In the circuit shown in figure, the voltage across 8 Ω resistor is 20 V. Calculate the supply voltage.

• A. 18 V
• B. 38 V
• C. 27 V
• D. 47 V

Answer: (B)

Equivalent resistance of the circuit,
Req = (12||18) + 8
Req = 7.2 + 8
Req = 15.2 ohm
Source current = current through 8 ohm resistor, I = Vr/R8
I = 20/8
I = 2.5 A
Supply votage V = I*Req
V = 2.5*15.2
V = 38 V