Question

35.
The masses of the three wires of copper
are in the ratio of 1: 3: 5. And their
lengths are in the ratio of 5:3 : 1. The
ratio of their electrical resistance is :
(a) 1:3:5
(b) 5:3:1
(c) 1:15: 125 (d) 125: 15:1​

Answer 1

Explanation:

let v1,v2and v3 are their volumes and density

of copper= d

length are L1,L2,L3 and radius of cross section

are R1,R2and R3 respectively

=> m1:m2:m3= v1d:v2d:v3d= 1:3:5

=> v1:v2:v3= 1:3:5

=> πR1²L1 : πR2²L2 : πR3²L3= 1:3:5

=>5 R1²:3R2²:R3²= 1:3:5

=> R1² : R2² : R3² = 1 : 9 : 25

=> ratio of resistances

=> 5/1 : 3/9 : 5/25= 5 : 1/3 : 1/5

=> 75 : 5 : 3