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As shown in the circuit diagram find the value of I ________.

Asked in GUJCET 2024 · Wheatstone bridge

Figure: Wheatstone bridge
Answer: (2) 2.5 A

Step-by-step solution

Given: from the figure AB=2 Ω, BC=4 Ω, AD=4 Ω, DC=8 Ω, a galvanometer of 10 Ω between B and D, and a cell of 10 V across A and C.

Idea: before combining anything, test the bridge for balance. (AB)/(BC)=2/4 and (AD)/(DC)=4/8, and both equal 1/2.

The bridge is balanced, so B and D sit at the same potential and no current crosses the 10 Ω galvanometer branch. It can be left out of the sum.

Two paths then join A to C in parallel: 2+4=6 Ω through B, and 4+8=12 Ω through D.

R=(6×12)/(6+12)=4 Ω, so I=(10)/4=2.5 A.

Why the other options are wrong

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