ECE170 the basis of electric power generation. Examples


ECE170. ASSIGNMETN 1 2 INTRODUCTIOM Electromagnetism is the science of charge and of the forces and fields associated with charge. Electricity and magnetism are two aspects of electromagnetism. Electric forces are produced by electric charges either at rest or in motion. Magnetic forces, on the other hand, are produced only by moving charges and act solely on charges in motion. A changing magnetic field produces an electric field, as the English physicist Michael Faraday discovered in work that forms the basis of electric power generation. Examples of electromagnetic waves traveling through space independent of matter are radio and television waves, microwaves, infrared rays, visible light, ultraviolet light, X-rays, and gamma rays. All of these waves travel at the same speed—namely, the velocity of light (roughly 300,000 kilometers, or 186,000 miles, per second). They differ from each other only in the frequency at which their electric and magnetic fields oscillate. i Everyday modern life is pervaded by electromagnetic phenomena. Radio and television sets receive information carried by electromagnetic waves traveling through space at the speed of light. In this report, nine applications of devices working on electromagnetic principles will be listed.

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ECE170. ASSIGNMETN 1 3 1. THE ELECTRIC MOTOR An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy by induction. The motor contains an electromagnet that is connected to a shaft. When current flows through the motor, the electromagnet rotates, causing the shaft to rotate as well. The rotating shaft moves other parts of the device. When current flows through the electromagnet, it becomes magnetized, and its poles are repelled by the like poles of the permanent magnets. This causes the electromagnet to rotate toward the unlike poles of the permanent magnets. A device called a commutator then changes the direction of the current so the poles of the electromagnet are reversed. The reversed poles are again repelled by the poles of the permanent magnets, which have not reversed. This causes the electromagnet to continue to rotate.ii

ECE170. ASSIGNMETN 1 4 2. MAGLAV TRAINS A maglev (magnetic levitation) train works without wheels and is propelled by electromagnetic forces. It consists of a set of magnets along the bottom of the train and a series of electromagnets on the tracks or guide-way for the train. The electromagnets are adjusted to have the same polarity as the train’s magnets, though complex computer controls. Since the magnetic poles repel, the train is levitated or floats slightly above the track. Guides on the sides prevent the train from sliding off. Depending on the position of the train, the polarity of the electromagnets is adjusted, causing the train to move forward. Maglev trains can reach speeds over 260 mile per hour or 430 kilometers per hour.

ECE170. ASSIGNMETN 1 5 3. ELECTROMAGNETIC CRANES Electromagnetic lifting cranes are used to lift and transport steel scraps, sheets, medium and thick plates, and steel bars. They use electromagnetism to magnetize the coil for lifting and demagnetize the electromagnetic coil for dropping the materials in the required place. The magnetic strength of an electromagnet depends on the number of turns or wire and the current through the wire, and the size of the iron core. This allows electromagnets to be made much larger and stronger than a natural magnet, such that they can pick up very large objects. Also, when you turn off the electricity to an electromagnet, the magnetism is also turned off. Thus, an electromagnet can be used to pick up a piece of iron and then drop it someplace else.iii

ECE170. ASSIGNMETN 1 6 4. SPEAKERS Speakers come in all shapes and sizes, enabling you to listen to music on your iPod, enjoy a film at the cinema or hear a friend’s voice over the phone. A speaker is used to translate an electrical signal into an audible sound, it consists of an electromagnet: a metal coil, which creates a magnetic field when a current flows through it. This coil behaves much like a normal (permanent) magnet, with one particularly handy property: reversing the direction of the current in the coil flips the poles of the magnet. Inside a speaker, an electromagnet is placed in front of a permanent magnet. The permanent magnet is fixed firmly into position whereas the electromagnet is mobile. As pulses of electricity pass through the coil of the electromagnet, the direction of its magnetic field is rapidly changed. This means that it is in turn attracted to and repelled from the permanent magnet, vibrating back and forth. The electromagnet is attached to a cone made of a flexible material such as paper or plastic which amplifies these vibrations, pumping sound waves into the surrounding air and towards your ears.iv 5. ELECTRIC FANS Electric fans, blowers and other cooling systems use electric motors. These motors work on the principle of electromagnetic induction, which is the branch of electromagnetism. In any electrical appliance, electric motor is moved by the magnetic field produced by the electric current according to the Lorenz force principle. These motors are vary in size, rating and cost based on the application.v

