Question

A metallic wire will have the lowest resistance in which of the following cases ( l= length of the wire , d = diameter of the wire )
1 point
(a) l , d
(b) 2l , d
(c) l/2 , 2d
(d) 2l , d/2​

Answer 1

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12th

Physics

Current Electricity

Electrical Resistance & Resistivity

A piece of copper is to be ...

PHYSICS

A piece of copper is to be shaped into a conducting wire of maximum resistance. The suitable length and diameter are __________ and __________ respectively.

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VIDEO EXPLANATION

ANSWER

Resistance of copper wire R=ρ

A

L

where ρ is the resistivity of the material of wire and is constant.

Area of the wire A=

4

πd

2

⟹ R=k

d

2

L

where k=

4

ρπ

= constant

(A) : R

A

=k

d

2

L

(B) : R

B

=k

(d/2)

2

2L

=8

d

2

kL

(C) : R

C

=k

(2d)

2

L/2

=

8

1

d

2

kL

(D) : R

D

=k

d

2

2L

=2

d

2

kL

Hence dimensions of copper wire given in option B has the maximum resistance