California State University, Bakersfield. Signals and Systems. Luis Medina,

Transcription

1 Luis Medina, Department of Electrical and Computer Engineering, California State University, Bakersfield Lecture 9 (Intro, History and Background) July 29 th,

2 Electric Fields An electric field surrounds an electrically charged particle. The direction of the electric field depends on the charge of the particle. For a positive charge, the electric field is radially outward. For a negative charge, the electric field is radially in toward the charge. 2

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4 A particle placed in the electric field will experience an electric force. Depending on the charge of the particle, it will experience an attractive force or a repelling force. 4

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6 Magnetic Fields A magnetic field is produced when a charged particle is moving. A charged particle can also experience a magnetic force in a magnetic field. As with electric fields, like polarities repel and opposite polarities attract. 6

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8 Hans Christian Oersted discovered that an electric current produced a magnetic field. 8

9 When you have two parallel wires carrying a current, each wire experiences a force from the other. Currents in the same direction attract each other and currents in the opposite direction repel. 9

10 Electromagnetic waves An electromagnetic wave is a combination of a changing electric field wave and changing magnetic field wave. These electric and magnetic field waves are perpendicular to each other and perpendicular to the direction of propagation. 10

11 An electromagnetic wave (EM) is a combination of a changing electric field wave and changing magnetic field wave. These electric and magnetic field waves are perpendicular to each other and perpendicular to the direction of propagation. 11

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13 Light is one example of an electromagnetic wave. EM waves have different frequencies and wavelengths. Light can be split up to different colors each with a different wavelength. 13

14 The visible light only makes up a very small portion of the EM spectrum. EM waves do not require a medium to travel like sound waves, and can travel in vacuum. 14

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17 Applications 17

18 Radio waves Radio waves are used to transmit information. Used by radio stations, television and cell phone companies. 18

19 Microwaves Microwave radiation is used in microwave ovens to heat up your food. Radar guns use microwaves to check the speed of moving cars. Wi-Fi and other forms of wireless communications use microwaves for data transmission. 19

20 Infrared 20

21 Infrared Infrared radiation is emitted by anything with temperature. Infrared sensors can be used to produce images in the dark. Satellites also use infrared sensors to get the surface temperature of Earth. 21

22 Ultraviolet 22

23 Ultraviolet The sun emits ultraviolet light and causes sunburn. Security: ultraviolet light can be used to detect counterfeit money. UV light is also used in sanitizing water, detect bodily fluids and tanning beds. 23

24 X-ray 24

25 X-rays X-ray machines are used in checking for broken bones. X-ray machines are also used in airports to find any hidden weapons. 25

26 Electromagnet A wire carrying a current produces a magnetic field. Wrapping a wire around a ferromagnetic core like iron will become magnetized and act like a magnet. 26

27 Electromagnets can be turned on and off, unlike permanent magnets. Electromagnets are used to easily move heavy metal objects like cars in a junkyard. 27

28 Applications of electromagnets 28

29 Doorbell Doorbells use electromagnets to get the clapper to hit the bell. Once the clapper hits the bell, the circuit is incomplete and no current flows and the electromagnet is not magnetized. 29

30 Loudspeaker A loudspeaker uses a permanent magnet and electromagnet to work. 30

31 Electric motor This electric motor uses a permanent magnet to make the coil spin. When current is flowing in the coil, the coil experiences a force from the magnetic field and causes the coil to spin. 31

32 Important people 32

33 Hans Christian Oersted Discovered a relationship between electricity and magnetism. Oersted s experiments showed that an electric current produced a circular magnetic field. 33

34 Michael Faraday The discoveries made by Faraday, had major influence in the field of electromagnetics. His major discovery was based on a phenomenon that is known as mutual induction. 34

35 Faraday s experiment Faraday s experiment showed the property of mutual induction. When current was applied to one side of the loop, a magnetic field was produced. This then produced a current on the other side of the loop. 35

36 Faraday also worked on the first electric motor. 36

37 James Clerk Maxwell While studying the properties of electricity and magnetism, Maxwell was able to reduce previous experimental observations into 4 equations, known as Maxwell s equations. 37

38 Maxwell s equations 38

39 Maxwell s equations hold in any material, even in vacuum. His equations can be reduced when the quantities in his equations don t depend on time. 39

40 Maxwell was able to calculate the speed of propagation of an electromagnetic wave, which is approximately the speed of light. 40