Electromagnetic Field Theory
A rectangular waveguide is a

Hollow rectangular conducting tube through which electromagnetic waves can be propagat-ed
Tube antenna to transmit and receive electromagnetic waves
Hollow rectangular walled room carrying electromagnetic wave
Rectangular conducting wire to propagate electromagnetic waves

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Electromagnetic Field Theory
According to Coulomb’s law, the force of attraction or repulsion, between to electrical charges is

 directly proportional to the square of the distance between them.
 directly proportional to the distance between them.
 inversely proportional to the square of the distance between them.
 inversely proportional to the distance between them.

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