Question

A wire of 3 ohm resistance and 10 cm length is stretched to 30 cm length. Assuming that it has uniform cross sectional, what be its new resistance?

Answer 1

$r = p \times l \div a$
Where r is resistance
p(rho) is specific resistance and a is area of cross-section.

Since r is directly proportional to l, we can say new resistance will also be thrice since length has become thrice

r= 3 ohm x 3 = 9 ohms