Final answer:
An electromagnet placed in a magnetic field will rotate to align with that field, much like a compass needle aligns with the Earth's magnetic field. This is due to the interaction between the magnetic fields, which causes a torque on the electromagnet.
Step-by-step explanation:
When an electromagnet is placed within an external magnetic field, it will rotate to align with the field. This is similar to the behavior of a compass needle in the Earth's magnetic field. The alignment occurs because the magnetic field produced by the electromagnet interacts with the external field, causing a torque on the electromagnet. The underlying principle that explains this behavior is also used in electric motors, where an electromagnet (the rotor) inside a magnetic field rotates as electric current flows through it.
In contrast to the other options provided, the electromagnet does not vibrate to create sound, and it does not remain inactive until the current is turned off. These behaviors are not characteristics of an electromagnet's interaction with a magnetic field. Lastly, the electromagnet does not rotate to align opposite to the field; instead, it seeks to minimize magnetic potential energy by aligning with the magnetic field lines, much like two magnets would align with each other when brought into close proximity.