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

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

The propagation of television signals relies on electromagnetic waves

Mobile phones rely on electromagnetic waves to transmit information

How are electromagnetic waves generated?

How do electromagnetic waves propagate?

What is the relationship between wavelength, wave speed, and frequency?

1. Generation of electromagnetic waves

listen

Radio: makes a "click" sound

Electromagnetic wave generation demonstration experiment

Conclusion Rapidly changing electric current can produce electromagnetic waves in the surroundings.

Essence: Electromagnetic field energy spreads from near to far.

Oscillating current

Concept: Specialized electronics and circuits are used to generate electrical current that changes very quickly.

Oscillating current is a periodically changing current. The speed of change is expressed by frequency, and the unit of frequency is Hertz (Hz). There are also kilohertz (kHz), megahertz (MHz), gigahertz (GHz).

1kHz=103Hz

1MHz=106Hz

1GHz=109Hz

2. Propagation of electromagnetic waves

The propagation of sound requires solid, liquid, gas and other media.

Does the propagation of electromagnetic waves require a medium?

small experiment

Put a mobile phone into the vacuum cover and dial the number of the mobile phone. Does the phone respond?

in conclusion

The propagation of electromagnetic waves does not require a medium.

1. Electromagnetic waves can propagate in a vacuum

2. Several elements of electromagnetic waves

(1) Wavelength: the distance between two adjacent wave crests (or troughs).

Unit: m

(2) Wave speed: how fast the wave propagates. Unit: meters/second

3． propagation speed of electromagnetic waves

In vacuum: c =2.997 924 58 ×108 m/s

In air: close to the speed of light in vacuum

Light is an electromagnetic wave

Class summary

Rapid changes in current in a wire can stir up electromagnetic waves in space.

Electromagnetic waves can propagate in media as well as in vacuum.

The propagation speed of electromagnetic waves in vacuum

c =2.997 924 58×108 m/s ≈3×105 km/s

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Update Time: 2024-11-24

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

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