A copper wire of resistance 4W is melted and redrawn to thrice its original length. Find the resistance of stretched wire.
40 W
60 W
45 W
36 W
As we learnt
Stretching of wire -
If a conducting wire stretches it's length increases area of cross-section decreases but volume remains constant.
- wherein
Since volume of the wire does not change.
Þ l1A1 = l2 A2 where l1 and A1 are the initial length and cross-section of the wire, and l2 and A2 are the final length and cross-section.
Þ . . . (1)
and
Þ . . . (2)
Þ
as l2 = 3l1
Þ R2 = 9R1 = (9 ´ 4)W = 36 W
Option 1)
40 W
Option 2)
60 W
Option 3)
45 W
Option 4)
36 W
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