Magnetic Fields vs Electric Fields

The terms magnetic field and electric field are often thrown around haphazardly without understanding exactly what the differences are between them. This is not surprising; magnetic fields and electric fields are complex phenomena that act similarly in some ways. Though this is true, they are not the same things and need to be understood separately, as well as how they work when combined.

The magnetic field is used to describe the influence of magnetism on a point in space. There are some materials in our world, typically metals, that will attract one another physically when you put them close together. Others will repel each other. In physical magnets, magnetic fields are caused by certain materials while other materials are unaffected by the phenomena. If a material is not affected by magnets, it is considered a non-magnetic material. Some examples of these are wood, plastic, paper, glass, and rubber.

Similarly, in electrical circuits, we have electric fields that can exist around electric objects. An electric field describes the influence of electricity on a point in space. There are particles that exist within matter that will repel and attract one another, just as there are particles that will be completely unaffected. Materials that are not affected by charged particles are considered insulators, while those affected are called conductors.

So what’s the difference then? Electricity and Magnetism are often thrown together in the same bucket because one can affect the other, but there are some materials that are conductive (experiencing electric force) but not magnetic (not having atoms aligned in a way that allows magnetic domains to line up). Both are a result of charged particles in the atoms that make up matter. In a copper conductor, a string of charged particles moving in a direction is said to be an electrical current. This current carries an electric field that moves with the particles. It is an electric field, rather than a magnetic one because the moving charged particles are electric objects interacting with each other through the electric fields that exist between the particles. This field is inside of the conductor, existing between and around the charged particles. A byproduct of the movement of these particles and their electric fields is that a magnetic field is produced around the conductor. It’s a completely separate thing from the electric field inside the conductor.

Magnetic field surrounding a magnet
Electric field surrounding a charged particle

The interesting thing about this copper conductor is that copper does not have enough lined-up magnetic domains to be magnetic, itself. So while the copper conductor will not attract to a magnet simply by touching one to it, a magnetic effect can be achieved around the conductor by passing an electric current through the conductor, resulting in an electric field within the conductor as well as a magnetic field around the conductor.

It’s not just conductive objects that we find may not also be magnetic, there are magnetic objects that are not electrically conductive, though less common. These are called magnetic insulators and usually refer to materials that have some type of “magnetic order” that allows a magnetic attraction, but still act as an electrical insulator, disallowing electrical current flow in the material.

A magnetic field is generated in a material that has a certain alignment or relative grouping of charged particles along the length of the material. We call these small “pockets” of alignment, magnetic domains, or magnetic moments. When enough of these magnetic domains line up in the same direction the entire material experiences a magnetic field through, and around it. When they’re not aligned, the material will not manifest a magnetic effect. It has nothing to do with the material’s ability to conduct electric current, as the individual electrons in the material may or may not still be able to flow. Some materials can be “magnetized” by introducing them to a magnetic field which, essentially, forces the magnetic domains to line up. Other materials can have magnetic domains that simply won’t line up by passing them through a magnetic field. These objects are non-magnetic, and cannot be changed to become magnetic.

Left: Magnetic domains aligned – Right: Magnetic domains not aligned – Source: researchgate.net

An electric field will have a difference of electrical potential between one side of the field and the other, which represents the force, or pressure, which exists between the two sides. Connecting the two sides of the field together with a conductor will make electrically charged particles flow from one side to the other in an effort to balance out. This movement of charges is what we call electric current, and we use it to do work. A magnetic field will not have a difference of electrical potential between one side of a magnet and the other. A magnetic force is simply an effect that allows attraction and repulsion between objects but does not create a flow of electrical current between two magnetic objects. Electrical current flow is a result of a build-up of opposing electrical charge between two separate conductive objects.

Magnetic Fields

What is the fundamental quanta, or smallest particle, that makes up a magnet? A magnetic monopole is a hypothetical particle (or class of particles) that has, as its name suggests, only one magnetic pole (either a magnetic north or south pole). In other words, it would possess a “magnetic charge” analogous to an electric charge. Similar to an electric charge, it gains true importance only when its opposite charge is present to interact with.

This is fun to think about, however, magnetic charges have never been observed in isolation. On the contrary, every isolated magnetic charge discovered was found attached to another magnetic object with two poles. Magnetic monopoles cannot exist in magnetic fields because magnetic poles of opposite polarity attract one another. This, along with the fact that magnetic monopoles have never been observed, means the magnetic charge is always found in dipole form.

