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You want to get an idea of the magnitude of magnetic fields produced by overhead powerlines. You estimate the that a transmission wire is about 11m above the ground. The local power company tells you that the lines operate at 240 kV and and provide a maximum power of 46 MW.
a. Estimate the magnetic field you might experience walking under one such power line.
b. Compare this field to the Earth's field: Bwire/Bearth= ?%

Respuesta :

Answer:

a)[tex]\beta =2.46x10^{-6} T[/tex]

b) B=3.8%

Explanation:

The magnetic field can be find using the equation

[tex]\beta =\frac{u_{o}*I_{o}}{2\pi*d}[/tex]

a).

Now to determinate the current Io knowing the power and the voltage can determinate the current

[tex]P_{max}=I*V[/tex]

[tex]V=V_{rms}*\sqrt{2}[/tex]

[tex]V=240x10^3v*\sqrt{2}[/tex]

[tex]V=339.441 kV[/tex]

[tex]I_{o}=\frac{P_{max}}{V}[/tex]

[tex]I_{o}=\frac{46x10^6W}{339.411x10^3v}[/tex]

[tex]I_{o}=135.5 A[/tex]

Replacing

[tex]u_{o}=4\pi x10^{-7}\frac{T*m}{A}[/tex]

[tex]d=11m[/tex]

[tex]\beta =\frac{4\pix10^{-7}\frac{T*m}{A} *135.5A}{2\pi*11m}[/tex]

[tex]\beta =2.46x10^{-6} T[/tex]

b).

The magnetic field of the earth is about 68uT so compare with this field

%[tex]=\frac{\beta_{wire}}{\beta_{earth}}[/tex]

%[tex]=\frac{2.46uT}{64uT}*100[/tex]

%=3.8 %

A) The estimated magnetic field experienced under such power line; 2.46 * 10⁻⁶T

B) when compared to the earth's magnetic field = 3.8%

Given Data :

Height of transmission wire ( d ) = 11m

voltage of power line ( Vrms ) = 240 kV

Max power in Power line ( Pmax )  = 46 Mw

u₀ = 410⁻⁷ T.m / A

a) Determine the magnetic field of the power line

β = [tex](u_{0}*I_{0} )/ 2\pi d[/tex] ---- ( 1 )

where;  I₀ = Pmax / V  ---- ( 2 )

and     V = Vrms * √2 ---- ( 3 )

Back to equation ( 3 )

V = 240 * 10³ * √2

   = 339.441 kV

Back to equation ( 2 )

I₀ = ( 46 * 10⁶ ) / ( 339.441 * 10³ )

  = 135.5 A

Insert given and calculated values into equation ( 1 )

β = ( 410⁻⁷ * 135.5 ) / (2 * π * 11 )

   = 2.46 * 10⁻⁶ T

B) The ratio of magnetic field produced by wire to Earth's magnetic field

Bwire / Bearth

= 2.46 * 10⁻⁶  / 64 * 10⁻⁶

= 0.038 = 3.8%

Hence we can conclude that The estimated magnetic field experienced under such power line; 2.46 * 10⁻⁶T, when compared to the earth's magnetic field = 3.8%

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