Electromagnetic Waves - Hong Kong Polytechnic eewlchan/EE1D01/EE1D01_2b.pdfآ  2014. 9. 24.آ ...

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Transcript of Electromagnetic Waves - Hong Kong Polytechnic eewlchan/EE1D01/EE1D01_2b.pdfآ  2014. 9. 24.آ ...

  • EE1D01 Electrical Science for Everyone

    1

    Electromagnetic Waves

    Electromagnetic waves are transverse waves that have some electrical and magnetic properties. They do not need a medium, matter, to travel through. Electromagnetic waves transfer energy by means of changing electric and magnetic fields.

    EE1D01 Electrical Science for Everyone

    2

    Speed of Light

    c = f λ Wavelength (m)

    Frequency (Hz)

    Speed of light 3 x 108 m/sec

  • EE1D01 Electrical Science for Everyone

    3

    Electromagnetic Spectrum

    The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

    EE1D01 Electrical Science for Everyone

    4

  • EE1D01 Electrical Science for Everyone

    5

    Radio Waves Longest wavelength EM waves Applications:

    TV broadcasting AM and FM broadcast radio Wireless control Heart rate monitors Cordless phone communication

    EE1D01 Electrical Science for Everyone

    6

    Microwaves Wavelengths from 1 mm - 1 m Applications:

    Microwave ovens Bluetooth headsets Wi-Fi Radar GPS

  • EE1D01 Electrical Science for Everyone

    7

    Infrared Radiation

    Wavelengths in between microwaves and visible light Applications:

    Night vision goggles Remote controls Thermographs

    EE1D01 Electrical Science for Everyone

    8

    IR Emission from a Cold-blooded Lizard

    Optical Image Far-Infrared Image

    “Room Temperature”

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    9

    Electrical Work

    One of the conductor terminals is hot. Hot Terminal Temperature…..203F Left Terminal Temperature….156F Temperature difference is …… 47F

    癋119.7

    癋179.5

    120

    140

    160

    AR01

    SP01

    EE1D01 Electrical Science for Everyone

    10

    Visible spectrum

    Visible Spectrum

    Prism

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    Red Orange Yellow Green Blue Indigo Violet

    Colour Spectrum

    lowest frequency

    highest frequency

    EE1D01 Electrical Science for Everyone

    12

    Eye Sensitivity to Colour

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    13

    Ultraviolet

    Shorter wavelengths than visible light Applications:

    Sterilizing medical equipment Water disinfection Security images on money

    EE1D01 Electrical Science for Everyone

    14

    X-rays

    Tiny wavelength, high energy waves Applications:

    Medical imaging Airport security Inspecting industrial welds

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    15

    Illumination Level

    Summer shade 10000-15000

    Full moon: 0.5

    Cloudy 25000

    Sunny 50000-100000

    Lux

    Office 400-500

    Workshop 300-1000

    Warehouse 125-300

    Studio 2000

    Shop 500-1000

    Flat 200

    Street 20-70

    20 lux 2000 lux Artificial light

    Natural light

    > Technical Appendix

    EE1D01 Electrical Science for Everyone

    16

    Commonly used Lighting Sources

  • EE1D01 Electrical Science for Everyone

    17

    Incandescent Lamp

    EE1D01 Electrical Science for Everyone

    18

    Colour Temperature

    Object

    You Heat Lamp Candle Flame Bulb Filament Sun’s Surface

    Temperature

    ~ 30 C ≈ 300 K ~ 500 C ≈ 770 K

    ~ 1700 C ≈ 2000 K ~ 2500 C ≈ 2800 K ~ 5500 C ≈ 5800 K

    Colour

    Infrared (invisible) Dull red Dim orange Yellow Brilliant white

    The hotter it gets, the “bluer” the emitted light The hotter it gets, the more intense the radiation

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    Colour Temperature This is a measurement of "warmth" or "coolness" provided by the lamp. People usually prefer a warmer source in lower illuminance areas, such as dining areas and living rooms, and a cooler source in higher illuminance areas, such as grocery stores. Colour temperature refers to the colour of a blackbody radiator at a given absolute temperature, expressed in Kelvin. A blackbody radiator changes colour as its temperature increases ( first to red, then to orange, yellow, and finally bluish white at the highest temperature. A "warm" colour light source actually has a lower colour temperature. For example, a cool-white fluorescent lamp appears bluish in colour with a colour temperature of around 4100 K. A warmer fluorescent lamp appears more yellowish with a colour temperature around 3000 K.

