How "Electromagnetic Waves" Transmits Information—Introduction to Communication Technology PPT Courseware 3

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How "Electromagnetic Waves" Transmits Information—Introduction to Communication Technology PPT Courseware 3

1. Basic characteristics of waves:

1. Activities:

The water waves are alternately concave and convex, spreading outward.

The rope waves are alternately concave and convex, propagating to the other end

The common points are concave and convex, spread outwards

2. Observation: What happens when the suspended spring is hit

Phenomenon: The spring transmits a movement pattern of alternating density and density.

Compare: What do the different forms of waves have in common?

All waves propagate periodically changing motion patterns.

3. Characteristic physical quantities of waves

Amplitude (m): The maximum distance the wave source deviates from the equilibrium position. Represented by A.

Reflects the strength of the wave source vibration.

Period (s): The time it takes for the wave source to vibrate once. Indicated by T.

Frequency (Hz): The number of times the wave source vibrates per second. Represented by f.

Wavelength (m): The distance the wave travels in one period T. Represented by λ.

Wave speed (m/s): The propagation speed of waves. Represented by v.

2. Understand electromagnetic waves

question:

1. Who predicted the existence of electromagnetic waves?

2. Who first experimentally verified the existence of electromagnetic waves?

3. What are electromagnetic waves?

Electromagnetic waves are periodically changing electromagnetic fields that propagate in space.

Activity: Verify the existence of electromagnetic waves

Equipment: radio, dry batteries, wires

step:

1. Turn on the switch of the radio, adjust the knob to the position where there is no station, and increase the volume.

2. Connect one end of the wire to one pole of the dry battery, and then connect the other end of the wire intermittently.

3. What did you hear on the radio? why is that?

3. Electromagnetic Spectrum

Application of electromagnetic waves - microwave oven

Microwave frequency: 2450MHz

Advantages: fast cooking, no fumes, less loss of food nutrients, and clean.

Principle: When microwaves are irradiated onto food, the moisture in the food vibrates at the same frequency. During vibration, molecules rub against each other, generating a lot of internal energy.

Give it a try • Think about it • Take a look

Why are the linings of microwave ovens made of metal?

There is a transparent glass inlaid on the door of the microwave oven. Aren't you afraid that the microwave will "escape" through the glass? Please carefully observe the metal grid attached to the glass panel and analyze its function.

Dangers of electromagnetic waves

"Science and Technology Daily" once introduced:

●Of the 20 million children born every year in our country, 350,000 are deficient, of which 250,000 are intellectually deficient. Electromagnetic wave pollution poses the greatest threat.

●In Maryland, USA, 951 men died of brain tumors from 1969 to 1982. Most of the deceased were electronic engineers and frequent users of "Big Brother".

●When Nicholas, the famous chess master of the former Soviet Union, was playing chess with a supercomputer, he suddenly died after winning three games in a row. The killer was the electromagnetic waves released by the computer.

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Update Time: 2024-10-20

This template belongs to Physics courseware Beijing Normal University Ninth Grade Physics Volume 2 industry PPT template

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