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What should be the answer?

If length of a conducting wire is increased by \(0.1\)%, the the resistance will increase by how much percentage?

A. \(2\)%


B. \(0.2\)%


C. \(1\)%


D. \(0.1\)%

Note by Sahba Hasan
1 year, 9 months ago

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Resistance of a wire depends inversely on area of cross section and directly on length of wire. But, since volume of wire remains constant, an increase in length causes a decrease in area. Dividing the new length by new area obtained, we get the new resistance.Subtract 1 from this and then multiply by 100.This will give you the %.The calculation is not long, but it involves big numbers like 1000 and 1001(even their squares!).Use difference of 2 squares rule(HINT).Calculate, and u will get the answer very close to 0.2(actually, 0.2001). Sorry, couldn't show the calculation here! Anibrata Bhattacharya · 1 year, 9 months ago

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@Anibrata Bhattacharya Thanks for your help. Sahba Hasan · 1 year, 9 months ago

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@Sahba Hasan You are welcome! Anibrata Bhattacharya · 1 year, 9 months ago

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Answer should be 0.2%. Anibrata Bhattacharya · 1 year, 9 months ago

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@Calvin Lin ,@Chung Kevin ,@Nihar Mahajan , @Mehul Arora ....plz help!!! Sahba Hasan · 1 year, 9 months ago

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@Sahba Hasan First, Thanks for mentioning me, Though I don't deserve that honour :)

Then, When a wire is stretched by x%, Then resistance will increase by 2x%. but this is applicable only x<10 (I don't know why, though)

Thus the answer should be 0.2% Mehul Arora · 1 year, 9 months ago

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@Mehul Arora Thanks...you really helped me! Sahba Hasan · 1 year, 9 months ago

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@Sahba Hasan Always welcome brother! :) Mehul Arora · 1 year, 9 months ago

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@Mehul Arora Well....i am a girl. ;) Sahba Hasan · 1 year, 9 months ago

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@Sahba Hasan Sorry, Sister* :P Mehul Arora · 1 year, 9 months ago

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