Question

. A wire in drawn such that its radius changes from r to 2 r. The new resistance is
(a) 1 time
(b) 4 times
(c) 8 times
(d) 1/16 times
The answer is d 1/16 . can anyone explain how??
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Answer 1

Answer:

d option is correct R= resistivity×length /area but if area change length is also affected without affecting length new formula for such type qs are R is directly propotional to 1/A^2 and A=πr^2 so Ris directly propotional to 1/r^4