Question

Please answer Q15,,please

Answer 1

resistance,R = resistivity ×l/a
here a=pie×r^2
now lenth is doubled so
length of another wire=2l
area of another wire= pie ×r^2/4 =a/4

so resistance of another wire
= resistivity × 2l/a/4
=resistivity ×8l/a
=8R [ because r= resistivity ×l/a]

Answer 2

option D is correct

R = resistivity*L/A
= resistivity*L/pi*r^2
now if L =2L and r=1/2r
then
R=resistivity*2L/pi*r^2*1/4
=8*resistivity*L/pi*r^2
=8R
hence D is correct