Question

a wire of resistance 3ohm, 15cm length stretched to 45cm ,find new cross sectional area,new resistance , resistivity Assume wire has uniform cross sectional area

Answer 1

The resistance of the conductor is directly proportional to its length and inversely proportional to its cross sectional area.

So when the wire is streched to tripled its length ,then its  new length =  3l     (where l is the original length)

  New cross sectional area of the wire = A/3 

  Hence ,new resistance,Rn = (3l ) / (A/3)

       Rn = 9R     where R is the original resistance

Thus ,the new resistance will be four times he original one

Therefore Rn = 9 X 3 = 27 Ohm