Question

the resistance of a wire is 20 ohm it is stretched so that the length becomes doubled then the new resistance of the wire will be

please solve this problem​

Answer 1

Answer:

80 ohm

Explanation:

As we knew that the resistance is directly proportional to the length. So, if we double the length of the wire, the resistance of the wire will also be doubled.

20×2= 40

now the resistance is 40 ohm

and we knew that resistance is inversely proportional to the diameter of the wire. if we stretch the wire to double the length of the wire, it's diameter will remains to half. here, we halved the diameter of the wire so again resistance will be doubled.

40×2 = 80 ohm

finally the resistance of the wire is 80 ohm

Answer 2

Answer:

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Explanation:

Given,

R = 20 Ω  

$Let,Length\:of\:wire\:is\:L\:and\:when\:it\:Drawn\:out,\:its\:New\:Length\:is\:2L$

The volume of wire in both the situations remains constant.So, it the length of wire doubled, the area of cross section of wire becomes half.

$So,\:The\:New\:Resistance\:of\:Wire-$

$R_{new}  = \frac{2l}{(A/2)}$

$=\frac{4L}{A}$

$=4\:\times\:Old\:resistance\:of\:wire........(Because, R=L/A)$

$= 4\:\times\: 20$  

=  80 Ω