Question

Three copper wires of lengths and cross sectional areas are (l, A), (2l, A/2) and (l/2, 2A). Resistance is minimum in(a) wire of cross-sectional area A/2(b) wire of cross-sectional area A(c) wire of cross-sectional area 2A(d) same in all the three cases

Answer 1

Answer:

C) Wire of cross-sectional area 2A

Explanation:

Length and cross-sectional areas of first wire = ( l, A) (Given)

Length and cross-sectional areas of second wire = ( 2l, A/2) (Given)

Length and cross-sectional areas of third wire =  ( l/2, 2A) (Given)

Resistance of wire -

R = R ∝ l/A

For first wire = R1 ∝ l/A = R

For second wire = R2 ∝ ( 2l, A/2) = 4R

For third wire = R3 ∝ ( l/2, 2A) = R/4

Therefore, resistance of wire will be minimum for the third wire. ie, wire of cross-sectional area 2A.

Answer 2

Answer:

this is the correct answers for this question