Question no . 51 .If a copper wire is stretched to make its radius decrease by .1% then the percentage increase in its resistance is approximately ????1. .1%2. .2%3. .4%4. .8%

Here volume remains constant so,resistance become inversely proportional to area.as area is proportional to r square.by applying %changes,we get that change in 1% in radius changes resistance about 4% but inversely proportional to each other