CBSE - X - Physics - Electricity
use the formual R = ρ L / A , where R is resistance, ρ is resistivity ,L is lenght of wire, A is area of crossesection.
use the formula for both the cases in one put the value of L = L and area = πr2 and in second case put the value of L=2L and area = π(2r)2 , for series combination add the resistance from above.and find the ratio,
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