"Propagation of Light" Light Phenomenon PPT Courseware 4

Description

"Propagation of Light" Light Phenomenon PPT Courseware 4

Knowledge and Skills Objectives

1. Understand the light source, the propagation rules of light, phenomena and applications.

2. Know the speed of light in vacuum

3. Be able to use light to represent the propagation path of light.

1. Light source: Objects that can emit light are called light sources.

1. Natural light source: sun, stars, etc.

2. Artificial light source:

Information Integration

glowing object

natural light source

Stars such as the sun, fireflies, glowing fish, and jellyfish

artificial light

Glowing incandescent lamps, lit candles, neon lights, blooming fireworks,

think about it

Is the moon a source of light? Is it true to say "candles are a source of light"?

Ask a question

How does light travel?

conjecture hypothesis

hint:

●In what materials can light propagate?

●What is the propagation path of light?

Experimental exploration

1. Light spreads in the air

2. Light spreads in water

3. Light propagates in glass

2. Straight line propagation of light:

3. Light:

1. Draw a straight line along the propagation path of light

2. Draw an arrow on the straight line to indicate the direction of light propagation.

3. This straight line with an arrow indicating the propagation direction of light is called a light ray.

4. Example: Draw a ray diagram of a parallel light source.

5. Exercise: Please draw the light diagram of a point light source.

Discuss

Does light always propagate in straight lines in the same medium?

What we see when the sun rises in the morning

Observe and communicate

What conditions do the above phenomena need to satisfy when light propagates along a straight line in the same medium?

Analyze arguments and draw conclusions

Light propagates along straight lines in the same homogeneous medium

pinhole imaging

Since light propagates along a straight line, the light emitted from above the object is projected below through the small hole, and the light emitted from below the object is projected above through the small hole, thus forming an inverted real image. When the position of the small hole is fixed, the farther the object is from the screen, the smaller its image will be, and vice versa, but in either case, the image will be inverted.

5. The speed of light:

1. The speed of light in vacuum is 299792458m/s, which is approximately equal to 3×108m/s.

2. The speed of light in air is about 3×108m/s;

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

4. Think about it: Thunder and lightning happen at the same time. Why do we always see lightning first and then hear thunder?

Examine the questions carefully, answer the questions carefully, and perform well

1. Fireflies, the moon and movie screens all look bright. Among them, the light source is _____.

2. In order to check whether a piece of wood is straight, carpenters often use the following method: close one eye and use the other eye to look along the direction of the edge. This makes use of _____.

3. It takes 500 seconds for sunlight to travel to the earth. It can be seen that the distance from the sun to the earth is _____ km.

4. Lightning and thunder happen at the same time. The reason why we see lightning first and then hear thunder is _______.

5. Many magical natural imaginations are related to shadows, such as the formation of a solar eclipse. As shown in the picture, people can see _____ in area 1, _____ in area 2, and _____ in area 3. arrive_____ .

Use your imagination

Scientists imagine that humans may move to the moon in the future. If this is possible, will residents on the moon still be able to see solar and lunar eclipses?

Tip: A solar eclipse may occur when the Earth passes between the sun and the moon

Use your intelligence; show your talents!

Quality assessment:

1. Light propagates along _______ in a uniform medium.

2. The propagation speed of light in _______ is the largest, and its value is _______m/s.

3. The figure under the lamp is formed by _______.

4. Which of the following statements is correct ( )

A. Light travels in straight lines in any medium.

B. The light emitted by the sun travels in a straight line when it hits the earth.

C. Pinhole imaging shows that light propagates in a straight line in a uniform medium.

D. The speed of light in water is greater than the speed of light in vacuum.

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Update Time: 2024-11-13

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