Sawaal
2
Q:

A copper wire of radius r and length lhas a resistance of R. A second copper wire with radius 2r and length lis taken and the two wires  are  joined  in  a  parallel  combination. The  resultant  resistance   of  the  parallel combination of the two wires will be

A) 5 R B) 5 R/4
C) 4 R/5 D) R/5

Answer:   D) R/5



Explanation:

1st copper wire: R = pl/A = pl/ πr2

2ndcopper wire: R’ = p’l’/A’ = pl/(4 πr2) = R/4

If joined in parallel, (1/Req) = (1/R) + (1/R’)

= 1/R + 4/R1/Req= 5/R

Req= R/5

Subject: Physics
Exam Prep: Bank Exams
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