"End of Chapter Review" Information Transmission PPT

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"End of Chapter Review" Information Transmission PPT

Part One: Knowledge Versatility

1 A kind of wave: electromagnetic wave

(1) Generation of electromagnetic waves: When there is a rapidly changing current in a circuit, electromagnetic waves can be generated around it.

(2) Propagation of electromagnetic waves: no medium is required and can also propagate in a vacuum. The wave speed of electromagnetic waves in vacuum is c≈3×108 m/s. (3) Characteristics of electromagnetic waves ① All waves have three physical quantities: wave speed, wavelength and frequency.

a. Wavelength: The distance between two adjacent wave peaks (or wave troughs) is the wavelength, represented by "λ", as shown in Figure 21-Z-1. In the SI unit, the unit of wavelength is m.

b. Frequency: The number of wave peaks (or the number of wave troughs) that appear within 1 s at a certain location, represented by "f", and the unit is Hz.

c. Wave speed: the distance a wave travels in 1 s. The speed of electromagnetic waves in vacuum is represented by "c", and the unit is m/s.

②The relationship between wave speed, wavelength and frequency is v=λf or c=λf.

2 Two ways: analog communication and digital communication

(1) Analog communication: When the microphone converts sound into signal current, the frequency and amplitude of the signal current change exactly the same as the frequency and amplitude of the sound, "imitating" the "every move" of the sound signal. The signal transmitted by a current is called an analog signal, and the communication method using analog signals is called analog communication.

(2) Digital communication: Use "·" and "—", "0" and "1" as well as the length of sound, the length of light, the presence or absence of current, etc. to form various combinations to transmit colorful sounds and images. and other information. Signals represented by different combinations of different symbols are called digital signals, and the communication method using digital signals is called digital communication.

3 Four types of communication

(1)Microwave communication

① Advantages: high frequency and large capacity for transmitting information.

② Disadvantages: When encountering mountains, seas, etc., and it is impossible to build relay stations, microwave communication cannot continue.

(2) Satellite communication

① Advantages: long communication distance, wide area, large communication capacity, high reliability, good flexibility and low cost.

②Disadvantages: “high, poor, slow”. High: The communication tariff standard is higher than that of commonly used cable communication; Poor: In large buildings or mountains

When the device itself is covered by objects such as objects, the communication signal is absent or flickers erratically; Slow: There is a delay during the call, resulting in poor communication.

(3) Optical fiber communication

① Advantages: The transmission frequency band is extremely wide and the communication capacity is large; because the optical fiber attenuation is small and there is no relay equipment, the transmission distance is long; the optical fiber is resistant to electromagnetic interference and has good confidentiality; the optical fiber is small in size and light in weight, and is easy to transport and lay; optical fiber It is made of quartz glass, with rich sources of raw materials, saving a lot of non-ferrous metals.

②Disadvantages: The bending radius of the optical fiber should not be too small; the cutting and connecting operations of the optical fiber are technically complex; splitting and coupling are troublesome.

(4) Network communication

① Advantages: The widest coverage, the largest scale, and the richest information resources. Resource sharing, information transmission is fast.

② Disadvantages: It is vulnerable to hacker attacks, causing losses to units and individuals, and harmful information can spread quickly.

Review PPT at the end of the chapter, part 2 content: Practical high school entrance examination

Test Point 1: Generation and Propagation of Electromagnetic Waves

(1) Generation of electromagnetic waves: When the current in a conductor changes rapidly, electromagnetic waves will be generated around it. (2) Propagation of electromagnetic waves: The propagation of electromagnetic waves does not require a medium and can also propagate in a vacuum. The wave speed of electromagnetic waves in vacuum is c≈3×108 m/s. The wave speed, wavelength and frequency of electromagnetic waves satisfy the relationship v =λf; electromagnetic waves of different frequencies propagate at the same speed in vacuum. (3) Radio waves: The part of electromagnetic waves used in radio, television and mobile phones with frequencies from hundreds of kilohertz to hundreds of megahertz is called radio waves.

Example 1 [Nanjing High School Entrance Examination] The following understanding of electromagnetic waves is correct ()

A. Refrigerators work using electromagnetic waves

B． Visible light is not an electromagnetic wave

C. Electromagnetic waves can be used to transmit information

D． The propagation speed of electromagnetic waves in vacuum is 3.0×105 m/s

Test Point 2 Radio, Television and Mobile Communications

(1) The transmission of radio broadcast signals is completed by the radio station. The microphone converts the announcer's voice signal into an electrical signal, and then uses a modulator to load the audio electrical signal onto a high-frequency current, and then generates electromagnetic waves through the antenna and transmits them out; the signal The reception is done by the radio, the tuner selects the signal of a specific frequency, the demodulator detects the audio signal, and finally the speaker converts the audio signal into sound.

