Question

Find new resistance of wire if it is stretched to twice its

original length. Original resistance was 20 ohm. Also how its
resistivity will change

Answer 1

Original Length = L1

Stretched length =L2

From

R = pl/A

R=Resistance

p=Resistivity

A=Cross-sectional Area

l= length of wire

We can see that Resistance is directly Proportional to Length... Meaning that Resistance Increases also as Length increases.

R1/L1 = R2/L2

From the question... The key to note is this sentence

"The Stretched length is TWICE the Original Length"

Meaning

L2 = 2L1 (So replace L2 as 2L1 when solving)

R1=20ohms

Let R2 = k

Applying the formula

20/L1 = k/2L1

kL1 = 20x 2 L1

KL1 = 40L1

L1 cancels on both sides

k=40ohms.

So As the length doubled... The Resistance did too

from 20ohms to 40ohms