"Linear Propagation of Light" Light Phenomenon PPT Courseware 6

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"Linear Propagation of Light" Light Phenomenon PPT Courseware 6

1. Light source

1. Light source: An object that can emit light is called a light source.

2. Light sources are divided into two categories: natural light sources and artificial light sources.

Natural light sources: stars (such as the sun), fireflies, luminous jellyfish, etc.

Artificial light sources: electric lamps, flashlights, bonfires, torches, lit candles and oil lamps, etc.

2. Propagation of light

The beams of light among the trees were very straight strips of light;

The light beams of the ornamental lights on the square are very straight beams of light.

Through observation, we found that light seems to be straight.

1. Exploration activities. How does light travel?

Experiment 1: How does light propagate in the air?

Spray a large amount of water mist into the air, use a laser pointer to shoot a beam of light in the water mist, and observe the path of light propagation;

Explanation of the experimental phenomenon: Light propagates ______ in the air.

Experiment 2: How does light propagate in water?

Add a small amount of milk to the water, use a laser pointer to emit a beam of light in the water, and observe the path of the light propagation;

Explanation of the experimental phenomenon: Light also propagates ______ in water.

3. Speed ​​of light

Read page 71 of the textbook; answer the following questions:

1. Thunder and lightning happen at the same time and in the same place. Why do we always see the lightning first and then hear the thunder?

2. What are the differences in the propagation of light and sound?

3． How fast does light travel in a vacuum?

4. Are the propagation speeds in other transparent media faster or slower than those in a vacuum?

The propagation speed of light in vacuum: c=3×108m/s

The propagation of light does not require a medium

The speed of light in a vacuum is the fastest speed in the universe

Speed ​​in air: about 3×108 meters/second

The speed in water is 3/4 of the above value and in glass is 2/3 of the above value

If a flying man orbits the earth at the speed of light, he can orbit the earth 7.5 times in 1 second.

It takes about 8 minutes for the light from the sun to reach the earth. If a 1000km/h racing car runs non-stop, it will take 17 years to complete the distance from the sun to the earth!

Class exercises:

1. Light travels along __________.

2. The formation of shadow indicates __________.

3. The propagation speed of light in vacuum is __________.

The speed of propagation is __________ than in other media. (speed)

4. When light is ejected from air into water, its speed will be ( )

A. Faster B. Slower C. No change

5. Which of the following objects is a light source ( )

A. The moon B. Fireflies C. Stars at night

D. Polished metal that shines under the sun E. Mirror

6. When lining up in a column, if you see a classmate in front of you blocking all the people in front of you, the line will be straightened. This can be explained by ______________.

7. When a person walks along the street towards the street lamp, and then walks away from the street lamp, the change in the length of his shadow is ( )

A. Become longer B. Become longer first and then become shorter

C. become shorter D. first become shorter and then longer

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Update Time: 2024-09-06

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 1 industry PPT template

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