Calculate equivalent resistance between P and Q.

A metallic wire carries a current of $1$ Ampere. Calculate

(i) Charge 

(ii) The number of electrons crossing the cross-section of the wire in $1$ second.

The resistance of a wire of length $90 \mathrm{cm}$ is found to be $20 \mathrm{\Omega }$. The area of the cross-section of the wire is $4\times {10}^{-5} {\mathrm{m}}^2$. Find the specific resistance of the material of the wire.

Name a substance used for making connecting wire and why.

If a wire of length $1 \mathrm{m}$ and resistance $10 \mathrm{\Omega }$ is stretched until its length becomes $3 \mathrm{m}$. What is its new resistance?