Sreshtha asked:
“A piece of wire is redrawn without any change in volume so that its radius become half the original. Compare the new resistance with the original value.”
Answer:
When we redraw the wire, the volume remains constant and the resistivity also remains constant. SO, the variables are
- area of cross section and
- the length
When radius becomes half, the area of cross section increases in such a way that A1l1 = A2l2. This implies that when length is halved, area of cross section is doubled.
We know that 
Therefore, the new resistance becomes (1/4) th the original value.
So, R2:R1 = 1:4