ECE170. ASSIGNMETN 1 7 6. MICROWAVE Microwave ovens work by producing electromagnetic waves. The waves are called microwaves and are of course what give microwave ovens their name. Different types of waves behave differently because they come in different lengths. Microwave wavelengths fall between those of the tiny infrared waves used in conventional ovens and the much longer FM radio waves, which broadcast your favorite music to your car stereo. The conventional oven uses a gas flame or electric elements to produce infrared waves which heats both the food and the air around the food. The microwave oven uses a device called a magnetron to produce microwaves, which are directed to the inside of the microwave oven via a tube called a wave guide. The microwaves bounce around inside the microwave oven until they hit water, sugar or fat molecules in the food. Every 2.45 billionths of a second, the magnetron tube emits a microwave. Each microwave alternates between a positive and negative charge. This rapid switching causes the water, sugar or fat molecules in the food to repeatedly spin around to the opposite polarity a bit like how the needle of a compass would flick from north to south if you kept passing a magnet back and forth across the face of the compass. vi

ECE170. ASSIGNMETN 1 8 6. WIRELESS POWER TRANSFER Wireless power transmission refers to a power source that sup- plies a system with energy without the hassle of interconnecting wires. Wireless power transmission problems differ from those of wireless telecommunications, such as radio. While in wireless power efficiency is considered to be the more significant cant parameter, in wireless telecommunications the proportion of energy received becomes critical only if it is too low for the signal to be distinguished from the background noise. Electromagnetic induction. When magnetic flux owing through a coil changes, an electromotive force (emf) is induced in the coil along with current. The famous Faraday’s law (which relates to the induced emf in any closed loop including a closed circuit) is the central principle behind electromagnetic induction. Induction can be also be used as a means of wireless power transfer. A changing current in one coil induces emf in another coil. The coils are not in contact and in this way energy can be very simply transported over short distances. The largest drawback of this method is that the short distance required for induction limits its application to very close-range situations.vii

ECE170. ASSIGNMETN 1 9 7. MAGNETIC RESONANCE IMAGING (MRI) Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to visualize internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. MRI machines make use of the fact that body tissue contains lots of water, and hence protons (1H nuclei), which get aligned in a large magnetic field. Each water molecule has two hydrogen nuclei or protons. When a person is inside the powerful magnetic field of the scanner, the average magnetic moment of many protons becomes aligned with the direction of the field. A radio frequency current is briefly turned on, producing a varying electromagnetic field. This electromagnetic field has just the right frequency, known as the resonance frequency, to be absorbed and flip the spin of the protons in the magnetic field. After the electromagnetic field is turned off, the spins of the protons return to thermodynamic equilibrium and the bulk magnetization becomes re-aligned with the static magnetic field. During this relaxation, a radio frequency signal (electromagnetic radiation in the RF range) is generated, which can be measured with receiver coils.viii

ECE170. ASSIGNMETN 1 10 8. HARD DRIVES Hard drives store government files, weather reports, your emails, the pictures on your digital camera, and many other things. In fact, hard drives are the backbone of the Internet: almost everything you see online is being stored on a hard drive. Hard drives use magnetic recording to store information: much like a cassette tape. Hard drives store data using electromagnets. The hard drive consists of the platter and the actuator. The platter is a hard material that is ferromagnetic (able to be magnetized). This is where your files are stored. The actuator arm, the piece that writes the data, magnetizes certain parts of the platter, giving it a value of 0 or 1. To read the data, the arm goes back over the data and interprets these magnetized areas. The other parts of the hard drive simply allow this recording and reading process to happen. The IDE connector and jumper block connect the drive to the rest of the computer, allowing the computer’s operating system to interact with the drive. The power connector supplies the electromagnet and other moving parts with electricity, allowing them to work. The actuator arm writes the data, but it is controlled by the actuator and moves on the actuator axis. Finally, the spindle allows the platter to spin while data is being read from and written to it.ix

ECE170. ASSIGNMETN 1 11 9. X-RAYS X-rays are a form of electromagnetic radiation, as are radio waves, infrared radiation, visible light, ultraviolet radiation and microwaves. One of the most common and beneficial uses of X-rays is for medical imaging. X-rays are also used in treating cancer and in exploring the cosmos. Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum. The EM spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are: radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays. x

ECE170. ASSIGNMETN 1 12 REFRENCES i ii iii iv v Https:// vi vii. viii ix x

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