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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, 7 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! · 1 year, 7 months ago

Thanks for your help. · 1 year, 7 months ago

You are welcome! · 1 year, 7 months ago

Answer should be 0.2%. · 1 year, 7 months ago

@Calvin Lin ,@Chung Kevin ,@Nihar Mahajan , @Mehul Arora ....plz help!!! · 1 year, 7 months ago

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% · 1 year, 7 months ago

Thanks...you really helped me! · 1 year, 7 months ago

Always welcome brother! :) · 1 year, 7 months ago

Well....i am a girl. ;) · 1 year, 7 months ago