"Radio, Television and Communications" Electromagnetic Waves and Information Age PPT Courseware

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"Radio, Television and Communications" Electromagnetic Waves and Information Age PPT Courseware

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1. How are electromagnetic waves generated? How to indirectly observe its existence through experiments?

Electromagnetic waves are generated by changing currents. When you turn on a fluorescent lamp, you will hear noise in a nearby radio. This noise is caused by the intermittent current formed when the circuit is on and off, which excites electromagnetic waves in the surrounding space and is received by the radio.

2. What is the propagation speed of electromagnetic waves in vacuum? What is the relationship between wave speed, frequency and wavelength?

3×108m/s, c = λ × f The higher the frequency, the shorter the wavelength

Since electromagnetic waves have different frequencies and wavelengths, their uses are also different. Electromagnetic waves are used for radio, television and mobile communications. With radio and television, the myths of "clairvoyance" and "sound ears" in ancient Chinese legends have become facts.

So how to use electromagnetic waves to transmit sounds and images?

Transmission and reception of radio broadcast signals

Launch: (done by_______)

1. _____ converts _______ into ________

(Audio electrical signals cannot be used directly for transmission) - similar to letters to be sent

2. ____________ produces___________

--Similar to a homing pigeon flying far away

3. ________ loads __________ onto ________

--Similar to tying a letter to a carrier pigeon

4. _____ launch ____________________

--Similar to the release of homing pigeons

Receiving: (done by _____)

1. Antenna: Receive ___________ transmitted in space

(There is no selectivity. If all the electromagnetic waves received by the antenna are turned into sounds, it will only be noisy)

2. Channel selection and modulation:

(1) Select the electromagnetic wave of a certain frequency that we want to receive from various electromagnetic waves through ______

(2) Extract audio electrical signals from high-frequency electrical signals

3. Speaker: Convert audio electrical signals into sound

1. Principles of Radio and Television

(1) Sound and image signals

(2) Convert into electrical signals (audio or video signals)

(3) Convert it into a modulated signal and load it on the high-frequency oscillating current

(4) Emitting electromagnetic waves carrying modulated signals through antennas

(5) Receive the electromagnetic wave carrying the modulated signal and take out the modulated signal, amplify and restore it.

2. Modern Communications

Satellite communications and optical fiber communications, including network communications, can be summed up as modern communications. Their communication process is roughly the same, but they use different channels. One uses satellites in the sky, one uses light sighting underground, and the other uses a network that combines heaven and earth.

1. What is the role of satellites?

2. If people all over the world can see a certain scene immediately, how many satellites are needed as relay stations?

3. Of the many TV programs you watch at home, which ones are delivered via satellite?

1. Radio and television

1. The general process of transmitting sound signals by electromagnetic waves:

Sound signal → audio signal → modulated signal → emit electromagnetic waves → demodulated and restored to sound

2. The general process of electromagnetic waves transmitting TV signals:

Image and sound signals → Video and audio signals → Produce TV programs → Emit electromagnetic waves → Receive and restore images and sounds

2. Satellite communications

Geostationary satellite: The period of rotation of the satellite around the earth is the same as the period of the rotation of the earth.

3. Optical fiber communication

Advantages of fiber optic communication:

1. Strong anti-interference ability. 2. Less signal loss. 3. Large capacity

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Update Time: 2024-08-09

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 2 industry PPT template

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