"Modern Shunfeng Ear─Telephone" Information Transmission PPT Courseware 3

Description

"Modern Shunfeng Ear─Telephone" Information Transmission PPT Courseware 3

conveying information in ancient times

Flying Pigeon Passing Letters

Post stations set up by the government and letters delivered by the private sector

Convey messages with special sounds, such as bells, drums, firecrackers, etc.

Use lights, firelights, such as Kongming lanterns, beacons, etc. to convey information

modern delivery of information

Wired communications: telephone, telegraph, television

Wireless communications: radios, walkie-talkies

Digital communications: Internet, digital TV

Paper communication: letters, newspapers

1. The composition and function of the telephone

Microphone: Converts acoustic signals into electrical signals

Earpiece: Converts electrical signals into acoustic signals

(one),

Microphone structure:

There is a metal box inside the microphone, which is filled with carbon particles and covered with a diaphragm.

effect

When speaking into the microphone, the diaphragm presses the carbon particles tightly and loosely, and their resistance changes accordingly, and the current flowing through the carbon particles changes accordingly, thus forming a current signal that changes with the sound.

Acoustic signal Electrical signal

(two)

Handset structure:

There is a permanent magnet in the earpiece, with solenoids on its two magnetic poles, and a thin iron sheet in front of the magnetic poles.

effect

Inside the earpiece is a magnet with a coil wound around it and a thin iron diaphragm in front of it. Due to the attraction of the magnet, some of the thin iron diaphragm is bent toward the magnetic pole. When the phone is connected, the receiver and the other party's microphone are equivalent to being connected in series. When a current that changes in intensity according to the vibration of the speaking sound is transmitted from the microphone, the magnet The attraction to the diaphragm changes in strength, causing the diaphragm to vibrate and form sound waves in the air, and you can hear the other party speaking.

electrical signal acoustic signal

The principle of telephone

Working principle: The microphone turns the acoustic signal into a changing current. The current transmits the information to the distance along the wire. In another section, the current vibrates the diaphragm of the earpiece, and the current carrying the information becomes sound again.

1. The simplest components of a telephone: microphone, receiver

2. How the old-fashioned telephone works:

1) When speaking into the microphone, the diaphragm presses the carbon particles tightly and loosely, causing the resistance to increase and decrease, thereby causing the current flowing through the carbon particles to increase and decrease. In this way, the microphone converts the acoustic signal into an electrical signal.

2) Through the telephone line, the current passed into the handset flows through the electromagnet. The current is sometimes large and sometimes small, and the attraction of the electromagnet to the diaphragm is also sometimes large and sometimes small, causing the diaphragm to vibrate in different ways and form sound waves in the air. In this way, the earpiece converts the electrical signal into an acoustic signal.

2. The role of telephone exchange

Think about it and draw a picture

(1) How many phone lines are needed?

(2) How can we reduce the number of telephone lines?

telephone exchange

Principle: The fixed phones in an area are all connected to the same exchange in the area. Each phone is assigned a number (i.e. phone number). When connected to the exchange for use, the exchange connects the two telephones that need to be called. After the call is completed, The line is disconnected.

Calls between cities are connected through switches, and users of two different switches can talk to each other.

3. Analog communication and digital communication

1. Analog and digital signals

Telephone signals are divided into two types: analog signals and digital signals.

(1) Analog signal

Take a telephone signal as an example: when the microphone converts sound into signal current, the frequency and amplitude of the current change exactly the same as the frequency and amplitude of the sound.

(2)Digital signal

Take telegraph signals as an example: a combination of dots "·" and "—" is used to represent various numbers, and a certain combination of numbers represents a Chinese character. That is, different combinations of different symbols are used to represent signals.

2. Transmission of analog and digital signals

(1) Analog signal communication can only be used to transmit voice signals (1G signals)

(2) In addition to transmitting voice signals, digital signal communication can also transmit text and pictures (2G signals)

(3) Compare the advantages and disadvantages of the two signal transmissions

Disadvantages of analog communication:

Susceptible to interference, amplification distortion, and formation of noise

Advantages of digital communication:

Small signal distortion, easy storage, easy processing of transmitted data

I'll fill it in

1. The telephone was invented by ______ Chinese _____ in _____.

2. The simplest telephone is composed of ____ and ____. Among them, the one that converts the acoustic signal into an electrical signal is _____, and the one that converts the electrical signal into an acoustic signal is ______. There is a permanent magnet in the _____.

3. One telephone usually communicates with multiple telephones. In order to improve line utilization, people invented ______.

4. The program-controlled telephone exchange has many functions, such as _____, _____, ______.

5. According to the signal transmission method, telephones can be divided into ______ and ______, and the corresponding communication methods are _____ and _____ respectively.

6. __________ is called an analog signal, and ____________________ is called a digital signal. Your phone uses the ________ signal.

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Update Time: 2024-10-03

This template belongs to Physics courseware People's Education Edition Ninth Grade Physics Complete Book industry PPT template

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