A wire P has half the diameter and half the length of a w...
A wire P has half the diameter and half the length of a wire Q of similar material. The ratio of the resistance of P to that of Q is
8 : 1
4 : 1
2 : 1
1 : 1
1 : 4
Correct answer is C
Resistance α lengtharea
RQRP = LQAPLPAQ
LQ = 2LP
DQ = 2DP
AP = π(2DP)22
= πDP
AQ = π(DP)22
= 14πDP
therefore, RQRP = 2LP×πDPLP×14πDP
= 2 : 1
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