Assume the local public radio station kuaf radiates 5w of power in radio waves uniformly in all directions (in a uniform sphere). (a)what is the intensity of the waves at 1km = 1000m from the station? (b)what is the maximum amplitude of the electric field at 1km from the station? (c)what is the maximum amplitude of the magnetic field at 1km?

To solve this problem it is necessary to apply the equations related to intesity of plane electromagnetic wave, velocity of Speed, area of a Sphere and the permittivity of free space.

For definition we know that Intensity is equal to,

Where,

P = Power

A = Area (At this case sphere)

PART A) Using this definition the Intensity would be,

PART B) To calculate the maximum amplitud of electric field we can use the definition the intesity of plane electromagnetic wave, that is

Where,

Constant of permittivity of free space

c = Speed of light

Amplitude of the electric field

Replacing we have that,

Re-arrange to find

PART C) The amplitude of the magnetic field would be given by

Where,

 Amplitude of the electric field

c = Speed of light

Replacing,

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the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.