"Linear Propagation of Light" Light Phenomenon PPT Courseware 4

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"Linear Propagation of Light" Light Phenomenon PPT Courseware 4

1. Light source: an object that can emit light on its own

Such as: sun natural light source

Candles, lamps, flashlights, etc. Artificial light sources

2. Propagation of light

1. Demonstration experiment:

Use a laser pointer to shoot into a container filled with smoke and observe the path of light propagation. What can we see about the propagation of light in the air?

Conclusion: Light propagates along ( ) in ( ) medium.

2. Light: a straight line indicating the propagation direction of light

3. Applications and examples of straight line propagation of light

A. Laser alignment (using laser to guide tunnel boring machine)

(Characteristics of laser: It can be concentrated in one direction without scattering, so it can shoot very far without obvious reduction in brightness)

B. When lining up, look forward

C. Formation of shadow: Since light propagates along a straight line, when light encounters an opaque object during propagation, a shadow is produced behind the object.

(1) Causes of shadow formation

During the propagation process of light, it encounters an opaque object. Since light propagates in a straight line, the light cannot reach the back of the opaque object, and the dark part is the shadow of the object.

4 Propagation of light

The propagation of light does not require a medium

B The propagation speed of light in vacuum C= 3×108m/s

The speed of light propagating in water is three-quarters of that in a vacuum.

The propagation speed in glass is two-thirds that in vacuum

The distance that light travels in the air in 1 second is equivalent to 7.5 times around the earth. It only takes 1.3 seconds for light to travel from the moon to the earth.

Want to discuss:

Can you think of a way to estimate how far away a lightning strike is from you?

Answer: (ignore the propagation time of light)

After seeing lightning, immediately look at your watch and note the time; wait a few seconds before hearing thunder.

Using the speed of sound in the air, the distance to the lightning can be found according to s=vt.

practise:

1. 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

2. 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. This can be explained by __________.

3. 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: 2024-11-18

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

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