Question

In the circuit shown here, the ammeter $A$ reads $5$A and the voltmeter $V$ reads $20$V.Find the correct value of resistance

Answer 1

Voltmeters generally have a very high resistance and $\therefore$ a very small amount $(>0A)$ of current passes through them.

Thus,the amount of current flowing as $I_1,$(current through $R$) and $I_2$(current through $V$) will be $I=5$A

$\Rightarrow I_1+I_2=5$

$\therefore I_1=5-I_2$

As $I_2>0$

$\Rightarrow I_1<5$

Applying Ohm's law on the LHS of the above inequality,

$\frac{20}{R}<5$ since $I_1=\frac{20}{R}$

$\Rightarrow \frac{20}{5}<R$

$\therefore R>4\Omega$

$\therefore$ the correct value of resistance $R$ is slightly greater than $4\Omega$