In this blog post, we’ll explore how everyday electrical appliances—such as electric fans and washing machines—convert electrical energy into rotational motion, and examine the principles behind motors through the relationship between electric current and magnetic fields.

Motors That Convert Electrical Energy into Rotational Motion

You’ve probably turned on a fan on a hot summer day. You’ve likely also run a washing machine to do laundry. When electrical energy is supplied to a fan or a washing machine, the internal motor rotates, driving the fan blades and the washing drum, respectively. As such, there are many devices around us that convert electrical energy into mechanical energy—specifically, rotational motion—for practical use. One of the core components of these devices is the motor. An electric motor is a device that converts electrical energy into rotational mechanical energy, and its basic principle lies in the interaction between electric current and magnetic fields. When a conductor carrying an electric current is placed within a magnetic field, it experiences a force, and the motor uses this electromagnetic force to generate rotational torque.

Why does a magnetic field form when an electric current flows?

You may recall from elementary school observing a compass needle move when an electric current was passed through a wire. This phenomenon demonstrates that a magnetic field forms around a wire through which an electric current flows. Electric current and magnetic fields are closely related; an electric current—consisting of moving charges—creates a magnetic field around it.
To understand this relationship more easily, let’s use the analogy of a stream of water. When a current flows through a wire arranged in a circle, a magnetic field forms around it. You can think of this as a stream of water—the magnetic field—gushing out from the center of a thin, circular pipe made of current. Of course, a real magnetic field is not a substance that moves like flowing water but rather a field formed in space; however, this analogy helps us understand that the strength of the magnetic field varies depending on the magnitude of the current. Generally, under the same conditions, as the current increases, the magnetic field it generates also becomes stronger.

If we adjust the direction and magnitude of the electric current, will the direction of the magnetic field also change?

Now, let’s consider two pipes. Suppose pipe a is oriented so that the stream of water flows to the right, and pipe b is oriented so that the stream of water flows downward. Now, let’s arrange the two pipes so that they share the same center and imagine what happens when the two streams of water merge. We can expect that the stream flowing to the right and the stream flowing downward will interact to create a combined stream directed to the lower right. If we make Pipe A thicker so that the stream flowing to the right becomes stronger, and make Pipe B thinner so that the stream flowing downward becomes weaker, the combined stream will be directed almost entirely to the right. Conversely, if Pipe A were made thinner and Pipe B were made thicker, the combined stream would point almost entirely downward. In other words, if we could adjust the intensity of the streams coming from the two pipes as desired, we could create streams pointing in various directions between the right and downward directions. By adjusting the effects acting from multiple directions in this way, we can envision effects pointing in various directions relative to the center of the circle.
Now, let’s consider the relationship between electricity and magnetism. Earlier, we analogized the pipes to conductors through which current flows, the thickness of the pipes to the strength of the current, and the water jets to magnetic fields. Therefore, we can conclude that by arranging multiple current-carrying conductors in appropriate directions and adjusting the current in each, we can generate a magnetic field in the desired direction. In actual electric motors, the magnitude and direction of the currents flowing through multiple coils are appropriately controlled to create a rotating magnetic field or to cause the magnetic fields of the rotor and stator to interact with each other. In particular, in alternating current (AC) motors, a rotating magnetic field can be generated by utilizing the phase difference between the alternating currents flowing through the various coils.

How can a magnetic field be represented?

Let’s briefly explore what a magnetic field is. A magnetic field is generated by magnets or electric currents, and magnetic field lines are often used to illustrate the direction and magnitude of the force exerted by the magnetic field on an object. Magnetic field lines around a magnet are generally depicted as emanating from the N pole and entering the S pole on the outer surface of the magnet. Therefore, rather than simply understanding the arrows of the magnetic field lines as “starting at the N pole and ending at the S pole,” it is more accurate to view them as a representation of the direction in which the magnetic field is formed around the magnet.
If we revisit the analogy of a pipe and a stream of water used earlier, we can think of the direction of the water stream as representing the direction of the magnetic field. However, it is important to distinguish that an actual magnetic field is not a phenomenon where a substance flows in one direction, like a stream of water, but rather a physical field formed in space.

Will a motor move if the magnetic field is rotated?

If so, what does it mean to be able to continuously change the direction of the magnetic field? In an electric motor, the design ensures that the magnetic field generated by a current-carrying coil interacts with the magnetic field of a permanent magnet or another electromagnet. In this case, the forces—whether attractive or repulsive—between the two magnetic fields act as torque that drives the rotor. Therefore, if the direction of the magnetic field is changed sequentially, the rotor can continue to rotate in response to those changes.
Let’s consider this in simpler terms. Suppose there is a disk with a magnet attached to it, and a coil carrying an electric current around it generates a magnetic field. By appropriately varying the current flowing through the coil, attractive and repulsive forces arise between the magnet on the disk and the magnetic field generated by the coil. When these forces act at a point away from the center of the disk, a rotational force is generated that causes the disk to rotate. Subsequently, by appropriately changing the direction or intensity of the current flowing through the coil to continuously alter the direction of the magnetic field, the disk can continue to rotate in one direction.
The key point here is that simply repelling one N-pole against another N-pole, or one S-pole against another S-pole, once is not enough to create sustained rotational motion. For the motor to continue rotating, the direction of the magnetic field must be continuously adjusted to match the position of the rotor. In a brushed DC motor, the direction of the current is reversed via the commutator, while in a brushless motor, electronic control is used to sequentially switch the current flowing through the coils. In an AC motor, torque is generated through the interaction between the rotating magnetic field created by the alternating current and the rotor.

Is a rotating disk actually a motor?

Now, let’s use this to consider how a motor rotates. A current-carrying coil generates a magnetic field, and if this magnetic field is configured to interact with the rotor’s magnetic field, a rotational force is generated on the rotor. This rotational force causes the rotor to turn, and if a shaft is connected to the rotor, that rotational force can be transmitted to another device. Actual motors use this principle to convert electrical energy into rotational motion. The basic operating principle of an electric motor lies in electromagnetic force—the force exerted on a current-carrying conductor within a magnetic field—and by applying this force at the appropriate location, rotational torque is generated.
We have explained the principles of motors so far. In summary, a current-carrying coil generates a magnetic field, and this magnetic field interacts with other magnetic fields to produce a force. Electric motors utilize this force as rotational torque. Although the operating methods and structures vary depending on the type of motor, they all fundamentally generate rotational motion through the interaction between electricity and magnetism.
For example, in a permanent magnet motor, the magnetic field generated by the permanent magnets interacts with the magnetic field generated by the current-carrying coils to produce rotational force. In an AC induction motor, the rotating magnetic field of the stator induces a current in the rotor, and the resulting magnetic field interacts with the stator’s magnetic field, causing the rotor to move.
The rotational motion generated in this way is utilized in a variety of machines. When a fan blade is attached to the motor’s shaft, it becomes an electric fan; when connected to a washing machine’s drum or related drive mechanism, it provides the power that drives the washing machine. In this way, many of the electrical appliances we commonly use in our daily lives convert electrical energy into rotational motion via a motor and utilize that rotational motion according to the specific purpose of each appliance.