An AM radio station broadcasts isotropically (equally in all directions) with an average power of 3.40 kW. A receiving antenna 60.0 cm long is at a location 4.00 mi from the transmitter. Compute the amplitude of the emf that is induced by this signal between the ends of the receiving antenna.

Respuesta :

To solve the problem we will apply the concepts related to the Intensity as a function of the power and the area, as well as the electric field as a function of the current, the speed of light and the permeability in free space, as shown below.

The intensity of the wave at the receiver is

[tex]I = \frac{P_{avg}}{A}[/tex]

[tex]I = \frac{P_{avg}}{4\pi r^2}[/tex]

[tex]I = \frac{3.4*10^3}{4\pi(4*1609.34)^2} \rightarrow 1mile = 1609.3m[/tex]

[tex]I = 6.529*10^{-6}W/m^2[/tex]

The amplitude of electric field at the receiver is

[tex]I = \frac{E_{max}^2}{2\mu_0 c}[/tex]

[tex]E_{max}= \sqrt{2I\mu_0 c}[/tex]

The amplitude of induced emf by this signal between the ends of the receiving antenna is

[tex]\epsilon_{max} = E_{max} d[/tex]

[tex]\epsilon_{max} = \sqrt{2I \mu_0 cd}[/tex]

Here,

I = Current

[tex]\mu_0[/tex] = Permeability at free space

c = Light speed

d = Distance

Replacing,

[tex]\epsilon_{max} = \sqrt{2(6.529*10^{-6})(4\pi*10^{-7})(3*10^{8})(60.0*10^{-2})}[/tex]

[tex]\epsilon_{max} = 0.05434V[/tex]

Thus, the amplitude of induced emf by this signal between the ends of the receiving antenna is 0.0543V