Ch. 4 Ch. 4 Application of Electromagnetic WavesApplication of Electromagnetic Waves

Electromagnetic Spectrum (電磁波譜 )

highest frequencylowest frequency

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Electromagnetic spectrum:1. Radio Waves (無線電波 )2. Microwaves ( 微波 )3. Infra-red rays ( 紅外線 )4. Visible Light ( 可見光 )5. Ultra-violet rays ( 紫外線 )6. X-rays (X 光 )7. Gamma rays ( 伽瑪射線 )

Note: We can see the visible light only.

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Applications (應用 ) of Electromagnetic Waves (電磁波 )

4.1 Radio Waves (無線電波 )

(a) Radio (電台 ) and Television (電視 ) broadcast (廣播 )

Radio Waves Antenna(receiving signals)

Aerial (transmitting signals)original

sound

reproducedsound

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(b) Wireless telecommunication (無線通訊 ) in mobile phone (手提電話 ) wireless computer network (無線電腦網絡 ) Bluetooth (藍芽 ) headset Walkie talkie (對講機 )

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4.2 Microwaves ( 微波 )

(a) Satellite Communication (衛星通訊 )

satellite

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(b) Radar (雷達 )

microwaves

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Class Exercise 4.1The US F-117 fighters are designed to be invisible to radar. Suggest some of its features (特徵 ).

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Class Exercise 4.1The US F-117 fighters are designed to be invisible to radar. Suggest some of its features (特徵 ).

1. Surface layer can absorb microwaves.

2. Large flat areas on the top and bottom of the aircraft reflect most of the incoming microwaves.

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(c) Microwave Oven (微波爐 )

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4.3 Infra-red Radiation (紅外輻射 )

(a) Remote Control (遙控 )

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(b) Infrared Thermometer (溫度計 )

(c) Thermography (熱力圖 )

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(d) Infrared Camera (紅外線相機 )

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(e) Infrared Sensors (紅外線感應器 )

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(e) Infrared Sensors (紅外線感應器 )

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4.4 Ultra-violet rays (紫外線 )

(a) Checking of banknotes (核對鈔票 )

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(b) Sterilisation (消毒 )

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(c) Making of vitamin D (維生素 D)

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Class Exercise 4.2

Suggest some methods to prevent over exposure (暴露 ) to UV radiations?

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Class Exercise 4.2Suggest some methods to prevent over exposure (暴露 ) to UV radiations?

1. Use Suntan lotion (防曬油 )2. Wear Hat3. Wear Anti-UV cloth4. Wear Sunglasses5. Use Umbrella 6. …

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4.5 X-rays (X 光 )

(a) medical diagnosis (醫學診斷 )

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4.5 X-rays (X 光 )

(b) inspect luggage (檢查行李 )

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4.6 Gamma rays (伽瑪射線 )

(a) Radiotherapy (放射治療 )： killing cancer cells (殺癌細胞 )

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(b) Sterilisation (消毒 ) of medical equipment.

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Homework: Assignment Book 1. Chapter 3 Q.1 – Q.3 (p.4)

Chapter 4 Q.1 – Q.4 (p. 5-6)

2. Deadline: 6-10-2010 (Wed)