# 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
5 years 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!

- 5 years ago

You are welcome!

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%

- 5 years ago

Thanks...you really helped me!

- 5 years ago

Always welcome brother! :)

- 5 years ago

Well....i am a girl. ;)

- 5 years ago

Sorry, Sister* :P

- 5 years ago