Question

The effective resistance between points P and Q of the electrical circuit shown in the figure is

• A. $\frac{2Rr}{(R+r)}$
• B. $8R\frac{(R+r)}{(3R+r)}$
• C. 2r + 4R
• D. $\frac{5R}{2}+2r$

Answer 1

The correct option is A

$\frac{2Rr}{(R+r)}$

In a circuit, any circuit element placed between points at the same potential can be removed, without affecting the rest of the circuit.Here, by symmetry,point A,B
and C are at same potential, for any potential difference between P and Q. The circuit can therefore be reduced as shown below

Effective resistance $R_{eq}=\frac{2Rr}{R+r}.$