Question

In the given circuit the voltmeter reads 30 volt. The resistance of the voltmeter is
1)750 ohm

2)200 ohm
3)100 ohm
4)3000 ohm​

Answer 1

Answer:

200 ohm because it's speed is less

Answer 2

Answer:

The value of the resistance of voltmeter will be equal to 3000Ω  .

Therefore the option (4) is correct.

Explanation:

Given in the figure that the two resistance 1000Ω series with 1500Ω  

Consider that  R is the resistance of the voltmeter.

When we consider both resistance:

$R_{net}=\frac{1500R}{1500+R}+1000$

$R_{net}=\frac{1500R+1000R+15*10^{5}}{1500+R}$

$R_{net}=\frac{2500R+15*10^{5}}{1500+R}$

Then $I_{net}=\frac{60(1500+R)}{2500R+15*10^{5} }$                               .................(1)

When we consider circuit only with 1500Ω :

$R_{net}=\frac{1500R}{1500+R}$

Then $I_{net}=30(\frac{1500+R}{1500R})$                                  .................(2)

Compare eq.(1) and (2):

$\frac{60(1500+R)}{2500R+15*10^{5} }=\frac{30(1500+R)}{1500R }$

$3000R=2500R+15*10^{5}\\3000R-2500R=15*10^{5}\\500R=15*10^{5}$

∴  $R=3000$Ω