Electromagnetism

We explain what electromagnetism is and what some of its applications are. Also, its history and examples.

What is electromagnetism?

Electromagnetism is the branch of physics that studies the relationships between electrical and magnetic phenomena that is, the interactions between charged particles and electric and magnetic fields.

In 1821 the foundations of electromagnetism were made known with the scientific work of the British Michael Faraday, which gave rise to this discipline. In 1865, the Scot James Clerk Maxwell formulated the four “Maxwell equations” that completely describe electromagnetic phenomena.

See also: Electrostatics

Applications of electromagnetism

Electromagnetic phenomena have very important applications in disciplines such as engineering, electronics, health, aeronautics or civil construction, among others. They appear in daily life, almost without us realizing it, in compasses, speakers, doorbells, magnetic cards, hard drives.

The main applications of electromagnetism are used in:

• The electricity.
• The magnetism.
• Electrical conductivity and superconductivity.
• Gamma rays and X-rays.
• Electromagnetic waves.
• Infrared, visible and ultraviolet radiation.
• Radio waves and microwaves.

Experiments on electromagnetism

Through simple experiments it is possible to understand some electromagnetic phenomena, such as:

The electric motor. To do an experiment that demonstrates a basic notion of the operation of an electric motor, we need:

• • a magnet
  • One AAA battery
  • a screw
  • A piece of electrical cable 20 cm long
• First step Place the tip of the screw on the negative terminal of the battery and place the magnet on the head of the screw. You can see how the elements attract each other due to magnetism.
• Second step Join the ends of the cable with the positive pole of the battery and with the magnet (which is together with the screw, on the negative pole of the battery).
• Result The battery-screw-magnet-cable circuit is obtained through which an electric current flows through the magnetic field created by the magnet, and it rotates at high speed due to a constant tangential force called the “Lorentz force”. On the contrary, if you try to join the pieces by reversing the poles of the stack, the elements repel each other.

The Faraday cage Below is an experiment that allows us to understand how electromagnetic waves flow in electronic devices. For this, the following elements are needed:

• • A battery-operated portable radio or cell phone
  • A metal grid with holes no larger than 1 cm
  • Pliers or scissors to cut the grille
  • Small pieces of wire to join the metal grill
  • Aluminum foil (may not be necessary)
• First step Cut a rectangular piece of metal mesh 20 cm high by 80 cm long, so that a cylinder can be assembled.
• Second step Cut another circular piece of metal mesh 25 cm in diameter (it should be large enough to cover the cylinder).
• Third step Join the ends of the metal mesh rectangle so that a cylinder is formed and secure them with pieces of wire.
• Fourth step Place the radio on inside the metal cylinder and cover the cylinder with the metal mesh circle.
• Result The radio will stop playing because the electromagnetic waves from outside cannot pass through the metal.
  If instead of a radio on you insert a cell phone and call that number to make it ring, it will not ring. If it rings, you should use a thicker metal grill with smaller holes, or wrap the cell phone in aluminum foil. Something similar happens when you talk on your cell phone and enter an elevator, which causes the signal to be cut off, which is the “Faraday cage” effect.

What is electromagnetism used for?

Electromagnetism is very useful for humans since there are countless applications that allow them to satisfy their needs. Many instruments used daily work due to electromagnetic effects. The electric current that circulates through all the connectors in a house, for example, provides multiple uses (the microwave oven, the fan, the blender, the television, the computer) that operate due to electromagnetism.

Magnetism and electromagnetism

Magnetism is the phenomenon that explains the force of attraction or repulsion between magnetic materials and moving charges.

Electromagnetism involves physical phenomena produced by electrical charges at rest or in motion, which give rise to electric, magnetic or electromagnetic fields, and which affect matter that can be in a gaseous, liquid or solid state.

Examples of electromagnetism

There are numerous examples of electromagnetism and among the most common are:

• The bell. It is a device capable of generating an audible signal when pressing a switch. It works through an electromagnet that receives an electric charge, which generates a magnetic field (a magnet effect) that attracts a small hammer that impacts against the metal surface and emits a sound.
• The magnetic levitation train. Unlike the train driven by an electric locomotive that advances on rails, this is a means of transportation that is supported and propelled by the force of magnetism and by the powerful electromagnets located in its lower part.
• The electrical transformer. It is an electrical device that allows the voltage (or tension) of an alternating current to be increased or decreased.
• The electric motor. It is a device that converts electrical energy into mechanical energy, producing movement through the action of the magnetic fields generated inside it.
• The dynamo It is an electrical generator that uses the mechanical energy of a rotating movement and transforms it into electrical energy.
• The microwave oven. It is an electric oven that generates electromagnetic radiation at the microwave frequency. These radiations make the water molecules in the food vibrate, which produces heat quickly, cooking the food.
• The MRI. It is a medical examination through which images of the structure and composition of an organism are obtained. It consists of the interaction of a magnetic field created by a machine, the magnetic resonator, (which works like a magnet), and the hydrogen atoms contained in the person's body. These atoms are attracted by the “magnet effect” of the device and generate an electromagnetic field that is captured and represented in images.
• The microphone. It is a device that detects acoustic energy (sound) and transforms it into electrical energy. It does this through a membrane (or diaphragm) that is attracted by a magnet within a magnetic field and that produces an electric current that is proportional to the sound received.
• Planet Earth. Our planet works like a giant magnet due to the magnetic field generated in its core (made up of metals such as iron and nickel). The rotation of the Earth generates a stream of charged particles (the electrons of the atoms in the Earth's core). This current produces a magnetic field that extends several kilometers above the planet's surface and repels harmful solar radiation.

History of electromagnetism

• 600 BC c The Greek Thales of Miletus observed that when rubbing a piece of amber, it became charged and was able to attract pieces of straw or feathers.
• 1820 The Danish Hans Christian Oersted carried out an experiment that for the first time united the phenomena of electricity and magnetism. It consisted of bringing a magnetized needle close to a conductor through which an electric current was circulating. The needle moved in a way that showed the presence of a magnetic field in the conductor.
• 1826 The Frenchman André-Marie Ampère developed the theory that explains the interaction between electricity and magnetism, called “electrodynamics”. Furthermore, he was the first to name electric current as such and to measure the intensity of its flow.
• 1831 The British physicist and chemist, Michael Faraday, discovered the laws of electrolysis and electromagnetic induction.
• 1865 The Scot James Clerk Maxwell unveiled the foundations of electromagnetism by formulating the four “Maxwell equations” that describe electromagnetic phenomena.

Continue with: Faraday's Law

References

• «What is histology?» in Ivy Roses.
• “Histology” in Wikipedia.
• “Histology” in Wikipedia.
• «Tissue Classification» in Biological Sciences.
• «Electromagnetism» in Wikipedia.
• «What is electromagnetism for?» at Karen Linda.
• “What does a microphone do?” in Audio Technica.
• «Electromagnetism» in Madrid.
• “Faraday's Cage” (video) on Educacciontv.
• “A Brief History of Electromagnetism” in Nusgrem.