Question

Three resistors ($2,5$ and $7$ ohm) are wires as shown in the diagram. The equivalent resistance of this combination (in ohm) is:

• A. $\frac{59}{70}$
• B. $\frac{70}{59}$
• C. $\frac{1}{14}$
• D. $14$
• E. Cannot be determined without additional information.

Answer 1

The correct option is B $\frac{70}{59}$

Given : $R_1=2\Omega$ $R_2=5\Omega$ $R_3=7\Omega$

Equivalent resistance of parallel combination

$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}$

$\therefore$ $\frac{1}{R_{eq}}=\frac{1}{2}+\frac{1}{5}+\frac{1}{7}$

$\Rightarrow \frac{1}{R_{eq}}=\frac{35+14+10}{70}$

$\Rightarrow R_{eq}=\frac{70}{59}$ $\Omega$