Question

Four resistors, each of resistance R and a key K are connected as shown in the figure. The equivalent resistance between points A and B when key K is open, will be :

• A. 4R
• B. $\infty$
• C. $\frac{R}{4}$
• D. $\frac{4R}{3}$

Answer 1

Answer: (B)

$\infty$

Answer 2

When the key K is open, there is no conducting path between points A and B. According to the definition of equivalent resistance, $R_{eq} = \frac{V}{I}$. If there is no path for current to flow between A and B, then $I = 0$ for any applied voltage $V$. This leads to an infinite equivalent resistance.