Imagine an electromagnet. If you have a high current and low voltage vs a low current and high voltage which will create a stronger magnetic field? I understand the low current high voltage has to have a higher resistance but imagine it has a way of changing without changing the number of windings or anything else.
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The strength of magnetic field depends entirely on current. In the idle state (when the magnet doesn’t actively attract or repel things), the voltage is parasitic – it is only used to fight with the resistance of the material. All consumed energy is wasted on heat – the magnetic field itself does not require “upkeep”. In superconductors, it is possible to have current with 0 voltage – so superconductor electromagnets do not require voltage or energy to keep a magnetic field up.
The things get different, when the things get moving in the magnetic field. When the magnet speeds up some object – it experiences **counter-electromotive force voltage (counter EMF)**. This voltage will act against the current, reducing it, as well as the strength of the field. You have to actively *increase* the voltage, if you want to keep the strength the same. Even superconductor electromagnets will require a voltage in this case – therefore, they will consume energy.
When the electromagnet slows down things, it experiences the opposite effect – **forward EMF**. The magnet will become a source of voltage – you can connect it to the grid, and it will generate electricity.
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