Physics, 13.10.2019 18:10 tiadenae22ovtxdr

Birds resting on high-voltage power lines are a common sight. the copper wire on which a bird stands is 1.28 cm in diameter and carries a current of 149

a. if the bird's feet are 4.12 cm apart, what is the potential difference across its body? copper's resistivity is 1.68 × 10−8 ω m . answer in units of µv.

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Answer from: fanta47

$8\cdot 10^{-4} V$

Explanation:

First of all, let's find the cross-sectional area of the copper wire. The radius of the wire half the diameter:

$r=\frac{d}{2}=\frac{1.28 cm}{2}=0.64 cm=6.4\cdot 10^{-3} m$

So the area is

$A=\pi r^2 = \pi (6.4\cdot 10^{-3} m)^2=1.29\cdot 10^{-4} m^2$

Now we can calculate the resistance of the piece of copper wire between the bird's feet, with the formula:

$R=\rho \frac{L}{A}$

where

$\rho=1.68\cdot 10^{-8} \Omega m$ is the resistivity of copper

$L=4.12 cm=4.12 \cdot 10^{-2} m$ is the length of the piece of wire

$A=1.29\cdot 10^{-4} m^2$ is the cross-sectional area

Substituting, we find

$R=(1.68\cdot 10^{-8} m^2)\frac{4.12\cdot 10^{-2} m}{1.29\cdot 10^{-4} m^2}=5.4\cdot 10^{-6} \Omega$

And since we know the current in the wire, I=149 A, we can now find the potential difference across the body of the bird, by using Ohm's law:

$V=IR=(149 A)(5.4\cdot 10^{-6} \Omega)=8\cdot 10^{-4} V$

Answer from: Quest

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.

Answer from: Quest

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

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