Opposite magnets attract
Like magnets repel

How a magnetic field works is by attracting magnetic poles of the same polarity and repelling magnetic poles of opposite polarity. This is done through magnetic forces, which are stronger than electric forces that attract oppositely charged magnetic poles.

A magnetic dipole is capable of exerting a magnetic field to form a “magnetic circuit” with other magnetic components including other magnetic dipoles. Every magnet has lines of force around it that extend from pole to pole. We call these lines of force, flux lines, and say magnets have varying amounts of magnetic flux, depending on the materials they’re made of. A magnetized object, if small enough, will have a magnetic field similar in shape to its size. Depending on the shape and where the north and south pole is placed, it can create different patterns or magnetic fields around it. The important thing to understand is that magnetic fields are invisible, yet they are observable when creating an interaction between two different magnets. And the real separator from electric fields is that electrical potential (voltage) will not exist between the north and south poles of a magnet, but it will exist between positive and negative electric charges.

Electric Fields

Next, we can look at the fundamental quanta of electric charge, the electron, proton, and a few other subatomic particles within the atom. Just like a magnet, one of these alone doesn’t have anything noteworthy to observe, however, when another charge similar or opposing polarity is introduced you’ll notice an invisible field between them similar to that of a magnet. We don’t call this a magnetic field, we call it an electric field – even though it can interact with magnetic fields, and acts similarly to attract and repel.

Dissimilar charges attract
Like charges repel

Charged particles contain either a positive electric charge or a negative electric charge. Just as with magnets, there are lines of flux around the particles, and the more charges we stack together the greater the overall electric flux we can achieve in the electric field around the conductor. Stacking up charges on one side of a field, and opposing charges on the other side of the field is what gives us a difference of electrical potential, or what we call voltage. When we physically connect the two sides with a conductor, electric current will flow through the conductor. Meaning the charges will leave the original object, travel through the conductor to the other side of the original object, acting to discharge the build-up of charges back to an even amount of charge throughout the system.

Both electric fields and magnetic fields can influence the movement of electric charges in an electric circuit. Both can also influence a magnetic field in a magnet. Where they differ, however, is in the way the fields operate. Since an electric charge is a single object or monopole, and a magnet is a dipole (excluding the aforementioned theoretical monopole idea) the fields around the objects behave differently. A magnet has a field around the entire object, leaving one end and traveling to the other. A charge will have a field either only “pushing outward” or “pulling inward,” depending on if it is a positive or negative charge.

The Electric Field only interacts with other charged objects – much like the magnetism of a permanent magnet only interacts with other magnetic materials. They seem so similar, that one could confuse them for the same thing. When we back up and view them from far above we realize that moving a magnet near an electrical charge will make the charge move, because a magnetic field can interact with an electric field around a charged particle. Also moving a charged particle near a magnet will allow the electric field around the charged particle to interact with the magnetic field around the magnet. However, no electric current is transferred from the magnet to the conductor, nor from the conductor back to the magnet. The electric current only exists within the electric conductor, which if it is copper, is a non-magnetic material.

One more important observation is to note that a magnetic field moving near an electric field, will cause the electric charges to move, but only while the magnet continues to move. If you were to move the magnet close to the conductor and just keep it held to the conductor, the charges would balance back out and return (relatively) back to where they started. So a moving magnetic field can influence an electric field. Similarly, a static electric field will not produce a magnetic field around a conductor, but a moving electric field will. The relationship to motion as a way to transfer mechanical energy from a magnetic field to electrical energy in an electrical field, and back again – is how all electrical systems work.

An electrical system, after all, is simply a spinning magnet at a utility company generator that continually spins near electrical conductors. This moving magnetic field contains mechanical energy from the mechanical machine doing the spinning. This mechanical energy is only able to become electrical energy once it interacts with the electric field in the conductors around the magnets. The mechanical energy transfers to electrical energy inside the conductor and travel all the way to the load at our homes. Once the electrical energy reaches a home, it is either disbursed through resistive loads in the electric circuit, or it is transferred back into mechanical objects with magnets in them, like ceiling fans or anything else with motors. In the case of a fan motor, the electrical energy is transferred from the electric circuit back into mechanical energy via the interaction with a magnetic field inside the motor and begins to spin the blades of the fan. Important to note, if the spinning magnet at the utility stops, the magnet is still near the conductors in the generator, but we won’t have current flow in the system. Similarly, if the movement of electric charge in a conductor stops, there will be no transference of energy from the electric circuit to the motor, and it will not spin – even though the conductors are near the fan motor. Motion is the key to the energy-exchange relationship between magnetic and electric fields.

Leave a Reply

Your email address will not be published.

Back to top button