The equivalent resistance between point A and B with swich `S` open and closed are resistance

Options

A. `4 Omega,8 Omega`
B. `8 Omega,4 Omega`
C. `6 Omega,9 Omega`
D. `9 Omega,6 Omega`

Answer

b

Explanation

When swich `S` is poened the equivalent circuit will be

The equivalent resistance between `A` and `B` is
`R_(eq) = (12 xx6)/(12+6) + (6xx 12)/(6+12) = 4 + 4 = 8 Omega`
When swich `S` is closed , the equivalent circuit will be The equivalent resistance between `A` and `B` is
`R'_(eq) = ((4+4)xx8)/((4+4)+8) = 4 Omega`