When people think of magnets, they usually picture either a permanent magnet, like a refrigerator magnet that retains its force indefinitely, or an electromagnet, which is a temporary magnet powered by an electric current. Despite their distinct mechanisms of operation—one relying on material properties and the other on electrical input—both types function to achieve the same physical result. Understanding how these two seemingly different devices operate reveals a deep unity in the laws of physics that govern them.
The Universal Nature of Magnetic Fields
The most immediate similarity between an electromagnet and a permanent magnet lies in the invisible influence they project into the space around them, known as a magnetic field. This field is the medium through which magnetic force is transmitted to other objects. Scientists visualize this influence using imaginary magnetic field lines, which represent the direction and strength of the force at any point.
In both types of magnet, these field lines follow an identical pattern: they emerge from one end of the magnet and loop around to enter the other end. This field pattern is similar whether created by a current flowing through a coil of wire or by the internal structure of a magnetized piece of metal. This consistency means that a compass needle will react to an electromagnet exactly the same way it reacts to a permanent bar magnet of similar shape and strength.
The magnetic field is the agent that attracts ferromagnetic materials like iron, nickel, and cobalt. The identical response of these materials to either a permanent magnet or an electromagnet confirms the universal nature of the field they produce.
Shared Characteristics of Polarity and Force
All magnets, whether permanent or temporary, share the characteristic of having two distinct magnetic poles, universally designated as North and South. The magnetic field lines always flow from the North pole and curve back to enter the South pole, establishing an inseparable dipole structure.
This polarity dictates how magnets interact, a behavior summarized by the universal laws of magnetic force. Like poles (North facing North or South facing South) will repel each other. Conversely, opposite poles (North facing South) will invariably attract.
This fundamental rule applies without exception to the poles of both electromagnets and permanent magnets. If an electromagnet’s North pole is positioned near a permanent magnet’s North pole, they will repel with predictable force. This identical force dynamic confirms that both devices generate the same basic magnetic structure.
The attractive force also extends to unmagnetized ferromagnetic materials. These materials are temporarily magnetized by either type of field, always inducing the opposite pole closest to the magnet, resulting in attraction.
The Microscopic Source of Magnetism
A key similarity between all forms of magnetism is found at the subatomic level, where the ultimate source of all magnetic fields is the movement of electric charge. Any moving electric charge generates a magnetic field. This unifying principle means that both an electromagnet and a permanent magnet are fundamentally products of moving electrons.
In an electromagnet, this charge movement is macroscopic: a current is deliberately forced through a coiled wire by an external power source. This large-scale, directed flow of electrons through the conductor creates the collective magnetic field that surrounds the entire coil. The strength of the resulting magnetic field is directly proportional to the rate and amount of this electron flow.
In a permanent magnet, the movement is microscopic and inherent to the material’s atomic structure. Within the atoms of ferromagnetic materials, electrons are constantly in motion, both orbiting the nucleus and spinning on their axis. These internal motions constitute tiny, persistent electric currents, each generating a minuscule magnetic field.
The material’s internal structure allows the magnetic fields of countless individual atoms to align within small regions called magnetic domains. This internal alignment of microscopic electron motions, rather than an external current, results in the net, persistent magnetic field. Therefore, whether the charge is flowing down a wire or moving within an atom, the magnetic field is always a consequence of moving charge.
Fundamental Differences in Creation and Control
While the resulting magnetic field and its behavior are identical, the process of creating and controlling the two types of magnets is where their differences become apparent. The magnetic field of an electromagnet is generated by an external electric current, meaning it can be instantly turned on or off with a switch. This reliance on an external energy source makes its magnetism temporary.
This dependence also grants electromagnets a high degree of control, allowing their strength to be varied by simply changing the amount of current flowing through the wire. Furthermore, the poles of an electromagnet can be reversed instantly by switching the direction of the current. In contrast, a permanent magnet’s field is inherent to its material structure and remains fixed without any external power input.
The strength of a permanent magnet is fixed at the time of its manufacture and cannot be adjusted easily. Its polarity is also fixed and cannot be reversed without applying an extremely powerful external field. This fundamental difference in their source—external current versus internal material structure—defines their suitability for various technological applications.