When a charge is accelerated its said that it produces electromagnetic waves. They also say that an accelerating charges produces time changing electromagnetic field and which when passes through a conductor induces voltage in it. I wonder are these two terms same ? Electromagnetic waves is the concept used in communication while electromagnetic field/induction is the concept mostly used in motors,transformers and generators. Please explain. I am confused on it.
The basic distinction here is between "field" and "wave". An EM wave is a radiation of power. That radiation contains an electric and a magnetic field content. Both fields are in phase and, together they have a ratio of 377 in a vacuum. Without the phase alignment or the correct amplitude ratio they don't travel very far but can (if the circumstances are favourable) form a coherent EM wave such as at about one wavelength distant from a correctly made radio antenna.
Why 377 ohms?
Thats the impedance of free-space governed by the square root of the ratio of magnetic permeability to electric permeability: -
The term "electromagnetic field" is looser and could be used to mean or imply: -
- EM wave (due to it time changing as per the question title)
- Near fields around an antenna
- The magnetic field caused by an electric field