CGPET 2021 Solved Paper

Given, resistance of arms as follows

P=9Ω,Q=11Ω,R=4Ω,S=6Ω
Consider resistance (r) is connected to parallel to the resistance (S).
So, that, the bridge is balance.
If r' be the equivalent resistance of r and S, then
⇒

1

r′

=

1

S

+

1

r

⇒(

S.r

S+r

)
Bridge is balanced, if

P

Q

=

R

S

⇒

P

q

=

R

(S. r S +r)

=

R(S+r)

Sr

⇒

9

11

=

4(6+r)

6r

Solving, r=

132

5

Ω