Electromagnetic Field Theory
A rectangular waveguide is a

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

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Electromagnetic Field Theory
Magnetostriction is a phenomenon of

 change in physical dimensions of ferromagnetic materials during magnetism.
 generation of electricity in ferromagnetic materials.
 generation of magnetism in electrical conductors.
 change in permeability of ferromagnetic materials during magnetism.

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