In its simplest form, an electromagnet consists of a coil of wire carrying an electric current. The strength of its magnetic field depends on the number of turns in the coil and the amount of current passing through it. If you put an iron core inside the coil, the magnetic field strengthens significantly.
Scientists use a machine called a cyclotron to investigate the behaviour of atoms and subatomic particles. In the cyclotron, electromagnets accelerate particles to velocities close to the speed of light. When particles collide with each other at these speeds, they throw off tiny, short-lived fragments, revealing the inner make-up of the original objects. Cyclotrons use some of the world's most powerful electromagnets.
Hospitals and clinics use magnetic resonance imaging machines to create 3-D pictures of the human body. A powerful electromagnet is an essential part of the machine. The MRI's magnet is about 10,000 times stronger than a refrigerator magnet. It sits in a bath of liquid helium that chills it to --233 degrees Celsius. The machine uses the magnet to produce radio waves from the atoms in your body. A computer detects the radio waves and turns them into a detailed picture.
Some cars have shock absorbers that adjust automatically to changing road conditions. The shock absorbers have a special magnetic fluid surrounded by an electromagnet coil. As electric current flows through the coil, the fluid becomes thicker, dampening the motion of the car. The fluid responds in a fraction of a second, so the car's suspension reacts quickly to rapid manoeuvres, potholes and rough surfaces.
In 2011, researchers began work on developing weapons that use electromagnets. These weapons, called coilguns and railguns, use magnetic fields to accelerate metal projectiles to speeds as high as Mach 8, or 1.7 miles per second. The impact energy of the projectile alone causes damage. The device needs no chemical propellants or explosives, just large electrical currents.