I had a query in th following question:

A given wire of resistece is stretched to double its length. What will be its new resistance?

How come the answer is 4 ?

Asked by rohanraval2 | 28th Mar, 2020, 09:22: PM

Expert Answer:

ρ= RA/l
R = ρl/A
When length is doubled l =2l and area of cross section is reduced to half
ρ is constant for wire.
 
Thus,
ρ = R'(A/2)/(2l)
ρ= R'A/(4l)
Thus,
R' = 4(ρl/A)
R'= 4R 
 
Thus, when length is doubled then resistance becomes 4 times its original value. 

Answered by Shiwani Sawant | 28th Mar, 2020, 10:25: PM