"The Fastest "Messenger"" Electromagnetic Waves and the Information Age PPT Courseware 2

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"The Fastest "Messenger"" Electromagnetic Waves and the Information Age PPT Courseware 2

think about it

It is impossible for the pilot on the plane to communicate with the ground commander using wires, so how do they communicate?

We listen to the radio or watch TV every day, and there are no wires directly connected to the radio or television station. How do we receive the signal?

1. Generation of electromagnetic waves

Experiment: Existence of electromagnetic waves

Near an open radio, place the negative terminal of the battery in good contact with a file. Connect the positive terminal to a wire. Hold the wire ends so they are in contact with the file and slide them over the surface of the file.

Question: Why does a radio working nearby make a "click-click" sound?

When there is a rapidly changing current (oscillating current) somewhere in a conductor or circuit, an electromagnetic oscillation will be generated there, and electromagnetic waves propagating outward will be generated in the surrounding space.

2. Wavelength, frequency and wave speed

The wavelength, frequency and wave speed of electromagnetic waves satisfy:

c=λf

The frequency of an electromagnetic wave is determined by the number of changes in direction of current in a conductor per second.

German physicist Hertz experimentally confirmed that the propagation speed of electromagnetic waves is equal to the speed of light, that is, 3×105 km/s in a vacuum. The propagation speeds of electromagnetic waves of different frequencies are the same, and electromagnetic waves with higher frequencies have shorter wavelengths.

3. Characteristics of electromagnetic waves

Electromagnetic waves propagate in all directions in space.

The propagation speed of electromagnetic waves is equal to the speed of light, which is similar in air and in vacuum.

Electromagnetic waves of different frequencies (or different wavelengths) propagate at the same speed, so electromagnetic waves with higher frequencies have shorter wavelengths.

Sound waves and water waves must have a propagation medium, but the propagation of electromagnetic waves does not require other media and can propagate in a vacuum. This is one of the major differences between electromagnetic waves and sound waves.

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For more information about the PPT courseware "Electromagnetic Waves and the Fastest Messenger in the Information Age", please click the "Electromagnetic Waves and the Fastest Messenger in the Information Age" ppt tag.

"The Fastest "Messenger"" Electromagnetic Waves and the Information Age PPT courseware:

"The Fastest Messenger" Electromagnetic Waves and the Information Age PPT Courseware Learning Objectives 1. Know what electromagnetic waves are 2. Know the characteristics of electromagnetic waves 3. Understand the application of electromagnetic waves in life 1. Experience electromagnetic waves Activity 1: Electromagnetic waves around us Turn on the radio and turn the tuner ..

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Update Time: 2024-10-19

This template belongs to Physics courseware Guangdong and Shanghai Edition Ninth Grade Physics Volume 2 industry PPT template

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