Class 12 NEET Physics Current Electricity Questions Part 1

Resistance of a wire,R=ρ

l

A

=4Ω.....(i)
When wire is stretched twice, its new length be I′. Then
l′=2l
On stretching volume of the wire remains constant.
∴lA=l′A′ where A′ is the new cross-sectional area
or A′=

l

l′

=A=

l

2l

A=

A

2

∴ Resistance of a stretched wire is
R′=ρ

l′

A′

=ρ

2l

( A 2 )

=4ρ

l

A

4(4Ω)=16Ω  (Using (i))