(1) A wire of 9 ohm resistance having 30cm length is tripled on itself.What is its new resistance?
(2) What length of copper wire of resistivity 1.7 x 10 to the power of -8 x ohm metre and radius 1 mm is required so that its resistance is 1 ohm?
Answers
Answered by
21
(2)
p = 1.7 × 10^-8 ohm/m
A = π × 10^-6 m²
R = 1 ohm ,
since ,
R = pl/A
1 = 1.7 × 10^-8 × l / π × 10^-6
π × 10^3 / 17 = l
l = 184.799 m
p = 1.7 × 10^-8 ohm/m
A = π × 10^-6 m²
R = 1 ohm ,
since ,
R = pl/A
1 = 1.7 × 10^-8 × l / π × 10^-6
π × 10^3 / 17 = l
l = 184.799 m
Answered by
48
1) R = 9 Ω L = 30 cm ρ = constant
R' = ? L' = 3 * L
case a)
If the length is tripled ie., multiplied by 3 , then:
R = ρL/A, so R is also multiplied 3 times => R' = 3 R => 27 Ω
case b)
if the wire is folded so that the length becomes L/3 and the area of cross section now becomes 3 times. R' = R *1/3 * 1/3 = R/9 = 1 Ω
=============================================
2)
R = ρ L / A => L = R A /ρ
L = 1 Ω * π * (1 * 10⁻³)² m² / 1.7 * 10⁻⁸ Ω-m
= 184.79 m
R' = ? L' = 3 * L
case a)
If the length is tripled ie., multiplied by 3 , then:
R = ρL/A, so R is also multiplied 3 times => R' = 3 R => 27 Ω
case b)
if the wire is folded so that the length becomes L/3 and the area of cross section now becomes 3 times. R' = R *1/3 * 1/3 = R/9 = 1 Ω
=============================================
2)
R = ρ L / A => L = R A /ρ
L = 1 Ω * π * (1 * 10⁻³)² m² / 1.7 * 10⁻⁸ Ω-m
= 184.79 m
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