Question

a piece of wire of resistance 20 ohm is drawn out so that its length is increased to twice its original length calculate the resistance of wire in the new situation​

Answer 1

Answer:

80 Ω

Explanation:

Resistance (R) = [Resistivity (ρ) x Length (L)] / [Area (A)]

Initial Resistance R = ρ (L / A)

After wire is drawn out to twice its original length,

New Length L' = 2L, New Area A' = A/2, New Resistivity ρ' = ρ

New Resistance R' = ρ (L' / A') = ρ (2L / (A/2)) = 4 ρ (L / A) = 4 R

R' = 4 R

New resistance = 4 x Old resistance

New resistance = 4 x 20 Ω = 80 Ω

Remember to use the formula : R' = $n^{2}$ R if the wire is stretched n times