Question

What is the equivalent resistance between A and B in the given figure

• A. 40 $\Omega$
• B. 10 $\Omega$
• C. 50 $\Omega$
• D. 20 $\Omega$.

Answer 1

Answer: (D)

20 $\Omega$.

Answer 2

This is a case of balanced wheatstone bridge. Since the resistances in upper and lower arms are in series, therefore equivalent resistance in upper arm $(R)=R_{1}+R_{2}=20+20=40 \,\Omega$ and equivalent resistant of lower arm $R'=R_{3}+R_{4}=20+20=40 \,\Omega$. Now the equivalent resistances $R$ and $R'$ are in parallel. Therefore their resultant resistance $R''=\frac{40 \times 40}{40+40}=\frac{1600}{80}$ $=20 \,\Omega$