Question

A voltmeter of resistance 400 $\Omega$ is used to measure the potential difference across the 100 $\Omega$ resistor in the circuit shown in figure (32-E24). (a) What will be the reading of the voltmeter? (b) What was the potential difference across 100 $Omega$ before the voltmeter was connected ?

Answer 1

(a) $R_{eff}=\frac{100\times 400}{500}+200=280$

$i=\frac{84}{280}=0.3$

$100i=(0.3-i)400$

$\Rightarrow i=1.2-4i$

$\Rightarrow 5i=1.2\Rightarrow i=0.24$

Voltage measured by the voltameter $=100\times 0.24=24V$

(b) If voltameter is not connected $R_{eff}=(200+100)$

=$300\Omega$

i = $\frac{84}{300}=0.28A$

Voltage across $100\Omega =(0.28\times 100)=28V$