Q. A copper wire of resistance $R$ is cut into ten parts of equal length. Two pieces each are joined in series and then five such combinations are joined in parallel. The new combination will have a resistance
A) $R$
B) $\frac{R}{4}$
C) $\frac{R}{5}$
D) $\frac{R}{25}$
Explanation
(d) $R \propto l$
Hence every new piece will have a resistance $\frac{R}{10}.$ If two pieces are connected in series, then their resistance $= \frac{2R}{10} = \frac{R}{5}$
If 5 such combinations are joined in parallel, then net resistance $= \frac{R}{5 \times 5} = \frac{R}{25}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.