"Dispersion of Light" Light Phenomenon PPT Courseware 6

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"Dispersion of Light" Light Phenomenon PPT Courseware 6

1. Dispersion

Why do rainbows appear in the sky?

After sunlight passes through a prism, it is decomposed into light of various colors. This phenomenon is called dispersion of light.

White light is a mixture of seven monochromatic lights: red, orange, yellow, green, blue, indigo, and violet.

Experiments have shown that the three colors of red, green and blue light in nature cannot be mixed with light of other colors, so these three colors are called the three primary colors of light.

Other lights can be obtained by properly mixing these three colors of light.

2. Mixing of colors and lights

It was discovered that three monochromatic lights, red, green, and blue, mixed in different proportions, can produce light of various colors. The three primary colors of light are: red, green, and blue.

The color of the TV picture is composed of three color bars: red, green and blue.

3. Invisible light

1.Spectrum

A prism can decompose sunlight into seven colors of light: red, orange, yellow, green, blue, indigo, and violet. Arranging them in order is a spectrum.

Experiment summary

Have you observed any changes in the thermometer readings in different areas?

What do these phenomena illustrate?

There may be some invisible light outside the red light.

The method of studying things that cannot be directly perceived through their various effects is called conversion method.

Characteristics of infrared rays

Infrared rays have a thermal effect and can cause the irradiated object to heat up.

The sun's heat is mainly transmitted to the earth in the form of infrared rays.

Objects can absorb infrared rays and also radiate infrared rays.

All objects are constantly radiating infrared rays, and objects with different temperatures emit infrared rays at different intensities. The higher the temperature of an object, the more infrared rays it radiates.

Characteristics and applications of ultraviolet light

The most remarkable feature of ultraviolet light is that it can make fluorescent substances glow.

Ultraviolet rays can kill microorganisms, and ultraviolet rays can sterilize.

Ultraviolet rays and human life

Ultraviolet rays are closely related to human life and health. Moderate ultraviolet radiation is good for health, and ultraviolet rays help the body synthesize vitamin D.

Excessive ultraviolet radiation can harm human health, ranging from rough skin to skin cancer. So you must pay attention to protection.

3. Color of objects

If there is no light, we live in darkness, can we still see various colors of objects? All objects look black.

When light shines on the surface of an object, part of the light is reflected by the object, part of the light is absorbed by the object, and if the object is transparent, part of the light passes through the object. Different objects reflect, absorb, and transmit light of different colors. Different, therefore appear in different colors.

1. Color of transparent objects

1. When white light shines on red glass, the red glass can only transmit red light, so it looks red.

2. When white light shines on blue glass, the blue glass can only transmit blue light, so it looks blue.

3.Why do the classroom windows look transparent?

Because the classroom windows can pass through all colors of light, they appear transparent.

The color of a transparent object is determined by the colored light it transmits.

2. Color of opaque objects:

Because red objects only reflect red light and absorb all other colors of light, they look red.

Similarly, blue objects only reflect blue light and absorb other colors of light, so they look blue.

The color of an opaque object is determined by the colored light it reflects.

Black: Black objects absorb all colored light. It cannot reflect any colored light, so it looks black.

White: White objects reflect all colors of light, so they look like a composite color: white.

Colorless: If an object can transmit all colors of light, the object is colorless and transparent.

practice

1. Excessive sun exposure can make the skin rough and even cause skin cancer. This is caused by what kind of light in the sun ( )

A. Infrared ray B. Ultraviolet ray C. Visible light D. None of the above

2. Which of the following statements is correct ( )

A. All light can be seen by people

B. Ultraviolet rays are purple

C. There are only two types of invisible light: infrared and ultraviolet.

D. Light is actually an electromagnetic wave

3. The small transistor lasers on the market emit red light, so many people call it "infrared". Do you think this is correct? Why?

4. The light emitted by the currency detector is light blue, so some students think that ultraviolet light is light blue. Is this correct? Why?

5. People always put their clothes and quilts in the sun every once in a while. This is good for health. Let’s talk about the reasons for doing this based on the physics knowledge we have learned.

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Update Time: 2024-07-09

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

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