Question

In the given circuit the current flowing through the resistance 20 ohms is 0.3 ampere while the ammeter reads 0.8 ampere. What is the value of $R_1$ in ohms?

Answer 1

Total current in ammeter is 0.8 A

Current through 20 ohm resistor is 0.3 A, hence the voltage across it is

$V=0.3\times 20=6V$

Current through 15 ohm resistor is

$I=\frac{V}{R}=\frac{6}{15}=0.4A$

Hence current through R1 is, I' = 0.8 - (0.3+0.4) = 0.1 A

Therefore,

$R1=\frac{V}{I^{\prime }}=\frac{6}{0.1}=60\Omega$