"The Ocean of Electromagnetic Waves" Information Transmission PPT Teaching Courseware

"The Ocean of Electromagnetic Waves" Information Transmission PPT Teaching Courseware

Part One: Guidance Design

Learning point 1: Understand electromagnetic waves

As shown in Figure 21-2-2, turn on the switch of the radio, turn it to the position where there is no radio station, and turn up the volume. Take a dry cell battery and a lead and hold them near the radio. First connect one end of the wire to the negative terminal of the battery, and then rub the other end of the wire against the positive terminal of the battery so that they are in intermittent contact.

Question: The radio makes a "click" sound, indicating that the radio has received __________. The reason is that when the wire is in intermittent contact with the battery, the ____________ in the circuit changes rapidly at the moment of being turned on and off, and __________ is emitted.

Learning point 2: Propagation of electromagnetic waves

Question 1: In a series of waves, the most ______ place that is convex is called the crest, and the most ______ place that is concave is called the trough. The distance between two adjacent ________ (or ________) is called the wavelength. At a certain position, the ________ of the wave is how many times the wave peak or wave trough passes within 1 s. The physical quantity used to describe wave propagation ________ is called wave speed.

Question 2: Make a call to the mobile phone in the vacuum hood. This mobile phone ________

(Optional "can" or "cannot") Signal received. It can be seen that electromagnetic waves ________(optional "" or "cannot") propagate in vacuum, which shows that the propagation of electromagnetic waves______

(Optional "required" or "unnecessary") medium, its propagation speed is _________.

Question 3: Electromagnetic waves are a large family. Light is a kind of electromagnetic wave.

Ocean PPT of Electromagnetic Waves, Part 2: Summary of Frequent Examinations

Type 1 Generation of electromagnetic waves

Typical Example 1 (Multiple Choice) In order to test the generation of electromagnetic waves, students from a certain experimental group connected several circuits as shown in Figure 21-2-6. When they placed the turned on radio near the circuit, they could detect the electromagnetic waves. What is produced is ( )

Type 2 Propagation of electromagnetic waves

Typical example 2 The frequency range of a certain mobile phone network is 1920 MHz ~ 1935 MHz. Which of the following statements is correct ( )

A. The electromagnetic wave wavelength of 1920 MHz is shorter than that of 1935 MHz

B． 1920 MHz electromagnetic waves cannot propagate on the moon without air

C. The electromagnetic wave of 1920 MHz propagates slower in vacuum than the electromagnetic wave of 1935 MHz.

D. Electromagnetic waves at 1920 MHz and 1935 MHz travel at the same speed in vacuum

[Method Breakthrough] ① Under the condition that the electromagnetic wave speed is certain, the higher the frequency, the shorter the wavelength. ②Electromagnetic waves of different frequencies propagate at the same speed in the same medium; electromagnetic waves of the same frequency propagate at different speeds in different media.

Type 3: Understand the waveform of electromagnetic waves

Typical Example 3 Figure 21-2-7 shows the propagation images of two different electromagnetic waves A and B. Their frequencies are fA and fB respectively, then fA ________ fB. Their propagation speeds in vacuum are vA and vB respectively, then vA________vB. (Please fill in “＞”, “=" or “＜”)

Type 4 Uses of electromagnetic waves

Typical Example 4 Give the following four examples of the application of electromagnetic waves in daily life and production. (Give at least one example of each type of electromagnetic wave) Example:

(1) Infrared: The TV remote control uses infrared rays for remote control.

(2) Radio waves: _______________________________.

(3) Microwave: _______________________________.

(4) Ultraviolet light: _______________________________.

(5) X-ray: _______________________________.

Ocean PPT of Electromagnetic Waves, Part 3: Class Feedback

1. As shown in Figure 14-1, turn on the radio switch, adjust the knob to the position where there is no radio station, and turn up the volume. Take an old dry battery and a wire, put it close to the radio, connect one end of the wire to the negative terminal of the battery, and then use the other end of the wire to make __________ friction contact with the positive terminal of the battery. You will hear the radio making a "click" sound. " or "click" and other noises, this phenomenon verifies the existence of ________.

2. Among the following statements about electromagnetic waves, which one is correct ()

A. Electromagnetic waves cannot propagate in a vacuum

B． The propagation speed of electromagnetic waves in the air is about 3×108 km/s

C. Mobile phones rely on electromagnetic waves to transmit information

D. Refrigerators use electromagnetic waves to work

3. One rainy day, Xiao Ming was listening to the radio station at home. Xiao Ming discovered that when there was lightning and thunder, he would hear a "click" sound from the radio, and then he would hear thunder. Lightning can stimulate ________, and the radio receives the signal and makes a "click" sound. As shown in Figure 14-2, move the station pointer from left to right, the wavelength of the electromagnetic wave received by the radio becomes ________ (optional "long" or "short").

4. The electromagnetic wave family includes radio waves, infrared rays, visible light, ultraviolet rays, etc. They have the same ________ (optional "frequency", "wavelength" or "wave speed") in the same medium, and their speed when propagating in a vacuum is about ____________ .

5. The discovery and application of electricity and magnetism have brought many conveniences to mankind. We live in a sea of ​​electromagnetic waves. The waveform of a certain electromagnetic wave is shown in Figure 14-3. The wavelength of the electromagnetic wave is ________m and the frequency is ________Hz.

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