According to given circuit diagram When switch is open, then combination
R1 and
R2 will be in series and also combination
R3 and
R4 will be in series and these branches will be in parallel.
∴ Equivalent resistance
(Req )===RWhen switch is closed, then combination
R1 and
R3 will be in parallel and also, combination
R2 and
R4 will be in parallel. After that, both will be in series.
∴ Equivalent resistance,
(R′eq)=+=+ =+=Now, dividing Eq. (i) by Eq. (ii), we get
c== x=9