(2) Television uses electromagnetic waves to transmit image signals and sound signals.

(3) Mobile phones are both radio transmitters and radio receivers and need to be transferred by a base station.

Example 2 [ Dalian High School Entrance Examination ” or “superconductor”) material.

Answer Electromagnetic Semiconductor

Example 3 [Mianyang High School Entrance Examination] The tall TV towers in various places are landmark buildings. The function of the antenna on the TV tower is ()

A. Convert sound and image signals into electrical signals

B． Let sound and image signals be loaded onto high-frequency current

C. Let audio and video electrical signals be loaded onto high-frequency current

D． Let high-frequency current carrying audio and video signals generate electromagnetic waves

Test point 3: Transmission of information

Modern information dissemination methods include microwave communication, optical fiber communication, satellite communication, and network communication.

(1) Information theory shows that the higher the frequency of the electromagnetic wave used as a carrier, the more information can be transmitted in the same time. Microwave communication uses microwaves as a carrier because of its higher frequency and larger capacity; however, microwaves generally propagate in straight lines and cannot be diffracted along the earth's surface. Therefore, microwave relay stations must be built to transmit microwave signals over long distances.

(2) The satellite communication system consists of communication satellites, ground stations and transmission systems. The communication satellite is an unmanned aerial microwave relay station. It receives the electrical signal transmitted from one ground station, amplifies it and then sends it back to another station after amplification and frequency conversion. One or several ground stations. Global communications can basically be achieved with three communication satellites. Many of the television programs we see now are transmitted via satellite.

(3) Laser is a kind of light with very pure color and highly concentrated direction. Its intensity exceeds that of sunlight. In order to avoid interference and reduce energy loss, lasers used for communication must propagate in optical fibers.

(4) The English name of the Internet is the Internet, also known as the Internet. It uses communication lines and electromagnetic waves to connect computer networks distributed around the world to transmit signals. Through computers, you can step into the information highway of the Internet and get all kinds of information from all over the world without leaving home.

Example 4 　[Chengdu High School Entrance Examination] Regarding electromagnetic waves and information technology, which of the following statements is correct ()

A. Electromagnetic waves can only be used for communication

B． The application of electromagnetic waves is beneficial and harmless to human beings

C. Mobile phones can both emit and receive electromagnetic waves

D． Satellite communications do not require the use of electromagnetic waves to transmit information

Example 5 [Fuxin High School Entrance Examination] With the advent of the digital age, we can already easily use Wi-Fi, 3G or 4G networks for wireless mobile Internet access. Among the following statements about mobile Internet access, which one is correct ()

A. Using infrared rays to transmit digital signals B. Using ultrasound to transmit digital signals

C. Using optical fiber to transmit digital signals D. Transmitting digital signals using electromagnetic waves

Review the PPT at the end of the chapter, the third part: Entering the majors and high schools

Advantage 1: Electromagnetic waves

Mastering physics knowledge and being able to flexibly apply physics knowledge to solve problems is not only a basic requirement for physics learning, but also a basic content of physics exams. It is also an important way to cultivate innovative abilities. After learning about the characteristics of electromagnetic waves, mobile phones and microwave communications, you can design some practical circuits as needed. This is a common question type in physics exams. The purpose is to test the ability to apply knowledge, scientific inquiry and practical innovation.

Typical Example 1 (Experimental Design Question) [Beijing High School Entrance Examination] We live in a sea of ​​electromagnetic waves. When it is necessary to prevent electromagnetic wave interference, metal shells are usually used to separate the electromagnetic waves from the areas that need to be shielded to avoid electromagnetic waves. Enter, this approach is electromagnetic shielding. There is a metal cabin in the China Science and Technology Museum. The large window on the side is inlaid with a piece of electromagnetic shielding glass, as shown in Figure 21-Z-2. Please design an experiment with your own equipment to test whether this piece of electromagnetic shielding glass can shield electromagnetic waves. Write down the experimental procedures and judgment methods.

Solution: (1) Experimental equipment: two mobile phones that can work normally.

