The equivalent resistance of the circuit across `AB` is given by
.

Options

A. `4Omega`
B. `13Omega`
C. `4Omega` or `13Omega`
D. `4Omega` or `0Omega`

Answer

C

Explanation

When both junction diodes are forward biased, their effective resistance becomes zero. The circuit lift is a balanced Wheatone bridge, whose effective resistance between A and B
`=((2+4)xx(4+8))/((2+4+(4+8)=4 Omega`
When both the junction diode are reverse biased, their effective resistance becomes infinite. The effective resistance between `A` and `B`
`=4+5+4=13 Omega`