Question

What is the resistance between A and B in the figure:

• A.
• B. 20 $\Omega$
• C. 40 $\Omega$
• D. 50 $\Omega$

Answer 1

Answer: (A)

Answer 2

It is balanced Wheatstone bridge. Hence, C and D are at same potential so CD arm is uneffective. So, $10\,\Omega$ . resistance in CD arm is uneffective. Now upper arms having resistances $10\,\Omega$ are connected in series. So their equivalent resistance is ${{R}_{U}}=10+10=20\,\Omega$ Similarly the equivalent resistance of lower arm which are also connected in series, so ${{R}_{L}}=10+10=20\,\Omega$ Now ${{R}_{U}}$ and ${{R}_{L}}$ are connected in parallel the resistance between AB is ${{R}_{AB}}=\frac{20\times 20}{20+20}=\frac{400}{40}=10\,\Omega$