Question

A copper wire is stretched to increase its length by 1%. Then the change in its resistance is close to ______.

Options

• 1%

• 4%

• −4%

• 2%

Answer 1

A copper wire is stretched to increase its length by 1%. Then the change in its resistance is close to 2%.

Explanation:

Given: `(Delta L)/L` = 1%

= 0.01

Since volume is constant:

LA = constant

⇒ A ∝ `1/L`

So,

`(Delta A)/A` = −1%

Use percentage change in resistance:

R ∝ `L/A`

`(Delta R)/R = (Delta L)/L - (Delta A)/A`

= 1% − (−1%)

= 1% + 1%

= 2%