V.K. Sally Solutions for Chapter: Electricity, Exercise 6: Practice Problems : 3

A resistance wire made from German silver has a resistance of $4.25\mathrm{\Omega }$. Calculate the resistance of another wire, made from same material, such that its length increases by four times and area of cross-section decreases by three times.

A nichrome wire of length $l$ and area of cross-section $\frac{a}{4}$ has a resistance $R$. Another nichrome wire of length $3l$ and area of cross-section $\frac{a}{2}$ has resistance of $R_1$. Find the ratio of  $R_1:R$.

A $4\mathrm{\Omega }$ resistance wire is doubled on it. Calculate the new resistance of wire.

[Hint: On doubling: length becomes $1/2$ and area of cross-section becomes double]