Answer:
R' = R/2
Therefore, the new resistance of the wire is twice the value of the initial resistance.
Explanation:
Consider a wire with:
Resistance = R
Length = L
Area = A = πr²
where, r = radius
ρ = resistivity
Then:
R = ρL/A
R = ρL/πr² --------------- equation 1
Now, the new wire has:
Resistance = R'
Resistivity = ρ
Length = L' = 2 L
Radius = r' = 2r
Area = πr'² = π(2r)² = 4πr²
Therefore,
R' = ρL'/πr'²
R' = ρ(2 L)/4πr²
R' = (1/2)(ρL/πr²)
using equation 1:
R' = R/2
Therefore, the new resistance of the wire is twice the value of the initial resistance.
