Birds can safely stay on high voltage power lines without being electrically sho
ID: 3896148 • Letter: B
Question
Birds can safely stay on high voltage power lines without being electrically shocked. A 100kV power line has a cable diameter d of 1.5 cm, and is made of copper with resistivity of 1.72x10^-8 ?m
a) What is the cross-sectional area of the cable in m^2? Hint: The cross-sectional area of a cylinder is
A= (?/4) d^2
b) A bird has its feet spacing of 3cm. Consider a short section of cable with the same length. What is the resistance of this section of cable?
c) The current flowing through the cable can be as high as 2000 Amperes. What is the voltage across the short section of cable? Do you think that poses a life threat the bird?
Explanation / Answer
a) Area
= (pi/4) d^2
= (3.14/4) * (1.5 * 0.01)^2
= 1.766 * 10^-4 m^2
b) Resistance
= pl/A
= 1.72 * 10^-8 * 0.03 / (1.766 * 10^-4)
= 2.92 * 10^-6 ohm
c) V = IR
V = 2000 * 2.92 * 10^-6
V = 5.84 mV
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