Question : A wire of a certain material is stretched slowly by ten percent. Its new resistance and specific resistance become respectively.
a) both remain the same.
b) 1.1 times, 1.1 times
c) 1.2 times, 1.1 times
d) 1.21 times, same.
[AIPMT, 2011]
Doubt by Manasvini
Solution :
We know , When the length of a wire is stretched by n times then its new resistance is given by n2R
R'=n2R
ATQ
L' = L + 10% of L
L' = L + 0.1L
L' = 1.1L
Hence, the wire is stretched by 1.1 times.
So New Resistance will be
R'=n2R
R'=(1.1)2R
R'=1.21R
The Resistivity of a wire depends only on the nature of the material and not on the dimensions of the wire like length.
Hence the resistivity of the wire will remain same.
Therefore, d) 1.21 times, same, would be the correct option.
