Question

At a distance of 60.0km from a radio station antenna the electric-field amplitude is 8.70�10^?2V/m

Part B

Assuming that the antenna radiates equally in all directions (which is probably not the case), what is the total power output of the station? in W

Part C

At what distance from the antenna is the electric-field amplitude equal to half the value given? in km

Answer 1

To resolve this prroblem you have to know about Poynting vector

Step 1:

Definition:

Poynting vector: Represents the directional energy flux density (the rate of energy transfer per unit area) of anelectromagnetic field. The SI unit of the Poynting vector is the watt per square metre (W/m²).

Irradiance: irradiance is the radiant flux received by a surface per unit area.

Step 2:

ANSWERS:

B.- Assuming that the antenna radiates equally in all directions (which is probably not the case), what is the total power output of the station? in W

Solve 60 km to meters

In electromagnetism, is defined the irradiance as the value of the energetic intensity, average of an electromagnetic wave at a given point and is calculated as the average value of the Poynting vector.

To calculate the power is necesary get the irradiance , which you get by following equation:

Where

• ?₀ is the vacuum permeability;
• E is the electric field;
• c is the speed of light

C.- At what distance from the antenna is the electric-field amplitude equal to half the value given? in km

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