Question

A wire of resistance 3ohm is stretched to twice its original length. The resistance of the new wire will be (A) 1.5 ohm (B) 3 ohm (C) 6 ohm (D) 12ohm​

Answer 1

Answer:

Explanation:

There is no material gained or lost. Assuming absolutely even stretching, with the length doubled, the cross-sectional area must be halved since volume = length x area.

With half of the cross-sectional area, the ohms-per-foot doubles. It is as if you’ve split the wire lengthwise.

But the length has doubled, so double that resistance.

Therefore the final resistance is 4 x 3 ohms = 12 ohms.

You can do this more simply for any stretching factor by multiplying the original resistance times the square of the stretching factor.