"Propagation of Light" PPT courseware on light phenomena 6

Description

"Propagation of Light" PPT courseware on light phenomena 6

1: Concept of light source

Objects that can emit light by themselves are called light sources.

2: Example

The sun, stars, turned on electric lamps, lit candles, fireflies, and the liquid crystal on the electronic watch are the sources of light.

The moon, gems, luminous pearls, and the screen showing a movie are not sources of light.

Artificial light sources have a long history. Since people were able to use fire, cave-dwelling primitive people relied on campfires for lighting, and later gradually learned to use torches. During the Warring States Period about 2,000 years ago, oil lamps were used for lighting, and candles were later invented. In 1878, Edison invented the modern electric light. Electric lights were introduced to my country at the beginning of the 20th century and spread to all regions of the world over the past 100 years. Current lamps include incandescent lamps, fluorescent lamps, shadowless lamps, news lamps, etc.

Conclusion: Light propagates in straight lines in the same homogeneous material.

Example: The formation of shadows

Solar eclipse, lunar eclipse

Aiming practice with a rifle

pinhole imaging

The distance between the sun and the earth is about 1.5×108 kilometers. It takes 8 minutes and 20 seconds for sunlight to reach the earth. Calculate how far the light travels per second?

V=S/t=1.5×108 kilometers/500 seconds=3×105 kilometers/second

research shows:

Light travels at different speeds in different materials.

The propagation speed of light in vacuum is 3*105 kilometers/second. And it spreads fastest in a vacuum.

The distance that light travels in one year is approximately equal to 9.46×1012 kilometers, and this length is called 1 light year.

summary:

What is a light source?

Objects that can emit light by themselves are called light sources.

What is the propagation route of light?

Light propagates in straight lines in the same homogeneous material.

How fast does light travel?

Light travels at different speeds in different materials.

The propagation speed of light in vacuum is 3×10 kilometers/second. And it spreads fastest in a vacuum.

The speed of light in air is very close to the speed in vacuum

The speed of light in water is about three-quarters of that in air

The speed of light in glass is about two-thirds that in air

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Update Time: 2024-10-19

This template belongs to Physics courseware Beijing Normal University eighth grade physics volume one industry PPT template

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