In balanced condition, in a Wheatstone bridge,
‌=‌ Given,
P=5Ω,Q=10Ω If
40Ω resistor is connected across
S arm, then net resistance offered by this arm is
Snet‌‌=‌ =20Ω Now, in order to balance the bridge again,
10Ω resistor has to connected across
Q, so the net resistance offered by
Q‌net ‌ will be
5Ω.
So, the new balanced condition will be
‌=‌ ⇒ ‌=‌