(2) Experimental method: Place a mobile phone in a metal cabin, use another mobile phone to dial the number of this mobile phone, listen to whether the mobile phone rings, and see whether the mobile phone receives an incoming call signal.

(3) Judgment method: If the mobile phone in the metal cabin cannot receive a signal, it means that the electromagnetic shielding glass has a shielding effect; if the mobile phone receives a signal, it means that the electromagnetic shielding glass has no shielding effect.

Typical example 2 (material expansion question) Microwave is a very "personalized" electromagnetic wave: microwaves are reflected as soon as they hit metal, and metal cannot absorb or conduct them at all; microwaves can pass through insulating materials such as glass, ceramics, and plastics. But it does not consume energy; when microwaves touch food containing moisture, most of its energy is absorbed by the food. Excessive microwave radiation is harmful to the human body. The casing of a microwave oven is made of metal materials such as stainless steel, and the food container is made of insulating materials. The magnetron in the microwave oven can generate microwaves with a vibration frequency of 2.45×109 Hz, which can reach a depth of 5 cm inside the food, causing the water molecules in the food to vibrate. The violent vibration generates a large amount of heat, which is absorbed by the food, so the food "cooks" "It's cooked. The cooking speed in a microwave oven is 4 to 10 times faster than other stoves, and the thermal efficiency is as high as over 80%.

(1) The microwaves generated in the microwave oven belong to ()

A. Infrasound B. Electromagnetic waves C. Ultrasound D. infrared

(2) When a household uses a microwave oven to work, the energy conversion process is ______ energy into ______ energy.

(3) When the microwave oven is in use, food cannot be placed in metal containers and then placed in the oven for heating. Please briefly describe the reason based on the content of the short article.

(4) Compared with other stoves, what are the main reasons why microwave ovens cook quickly and have high thermal efficiency?

Solution: (3) Metal materials only reflect microwaves but do not absorb them, so food cannot obtain energy.

(4) ① Microwaves consume almost no energy on metal shells and food containers; ② Microwaves can reach 5 cm deep into the food, heating both the inside and outside of the food at the same time, and most of its energy is absorbed by the food.

Training Advantage 2: Information Road

Reading science and technology articles, finding useful information and solving related problems by combining the learned physics knowledge is a more common high school entrance examination question in recent years. It mainly tests reading ability, information processing ability and application ability of physics knowledge. It also helps To improve independent learning ability.

Typical example 3 (material expansion question) Read the following passage and answer the questions.

Explore the world’s largest “sky-gazing eye”

The world's largest single-aperture spherical radio telescope project (FAST in English) built in Guizhou Province is vividly called China's "giant sky-gazing eye" by local people, as shown in Figure 21-Z-3. According to reports, the larger the diameter of a radio telescope, the higher its sensitivity, and the richer the universe information it can search for. Previously, the world's largest radio telescope was the Arecibo 305-meter telescope in Puerto Rico developed by the United States. With the completion of the world's largest single-diameter radio telescope in my country, China has maintained its leading position in radio astronomy in the world in a short period of time.

Although FAST is a radio telescope, it does not like to be in an environment with electricity. Even the smallest radio wave is unbearable. The chief engineer of the FAST project of the National Astronomical Observatory of the Chinese Academy of Sciences once said vividly that not to mention using mobile phones, even if electrical appliances are used nearby, or if an aircraft sends information to the ground dozens of kilometers away, an electromagnetic storm will be caused at FAST. As a radio telescope, the basic principle of FAST is almost the same as that of the common pot-type satellite antenna. The "pot" of FAST is larger. The main reflecting surface covers an area of ​​250,000 square meters. It is mainly composed of a paraboloid that reflects signals and a feed that receives signals. It consists of two parts: the source. Through the reflection and focusing of the "pot", the signal from several square meters to thousands of square meters is gathered to one point.

Radio waves that are projected from celestial bodies and focused on the focus of a telescope. Radio waves are actually part of radio waves. The earth's atmosphere absorbs most of the electromagnetic waves from the universe. Only visible light and some radio waves can penetrate the atmosphere. In astronomy, these radio waves are called radio waves.

please answer the following question:

(1) A mobile phone is a mobile communication tool that uses ______ waves for long-distance information transmission. When the radio telescope is working normally ______ (optional "can" or "cannot") use a mobile phone.

(2) The propagation speed of radio waves in vacuum is ______m/s.

(3) Radio telescopes use electromagnetic waves to generate ______ to collect signals.

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