What are Magnets & Electromagnets? | Physics for EmSAT Achieve PDF Download

How do magnets function?

• The functioning of magnets is fundamentally attributed to the movement of electrons. When an electric charge is in motion, it generates a magnetic field. Therefore, magnets and magnetic fields are closely interconnected. In an atom, the orbital motion of electrons around the nucleus, being charged particles, generates a small magnetic field. However, in most materials, the presence of numerous electrons cancels out the magnetic fields created by individual electrons, resulting in no overall magnetism from the material.
• Nevertheless, certain materials behave differently. The magnetic field produced by one electron can influence the alignment of the magnetic fields generated by neighboring electrons, causing them to align. This leads to the formation of magnetic "domains" within the material, where all the electrons have aligned magnetic fields. Materials exhibiting this behavior are known as ferromagnetic materials. At room temperature, only iron, nickel, cobalt, and gadolinium exhibit ferromagnetic properties. These materials have the capability to become permanent magnets.
• The domains within a ferromagnetic material exhibit random orientations, meaning that while neighboring electrons align their fields, other groups may be aligned in different directions. Consequently, on a larger scale, the presence of different domains cancels out the overall magnetism, similar to how individual electrons do in other materials.
• However, when an external magnetic field is applied, such as by bringing a bar magnet close to the material, the domains begin to align. As all the domains align, the entire material effectively becomes a single domain and develops two poles, commonly referred to as north and south (though positive and negative can also be used).
• In ferromagnetic materials, this alignment persists even after the external field is removed. In contrast, other materials, known as paramagnetic materials, lose their magnetic properties once the external field is no longer present.

What are the characteristics of a magnet?

• Magnetism is characterized by its ability to attract certain materials and the opposite poles of other magnets while repelling like poles. For instance, when two permanent bar magnets are brought together with two north (or south) poles facing each other, a repulsive force occurs, which intensifies as the ends get closer. Conversely, when opposite poles, one north and one south, are brought together, an attractive force is observed, growing stronger as they are brought closer.
• Ferromagnetic materials like iron, nickel, cobalt, or alloys containing them, such as steel, are attracted to permanent magnets, even when they are not generating a magnetic field themselves. However, they are only attracted to magnets and will not be repelled unless they start producing their own magnetic field. Other materials like aluminum, wood, and ceramics are not attracted to magnets.

How Does an Electromagnet Function?

• An electromagnet differs significantly from a permanent magnet as it relies on the presence of electricity and is essentially formed by the movement of electrons through a wire or conductor. Similar to the formation of magnetic domains, the flow of electrons through a wire generates a magnetic field. The shape of this field depends on the direction of electron movement—by pointing the thumb of your right hand in the current direction, your fingers curl in the direction of the field.
• To create a basic electromagnet, an electrical wire is coiled around a central core, typically made of iron. When electric current passes through the wire, circulating around the core, a magnetic field is produced along the central axis of the coil. This magnetic field exists regardless of whether a core is present, but with an iron core, it aligns the domains within the ferromagnetic material, making the field stronger.
• When the flow of electricity ceases, the electrons stop moving within the wire coil, causing the magnetic field to dissipate.

What Are the Characteristics of an Electromagnet?

Both electromagnets and permanent magnets share essential properties. The distinction between them lies in how the magnetic field is generated, not in the properties of the field itself. Therefore, electromagnets exhibit two poles, attract ferromagnetic materials, and experience repulsion between like poles while attracting unlike poles. The difference lies in the fact that the moving charge in permanent magnets arises from the motion of electrons within atoms, whereas in electromagnets, it originates from the movement of electrons as part of an electrical current.

Advantages of Electromagnets

• Electromagnets offer numerous advantages. One of the key benefits stems from the fact that the magnetic field is generated by the flow of electric current, allowing for flexibility in its characteristics. By adjusting the current, the strength of the magnetic field can be increased or decreased accordingly. Additionally, using alternating current (AC electricity) enables the creation of a continuously changing magnetic field, which is useful for inducing currents in neighboring conductors.
• In applications like magnetic cranes used in metal scrap yards, electromagnets possess a significant advantage: the ability to easily switch off the magnetic field. If a large permanent magnet were used to lift a piece of scrap metal, detaching it from the magnet would prove challenging. In contrast, with an electromagnet, simply stopping the current flow causes the scrap metal to be released.

Magnets and Maxwell's Laws

• Maxwell's laws describe the principles of electromagnetism. While these laws are expressed using vector calculus and involve complex mathematical concepts, the fundamental principles underlying magnetism can be grasped without delving into intricate mathematics.
• The first law, known as the "no monopole law," states that all magnets exhibit two poles, and the existence of a single pole in isolation is impossible. In other words, a magnet cannot have a north pole without a corresponding south pole, and vice versa.
• The second law, Faraday's law, explains the process of induction. It describes how a changing magnetic field, produced either by an electromagnet with varying current or by a moving permanent magnet, induces a voltage (and electric current) in a nearby conductor.
• The final law, the Ampere-Maxwell law, illustrates how a changing electric field generates a magnetic field. The strength of the field is determined by the current passing through an area and the rate of change of the electric field, which is caused by charged particles such as protons and electrons. This law is employed to calculate magnetic fields in simpler scenarios, such as in a wire coil or a straight wire.