Electromagnet facts for kids
An electromagnet is a special kind of magnet. Unlike a regular magnet that is always "on," an electromagnet only works when electric current flows through it. When the current is turned off, the magnetic power disappears!
Electromagnets are usually made from a wire wound into a coil. When electricity passes through this wire coil, it creates a magnetic field right in the middle of the coil. Often, this wire is wrapped around a piece of iron or a similar material. This "core" helps to make the magnetic field much stronger.
The best thing about electromagnets is that you can control their strength. You can make them stronger or weaker by changing how much electricity flows through the wire. You can also turn them on and off very quickly. However, they need a constant supply of electricity to stay magnetic, unlike permanent magnets which don't need power.
Electromagnets are used in many everyday devices. You can find them in motors, generators, loudspeakers, hard disks, and even MRI machines in hospitals. In factories, huge electromagnets are used to pick up and move heavy metal objects like scrap iron.
Some very large electromagnets need special electronic systems to control their power. These systems change the electric current slowly to prevent sudden power surges. It can even take several minutes for a huge magnet to fully turn on or off! Also, some powerful electromagnets need water cooling systems to remove the heat they produce.
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How Electromagnets Were Discovered
The first electromagnet was invented in 1824 by a British scientist named William Sturgeon. He took a horseshoe-shaped piece of iron and wrapped about 18 turns of bare copper wire around it. Back then, wires weren't insulated, so he varnished the iron to stop the electricity from escaping.
When Sturgeon connected a battery to his coil, the iron became magnetic and could pick up other metal pieces. When he disconnected the battery, the magnetism disappeared. His first electromagnet was small, weighing only about 200 grams (7 ounces), but it could lift an amazing 4 kilograms (9 pounds)! Sturgeon's magnets were not super strong because he could only wrap a single layer of wire around the core.
Later, starting in 1830, an American scientist named Joseph Henry made electromagnets much better. He used wire that was insulated with silk thread. This allowed him to wrap many layers of wire around the iron core, creating incredibly powerful magnets. Some of Henry's magnets could lift hundreds of pounds! The first important use for these stronger electromagnets was in telegraph sounders, which sent messages over long distances.
What Are Electromagnets Used For?
Electromagnets are used in countless electric and mechanical devices. They are very important in our daily lives!
Here are some common uses:
- Motors and Generators: They help make things move in motors and create electricity in generators.
- Relays: These are electric switches that use a small current to control a larger current.
- Electric Bells and Buzzers: The ringing sound comes from an electromagnet quickly turning on and off.
- Loudspeakers and Headphones: Electromagnets make the tiny parts vibrate to create sound.
- Data Storage: Devices like hard disks use electromagnets to read and write information.
- Medical Imaging: MRI machines use powerful electromagnets to see inside the human body.
- Particle Accelerators: Huge electromagnets guide tiny particles at very high speeds in scientific experiments.
- Magnetic Locks: These locks use electromagnets to hold doors securely shut.
- Recycling: Large industrial electromagnets are used to pick up and separate magnetic metals (like iron and steel) from other trash.
- Maglev Trains: Some trains use magnetic levitation (maglev) to float above the tracks, allowing them to travel at very high speeds.
How Electromagnets Work
When an electric current flows through a wire, it creates a magnetic field around that wire. To make this field stronger, the wire is wound into a coil with many turns. The magnetic fields from all these turns combine in the center of the coil, making a powerful magnetic field there. A coil shaped like a straight tube is called a solenoid.
You can figure out the direction of the magnetic field using a simple trick called the right-hand rule. Imagine curling the fingers of your right hand around the coil in the direction the electricity is flowing. Your thumb will then point in the direction of the magnetic field inside the coil. This direction is called the north pole of the electromagnet.
To make the magnetic field even stronger, a "magnetic core" is often placed inside the coil. This core is usually made of a soft iron material. This core can increase the magnetic field thousands of times! However, some very strong electromagnets, like those that use superconducting wires, don't use these cores.
Super Strong Electromagnets
Superconducting Electromagnets
When scientists need a magnetic field that is incredibly strong, much stronger than what iron-core electromagnets can produce, they use superconducting electromagnets. These magnets use special wires called superconductors. When these wires are cooled down to extremely cold temperatures, usually with liquid helium, they can carry electricity without any electrical resistance. This means huge amounts of current can flow, creating incredibly intense magnetic fields.
Superconducting magnets are very powerful, but they are also expensive because of the special cooling equipment they need. However, once they are running, they use less power because no energy is lost as heat in the wires. They are used in particle accelerators and MRI machines, which are vital for science and medicine.
Bitter Electromagnets
Even without a core, some electromagnets can be incredibly powerful. The strongest man-made magnetic fields are often created by special "air-core" electromagnets called Bitter electromagnets. These were invented by Francis Bitter in 1933.
Instead of wire windings, a Bitter magnet is made of a stack of conducting disks. Electricity flows through these disks in a spiral path, creating a super strong magnetic field in the center. This design is very strong and can handle the huge forces created by the powerful magnetic field. These disks also have holes for cooling water to pass through, which helps remove the massive amount of heat produced by the high electric current.
The strongest continuous magnetic field ever made by a resistive magnet is 41.5 tesla. Even more powerful fields, up to 100 tesla, have been created for very short bursts of time. This is because the heat produced during these short pulses can be removed before the next pulse.
Images for kids
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Large aluminum bars carrying current into the electromagnets at a high-field laboratory.
See also
In Spanish: Electroimán para niños
