Question

In Wheatstone's bridge $P = 9$ohm, $Q = 11$ohm, $R = 4$ohm and $S = 6$ohm. How much resistance must be put in parallel to the resistance $S$ to balance the bridge

• A. 24 ohm
• B. $\frac { 44 } { 9 }$ohm
• C. 26.4 ohm
• D. 18.7 ohm

Answer 1

Answer: (C)

26.4 ohm

Answer 2

$\frac { P } { Q } = \frac { R } { S ^ { \prime } }$ (For balancing bridge)

⇒ $S ^ { \prime } = \frac { 4 \times 11 } { 9 } = \frac { 44 } { 9 }$

⇒ $\frac { 1 } { S ^ { \prime } } = \frac { 1 } { r } + \frac { 1 } { 6 }$

⇒ $\frac { 9 } { 44 } - \frac { 1 } { 6 } = \frac { 1 } { r }$

⇒ $r = \frac { 132 } { 5 } = 26.4 \Omega$