Answers

2016-05-07T10:58:49+05:30
We know that , R = pL/A
Now for wire A , 
R1 = pL1/A1
And for wire B , 
R2 = pL2/A2
Now we are given R1 = 4R2
OR , pL1/A1 = 4pL2/A2
OR , pL1/(
πr²)1 = 4pL2/(πr²)2
Now , if L1 = L2 
So , [πr²]2 = 4[πr²]1
So , r2 = 2r1
Thus the ratio of their radii will be r1/r2 = 1/2
and the area of their cross-section will be A1/A2
                                            =
(πr²)1 / (πr²)2
                                            = [r1]
²/[r2]² = 1²/2² = 1/4

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