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Question:

Four resistance 10Ω, 5Ω, 7Ω and 3Ω are connected so that they form the sides of a rectangle AB, BC, CD and DA respectively. Another resistance of 10Ω is connected across the diagonal AC. The equivalent resistance between A and B is

7Ω

10Ω

2Ω

5Ω

Solution:

The equivalent resistance across A and C is
RAC=10||(3+7)=10||10=10×1010+10=5Ω
Now The equivalent resistance between A and B is
RAB=10||(5+5)=10||10=10×1010+10=5Ω