Electromagnet would emit light? Light is an Electomagnetic wave. When I create an electromagnet by passing electricity wound around a core and keep changing the electric field, does it emit photons?
Is the frequency of electromagnetic radiation equals the frequency of change in the electric field? If yes can it emit visible light if the frequency is in that range?
 A: Your question seems to be partly about light and photons.  Light, of course, consists of photons.  But any electromagnetic wave consists of photons; it's just that some photons carry very little energy (at low frequency and long wavelength) and some carry a lot of energy (at high frequency and short wavelength). When the current through an electromagnet is changing, the electromagnetic field is changing, so waves  - photons - are emitted; but the emitted photons are very low frequency and certainly not visible light photons.
A: Technically, yes, that's how a radio works. Although for a radio there is a systematical modulation of the electricity (and the electromagnet).
A: 
When I create an electromagnet by passing electricity wound around a core and keep changing the electric field, does it emit photons?

What you let pass through a wire are electrons and this electrons are moving in circles (along a spiral path) through the wire. When electrons are moved in circles they underlying an acceleration and by this emit photons. Furthermore electrons in a wire do not moving in straight lines, they get bounced on other subatomic particles and during these accelerations emit photons. As longer is the free path for their acceleration as higher is the velocity before the bounce and the harder the braking the higher energy photons get emitted. Sometimes Bremsstrahlung leads to photon emission in the range of X-rays.

Is the frequency of electromagnetic radiation equals the frequency of change in the electric field? If yes can it emit visible light if the frequency is in that range?

An alternating current will modulate the above mentioned EM radiation. But the photons in this EM radiation are of different frequency. But of course were is correlation is the raise in the emitted energy in dependence from the frequency of the alternating current.
