Birds resting on high-voltage power lines are a common sight. The copper wire on

Question

Birds resting on high-voltage power lines are a common sight. The copper wire on which a bird stands is 2.95 cm in diameter and carries a current of 89 A. If the bird's feet are 8.52 cm apart, what is the potential difference across its body? Copper's resistivity is 1.68 times 10^-8 Ohm m. Answer in units of mu V. A length of metal wire has a radius of 0.001 m and a resistance of 0.06 Ohm. When the potential difference across the wire is 16 V, the electron drift speed is found to be 0.000289 m/s. Based on these data, calculate the density

Explanation / Answer

First calculate the resistance

Resistance of a wire in
R = L/A
is resistivity of the material in -m
L is length in meters
A is cross-sectional area in m²
A = r², r is radius of wire in m
resistivity Cu 17.2e-9 -m

R = 1.68*10^-8*0.0852 / pi*(0.0295/2)^2 = 209.418 ohm

Then use ohm's law, V = IR where I = 89 amps

V = 18638.24 Volt

b) drift velocity Vd
Vd = I / nqA
I is current
n is the number of charge carriers per m³
A is the cross sectional area on m²
q is the charge of the charge carriers
q = –1.602 × 10–19 C

The current you can get from 16/0.06 = 266.667 amps = I

Vd = I / nqA

n = I / Vd*q*A = 266.667 / 0.000289*1.602*10^-19*pi*0.001^2

n = 1.8334*10^30 per m^3

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