The radar system at an airport broadcasts 11 GHz microwaves with 150 kW of power. An approaching airplane with a 30 m2 cross section is 30 km away. Assume that the radar broadcasts uniformly in all directions and that the airplane scatters microwaves uniformly in all directions.

What is the electric field strength of the microwave signal received back at the airport 200 \mu s later? Express your answer in μV/m.

=___________ μV/m

- I'm not sure if the 11 GHz or 200 μs is necessary in the problem or not. All the examples I've looked at that are similar to this problem don't include those two values in their calculations.

Respuesta :

Answer:

[tex]7.516\cdot 10^9 \mu V/m[/tex]

Explanation:

The relationship between the power of an electromagnetic wave and the amplitude of its electric field is given by the equation:

[tex]P=\epsilon_0 E^2 c[/tex]

where

P is the power of the wave

[tex]\epsilon_0[/tex] is the vacuum permittivity

E is the amplitude of the electric field

c is the speed of light

In this problem we have:

[tex]P=150 kW = 1.5\cdot 10^5 W[/tex] is the power of the microwaves

[tex]\epsilon_0 = 8.85\cdot 10^{-12}} F/m[/tex] is the vacuum permittivity

[tex]c=3.0\cdot 10^8 m/s[/tex] is the speed of light

Solving for E, we find:

[tex]E=\sqrt{\frac{P}{\epsilon_0 c}}=\sqrt{\frac{1.5\cdot 10^5}{(8.85\cdot 10^{-12})(3.0\cdot 10^8)}}=7516 V/m =7.516\cdot 10^9 \mu V/m[/tex]

The strength of the amplitude electric field received back at the airport is [tex]1.9407 \times 10^ 9\ \mu V/m[/tex].

The given parameters;

  • frequency of the wave, f = 11 GHz
  • power of the wave, P = 150 kW
  • area of the airplane, A = 30 m²

The relationship between wave Intensity (I), Power (P), area (A), amplitude electric field strength (E₀), and speed of light(c) is given as follows;

[tex]I = \frac{P}{A} = \frac{c\times \epsilon _0\times E_o^2 }{2} \\\\c\times \epsilon _o\times E_o^2 \times A = 2P\\\\E_o^2 = \frac{2P}{A \times c \times \epsilon _o} \\\\E_o = \sqrt{\frac{2P}{A \times c \times \epsilon _o}} \\\\E_o = \sqrt{\frac{2\times 150,000}{(30) \times (3\times 10^8) \times (8.85\times 10^{-12})}} \\\\E_o = 1940.74 \ V/m\\\\E_o = 1.9407 \times 10^ 9\ \times 10^{-6}\ V/m\\\\E_o = 1.9407\times 10^ 9 \ \mu \ V/m[/tex]

Thus, the strength of the amplitude electric field received back at the airport is [tex]1.9407 \times 10^ 9\ \mu V/m[/tex]

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