An EM wave radiates outwards from a dipole antenna, with E0 as the amplitude of its electric field vector. The electric field E0 which transports significant energy from the source falls off as
Given
Amplitude of electric field vector = E0
Explanation:
We know that, the intensity of radiation is given,
Where W is the energy emitted by the bulb, t is the time, and A is the area on which the radiation is incident.
Therefore, assuming the energy and time to be constant we have,
An antennae radiates energy in a spherical shape around it, thus A=4πr2.
We , know that the electric field and average intensity or energy are related as
Therefore, the energy from the source falls of as 
.
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