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Question

A metallic wire of resistance R is melted and recast to half of its original length while maintaining the original volume. What will the new resistance of the wire be?


A

R4

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B

R2

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C

4R

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D

2R

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Solution

The correct option is A

R4


Volume of the metallic wire = L×A

Let and A are the original length and area of cross-section respectively.

Let l' and A' be the corresponding values of length and cross sectional area on recasting.

Al=Alor ll=AA

ll=12(Given)AA=12

Now, R=ρlA (Original resistance)

New resistance, R=ρlA

RR=ρlAρlA

=(ll)(AA)
=(12)(12)=14
or R=R4


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