# Electromagnetic Induction

## How Generators and Motors Use Electromagnetic Induction

Electromagnetic Induction, according to Merriam-Webster, is "the induction of an electromotive force in a circuit by varying the magnetic flux linked with the circuit." Electric generators use electromagnetic induction through Faraday’s law of induction, which states, “…by spinning a wire coil in a magnetic field at a constant rate can create an oscillating emf.” Generators transform mechanical energy into electrical energy. Motors, on the other hand, transform electrical energy to mechanical energy by passing a current, created by the magnetic force applied by a magnetic field, through a wire coil in a magnetic field, causing the wire coil to spin.

## Electromagnetism In Life

Television

Electromagnetism is used to make televisions display an image. Magnets inside television sets allow them to work and display a picture. A cathode ray tube streams electrons towards the television screen. Without electromagnets, these electrons would travel straight into the television and hit it only in a specific spot. This would not produce a full picture. Strong electromagnets in the cathode ray tube's neck redirect these electrons towards the top, bottom, left, and right sides of the tube and screen. When the electrons strike the screen, an image is produced by a special coating on the inside of the screen that glows when the stream of electrons strikes it.

Computers

Computers use electromagnets to store information and save data to the hard drive. A hard drive saves data by small embedded magnetized pieces of metal. The data begins as computer language, with only digits, such as 0s and 1s. When you save something to the hard drive of the computer, the electrical force running through the computer causes these magnetized pieces to save the information by changing the digits into a pattern that is then embedded in the hard drive. When this information needs to be retrieved, the pattern on the hard drive is converted by the same electrical force and decoded into usable information. This is also why magnets can wipe out the hard drive of computers.

Microphone

A microphone is a sound amplifier which operates as a speaker working in reverse. A microphone makes use of magnet fields, electrical fields, and electromagnets. The most common microphone is the Dynamic Microphone which uses electromagnets. The electromagnets are found in the voice coil. These electromagnets in the microphone are composed of cylinders of iron wrapped around and around in an insulated wire. A permanent magnet surrounds the voice coil. Sound waves from your voice make the diaphragm of the microphone move or vibrate. These vibrations or movements move the permanent magnet, which surrounds the voice coil, to move back and forth on its axis. Since the permanent magnet moves back and forth and creates a magnetic force, the magnetic field in the cylinders of iron changes. The magnetic field change creates an electrical current which flows in the wire wrapped around the magnet. The electrical current varies with the sound and produces an induced current, or audio signal, which can be picked up by a listener or recording equipment.

VCR Tapes

Though considered obsolete, VCR tapes (Video Cassette Recorder) use electromagnetism to store recorded videos and images. Before technology advanced and DVD players were created, a VCR and VCR tapes could be found in almost every home. VCR tapes use electromagnetism to record sound and images. A VCR consists of recording heads, which are electromagnets, and a tape that has a thin layer of iron oxide on the surface. The recording heads on the tape attract particles of metal onto the tape in patterns which the television signals produce. As the signals create this pattern and change in direction and strength, the magnetic field also changes. The tape is pulled past the recording heads. Different positions along the tape are magnetized following different directions and strengths that the pattern produces. The heads of the tape record the electrical signals and store the recorded video and images.

Telephone

A telephone, a common used item, uses electromagnetism to function. The use of electromagnetism is primarily in the earpiece of the telephone. A telephone conversation involves converting the sound waves made by the person speaking into varying electric currents. The varying currents travel along the telephone tower's wire to the other person's receiver. The electromagnet and the permanent magnet in the telephone's earpiece receive these varying currents. They both are attached to a disk. The variation of the currents makes the electromagnet vary in magnet strength. The inconstant magnetic force produced by the electromagnet attracts the permanent magnet and causes the disk to vibrate. This vibration causes sound waves to be produced that closely resemble the original sound waves. The person's voice is then heard on the other end and can continue the conversation, which causes the process to repeat.

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