How "Electromagnetic Waves" Transmits Information - Introduction to Communication Technology PPT Courseware 2

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How "Electromagnetic Waves" Transmits Information—Introduction to Communication Technology PPT Courseware 2

Pre-study tips

1. Radio and television use _____ to transmit information.

2. _____ can generate electromagnetic waves in the surrounding space.

3. In radio stations, _____ is used to generate electromagnetic waves

4. Does the propagation of electromagnetic waves require a medium?

5. The propagation speed of electromagnetic waves in vacuum is

6. The relationship between wavelength, wave speed and frequency

knowledge window

Frequency: The number of wave crests (or troughs) that appear within 1 second is called the frequency of the wave

Wave speed as a function of wavelength and frequency.

Wave speed = wavelength × frequency

The propagation speed of electromagnetic waves in vacuum is the same as the speed of light, which is 3×108 meters/second.

Approximately in air and in vacuum.

Discuss?

Turn on the semiconductor radio and tune it to a place where there is no radio station so that the radio cannot receive the radio station's broadcast. Then turn up the volume and place the radio close to a 220-volt AC line. You will hear "noise" from the radio. why is that?

Classroom test:

1. The propagation speed of electromagnetic waves in vacuum is ____ m/s, which is the fastest speed of material movement in the universe. This speed has a special symbol ____. The relationship between the wavelength λ of electromagnetic waves, frequency f and speed c is ____, it can be seen that the higher the frequency of the electromagnetic wave, the _____ its wavelength.

2. The wavelength range of the electromagnetic waves emitted by the first program of Beijing TV Station is 1.7 meters to 1.8 meters, so the frequency range of this electromagnetic wave is ____ Hz to ____ Hz.

3. At present, two sets of satellite TV programs of China Educational Television are forwarded through the domestic "Dongfanghong 2A" communication satellite. The satellite forwarding downlink frequencies are 3848 MHz and 3928 MHz. The wavelengths of these two electromagnetic waves are ____ and ____.

4. Propagation of electromagnetic waves ( )

A. Can only spread in the air B. Can only spread in a vacuum

C. Cannot spread in the air D. Can spread in a vacuum

5. Which of the following household appliances uses electromagnetic waves to work ( )

A. Refrigerator b. Microwave oven c. Soldering iron D. washing machine

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Update Time: 2024-07-26

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