How does the erase head of a VCR work?
 

When I tested opened VCRs, I noticed that the tape is touching the erase head (EH) even when not recording. I know that tapes do not get erased only by touching this head unless not in recording mode. But how exactly does the EH work? It gets magnetic only when we hit the Record button?

When I started recording in an opened VCR, I did not see any difference on the EH, compared to operations other than recording (e.g. playback). Does this head help in tape transport? That is why it's touched by the tape when not recording?

It uses electric current to create a magnetic field, You don't see anything visually. Look up electro-magnetism if you haven't encountered such thing in school.