Electromagnetic Induction
A changing magnetic flux creates an induced electric response. The induced current acts in the direction that opposes the change in flux that produced it.
How can a magnetic change make charge move without a battery?
Changing magnetic flux creates a circulating electric field. A conducting loop lets that electric field drive a current around the loop.
The minus sign is Lenz's law: the induced response opposes the change in flux.
Change the magnetic field through a loop.
Induction responds to magnetic flux through the loop, so field strength, loop area, orientation, or any combination of them can create a change.
If the induced current reinforced the change that created it, the system could amplify itself without an energy source. The opposing direction prevents that runaway.
Rotating a coil in a magnetic field changes flux periodically, creating alternating emf. Mechanical work becomes electrical energy transfer.
Induced electric fields do not need to begin or end on charge. They form closed loops around changing magnetic flux.
Each loop experiences the same flux change, so a coil with N turns adds the induced emf around all turns.
A large steady magnetic flux produces no Faraday emf by itself. The time variation is the crucial ingredient.