $1200$