    EE1D01 Electrical Science for Everyone

    20

    Problems with Thermal Light

    Temperature too low, too red Incandescent light bulb, 2500°C The sun, 5800°C

    Not energy efficient Lots of invisible infrared light Only a small fraction of thermal power is visible

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    21

    Incandescent Lamp 1879 (Thomas Edison) Lamp power: 15 to 1000 W Light Output: up to 15,000 lumens Class G to E: Europe has decided to remove these lights from the EU market before 2012

    E27 (ES) E14(SES)B22 (BC)

    S14S15 S19

    Efficiency: Lifetime: Output (lm): Colour: On/off : Frequent Control: Direct

    Advantages

    Bright point light source (if transparent glass)

    Disadvantages

    Energy-guzzler – very low efficiency (E, F or G-class)

    Full compatibility with existing luminaries Risks due to high operating temperature

    Full dimmable on any dimmer

    Good quality and performance

    Short lifetime (1000 hours)

    EE1D01 Electrical Science for Everyone

    22

    Photon Absorption and Emission

  • EE1D01 Electrical Science for Everyone

    23

    Emission Colours of Various Gases

    EE1D01 Electrical Science for Everyone

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    The fluorescent lamp produces light by the passage of an electric current flowing through a vapor of mercury.

    1.Electron emitted from electrode collides with mercury atom. 2.Impact produces ultraviolet rays 3.Phosphor converts ultraviolet to visible light.

    This process is known as “fluorescence,” hence the name fluorescent lamp.

    Fluorescent Lamp

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    25

    Fluorescent Light

    Bulb Wall

    Phosphor

    UV

    Mercury

    Electricity

    Visible Light

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    26

    Phosphors

    A mercury lamp emits mostly invisible UV light To convert its UV light to visible, use a phosphor Phosphors absorb photons and reemit new photons New photon energy is less than old photon energy Fluorescent lamps → phosphors emit white light

    (De luxe) warm white, (de luxe) cool white phosphors

    Specialty lamps → phosphors emit colored light Blue, green, yellow, orange, red, violet, etc.

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    27

    Fluorescent Tubes

    The most frequently used! Accept frequent On/Off switching Lamp power: 4 to 140 W, light output up to 14000 Lumens Lifetime of fluorescent tubes depends on daily On / Off frequency and type of ballast Several types of fixtures according to use: 3m to 12m height (high efficiency), hanging, surface or flush mounted, single, twin or multiple tube fixture, IP 65 version...

    > Overview of building lighting

    T12 (40-65lm/W)

    T8 (80-95 lm/W)

    T5 (95-105 lm/W)

    38mm 26mm 16mm

    Lighting/consumption: Lifetime: Output: Colour:

    On/off: Frequent Control: Ballast Dimmable: Yes

    EE1D01 Electrical Science for Everyone

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    THE BULB •Most fluorescent lamps are made in straight tubular bulbs in various diameters.

    •Circline lamps are in the form of a circle.

    •U-Bent lamps are essentially straight lamps bent to form a U shape.

    Elements of a Fluorescent Lamp

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    29

    Elements of a Fluorescent Lamp

    THE ELECTRODES •Coiled tungsten wires coated with an emission material •When heated, emit electrons •Electrons bombard mercury atoms producing ultraviolet rays.

    THE PHOSHPORS Phosphors are the coated powders on the inside of the bulb that convert the

    ultraviolet rays to visible light. There are two basic types: • Halophosphates • Trichromatics or Triband Phosphors

    EE1D01 Electrical Science for Everyone

    30

    Ballasts All fluorescent lamps require a ballast for starting and operation. The ballast has two basic functions: •Limit the lamp’s operating current •Provide the required voltage to start the lamp LIMITING THE CURRENT •When a fluorescent lamp is started, its resistance to the current flow decreases dramatically. •If not controlled, the current would increase rapidly and destroy the lamp virtually instantaneously. •The ballast limits the current.

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    Fluorescent lamp that is small in size (~2 in. diameter, 3 to 5 in. in length). Developed as replacement for incandescent lamps. Two Main Types

    Ballast-integrated. Ballast non-integrated (allows only lamp to be replaced).

    Compact Fluorescent Lamps (CFLs)