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Electricity and Magnetism

Electricity and Magnetism. Dr. Tamer Abdallah. 2009. What is Magnet?.

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Electricity and Magnetism

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  1. Electricity and Magnetism Dr. Tamer Abdallah 2009

  2. What is Magnet? A magnet is any piece of iron, steel or magnetite that has the property of attracting iron or steel. Magnetite also known as lodestone, is a naturally occuring rock. This natural magnet was first discovered in a region known as magnesia and was named after the area in which it was discovered.

  3. Magnet shapes Bar Horseshoe Earth

  4. In 1831 in England Michal Faraday do an amazing experiment Showed that emf can be Induced in a circuit by Changing magnetic field. Also in the same year Joseph Henry in USA do The same experiment independently

  5. These results are quite remarkable in view of the fact that a current is set up even though no batteries are present in the circuit! We call such a current an induced current and say that it is produced by an induced emf.

  6. something quite amazing happens when the switch in the primary circuit is either opened or thrown closed. At the instant the switch is closed, the galvanometer needle deflects in one direction and then returns to zero. At the instant the switch is opened, the needle deflects in the opposite direction and again returns to zero.

  7. In each case, an emf is induced in the circuit when the magnetic flux through the circuit changes with time. B = BA Cos 

  8. Example 1.1 A coil consists of 200 turns of wire. Each turn is a square of side 18 cm, and a uniform magnetic field directed perpendicular to the plane of the coil is turned on. If the field changes linearly from 0 to 0.50 T in 0.80 s, what is the magnitude of the induced emf in the coil while the field is changing? Solution Since  = zero  cos 0 = 1 4.05 volts

  9. Example 1.2 Consider a single circular loop (or coil) with a 2.50-cm radius in a constant magnetic field of 0.625 T. Find the magnetic flux through this loop when it’s normal makes an angle of (a) 0o, (b) 30.0o, (c) 60.0o, and (d) 90.0o with the direction of the magnetic field B. Solution

  10. Example 1.3 The induced emf in a single loop of wire has a magnitude of 1.48 V when the magnetic flux is changed from 0.850 T.m2 to 0.110T.m2. How much time is required for this change in flux? Solution Using equation 1.3

  11. Ground Fault Interrupter GFI

  12. Electric Guitar

  13. Magnetic Tape Recording

  14. Lenz’s Law The induced current in a loop is in the direction that creates a magnetic field that opposes the change in magnetic flux through the area enclosed by the loop.

  15. Alternating current (AC) generator

  16. Alternating current (AC) generator

  17. Direct (DC) generator

  18. Direct (DC) generator

  19. Direct (DC) generator

  20. Motors Motors are devices into which energy is transferred by electrical transmission while energy is transferred out by work. Essentially, a motor is a generator operating in reverse. Instead of generating a current by rotating a coil, a current is supplied to the coil by a battery

  21. Eddy currents

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