COMEDK Exam 2014 Solved Paper

For first copper wire,
l1=1m
For second copper wire, l2=9m
We have to find, diameter ratio of two wires, i.e.

d1

d2

=?
Since, both copper wired have same resistances.
i.e. R1=R2
⇒ ρ.

l1

A1

=ρ.

l2

A2

(∵R=ρ.

l

A

)
⇒

l1

( πd12 4 )

=

l2

( πd22 4 )

⇒

l1

d12

=

l2

d22

⇒

d1

d2

=√

l1

l2

=√

1

9

=

1

3

‌or‌1:3