Equivalent resistance between A and B in Fig. is

Options

A. 8r/7
B. 7r/8
C. 3r/4
D. r

Answer

B

Explanation

The figure can be redrawn as shown. Connect a battery between
A and B. Now `R_(eq) = V//I`

in ACEA, `I_(1)r = (I -2I_(1))/(2) r +(I - 2I_(1))r or 3I = 8I_(1)`
In FACBGF, `V = I_(1)r + (I)/(2)r = (3)/(8)Ir +(I)/(2)r =l (7r)/(8)I`
or `R_(eq) = (V)/(I) = (7r)/(8)`