Question 451: Current Electricity

Question

The length of a given cylindrical wire is increased to double of its original length. The percentage increase in the resistance of the wire will be ____________ %.

Accepted Answer

Volume is constant so on length doubled
Area is halved so
$$R = ho {l \over A}$$ and $$R' = ho {{2l} \over {{A \over 2}}} = 4ho {l \over A} = 4R$$
So percentage increase will be
$$R\%  = {{4R - R} \over R} 	imes 100 = 300\% $$

Current Electricity

The length of a given cylindrical wire is increased to double of its original length. The percentage increase in the resistance of the wire will be ____________ %.

Choose the correct answer: