A metallic wire of resistance R is melted and recast to half of its original length while maintaining the original volume. What will the new resistance of the wire be?
R4
Volume of the metallic wire = L×A
Let and A are the original length and area of cross-section respectively.
Let l' and A' be the corresponding values of length and cross sectional area on recasting.
Al=A′l′or l′l=AA′
l′l=12(Given)∴AA′=12
Now, R=ρlA (Original resistance)
New resistance, R′=ρl′A′
∴R′R=ρl′A′ρlA
=(l′l)(AA′)
=(12)(12)=14
or R′=R4