Question

The voltage across 6Ω resistor is __________

(a) 7.5V

(b) 6.78V

(c) 20V

(d) 8.5V

I got this question in a national level competition.

This interesting question is from Thevenin and Norton Equivalents,  More on Deriving a Thevenin Equivalent topic in section Techniques of Circuit Analysis of Electric Circuits

Answer 1

Correct choice is (d) 8.5V

Best explanation: Remove the resistor across which voltage is to be calculated and short circuit it. By using short circuit current and resistance calculate the current across 6Ω resistor and thereby voltage. (In this 10Ω resistor is also short-circuited since 10//0).