Will 12v electromagnet work with a 9v battery?
Yes it will, but as you might expect, it produces a weaker magnetic field.
Well, it might work. If you have other electronics in the circuit they may not function at the lower voltage.
Yes Drak that is true, I am assuming OP meant just a simple power source supplied to an electromagnet.
If the electromaget is somewhere in a circuit which includes other components, transistors or so, they may not work with a lower power supply setup, and the circuit would not function as intended.
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