"Linear Propagation of Light" Light Phenomenon PPT Courseware 7

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"Linear Propagation of Light" Light Phenomenon PPT Courseware 7

Colorful light phenomena

1. What is a light source?

2. How does light propagate? How to express the propagation route of light?

3. What are the applications of light propagation?

4. How fast does light travel?

5. The world of science: light years

1. Light source

1. What is a light source?

The picture above shows various light sources in life and production. Could you please analyze their common characteristics?

Conclusion: Objects that can emit light themselves.

2. Classification of light sources

Classify the light sources above according to whether they emit light naturally or not.

Conclusion: Light sources can be classified into natural light sources and artificial light sources.

2. Straight line propagation of light

tips

We see objects because the light emitted or reflected by the objects enters our eyes.

1. How does light spread?

2. Light

In order to represent the propagation of light, we usually use a straight line with an arrow to represent the path and direction of light. Such straight lines are called rays.

We know that sound cannot travel through a vacuum.

So can light travel in a vacuum?

Light can propagate in a vacuum and its propagation speed is the fastest.

3. Phenomenon explained by light propagating along straight lines

After learning about the linear propagation of light, you should be able to use this knowledge to explain some physical phenomena, improve your understanding of nature and your ability to solve practical problems.

3. The propagation speed of light

The speed of light propagating in the same uniform medium is constant, but the speed of light propagating in different media is different. The speed of light in vacuum is the largest, represented by the letter c. The speed of light in various other media is faster than that in vacuum. is small. When calculating, the speed of light in vacuum and air is taken as C=3×108m/s

The speed of light in water is about 3/4 of the speed of light in vacuum, and the speed of light in glass is about 2/3 of the speed of light in vacuum.

we saw the ancient light

think:

1. What physical quantity is the unit of light year?

2. Why can we see ancient light?

3.The distance between Altair and Vega is 16.4 light years

Summary of this section

1. An object that can emit light is called a light source. Light sources are divided into natural light sources and artificial light sources.

2. Conditions for light to propagate along straight lines: Light propagates along straight lines in the same homogeneous medium.

3. Use a straight line with an arrow to represent light, which indicates the propagation route and direction of light.

4. The propagation speed of light in vacuum is the largest, and its size is c=3x108m/s.

5. Light year: equal to the distance that light travels in 1 year. Light year is a unit of length.

Class exercises

1. Objects that can emit light are called ______. It can be divided into two categories: ______ and ______. Among them, the electric light is ______, and the sun is ______.

2. Light propagates along ______ in the same homogeneous medium. The propagation of light is ______ medium.

3. Since light propagates along a straight line, phenomena such as ______, ______, ______, ______ are formed.

4. When digging a mountain tunnel, the laser beam is used to guide the boring machine forward, using the ______ principle.

5. Light travels fastest in ______, and the speed in air is close to it. In our calculations, the speed of light in vacuum or air is taken as C=______.

6. When lining up, if you see a classmate in front of you blocking all the people in front of you, the line will be straightened up. This can be explained by ____________. When practicing shooting, you need to "three points and one line" to shoot. To be accurate, that is, the notch on the scale on the gun, the front sight on the gun, and the shooting target must coincide. This is based on __________.

do you know?

1 light year distance

Solution: 1 year = 1x365x24x3600s = 31536000s

1 light year =31536000sx3.0x105km/s=9.46x1012km

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Update Time: 2024-10-07

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

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