Question

A piece of wire of resistance R is drawn to double its length . The new resistence is
i) R
ii) 2R
iii) 4R
iv) R/4
Please help me in this question...​

Answer 1

Answer:

ii) 2R

Explanation:

We know that

Specific resistance is the resistance offered by a conductor per unit length and per unit area of cross - section.

Where,

R = Resistance

A = Area

L = Length

p = rho

R ~ L

R ~ 1/A

Then,

R = p × L / A ....... (i)

Now it is given, that length is doubled then, new resistance = R',

R' = p × 2L / A

=> R' = 2 × p × L / A ..... (ii)

From equation (i) and equation (ii), we get,

=> R' = 2 × R

Hence, the required answer = ii) 2R

Answer 2

Answer:

Option(iii)

Explanation:

Given Resistance of a wire

R = pL/A

On doubling length by stretching :

L' = 2L

A' = A/2

∴ R' = pL'/A'

     = p(2L)/A/2

    = 4pL/A

   = 4R

Hope it helps!