"Light World Tour" Light and Eyes PPT Courseware 2

"Light World Tour" Light and Eyes PPT Courseware 2

learning target

1. Know some uses of light and that light is closely related to human life.

2. Know that light propagates along straight lines in the same homogeneous medium and can be used to explain phenomena such as the formation of shadows.

3. Understand that light propagates at the maximum speed in vacuum, and remember the speed of light in vacuum

4. Through dispersion experiments, we know that white light is composed of seven colors of red, orange, yellow, green, blue, indigo, and violet. Knowledge of what are the three primary colors of light.

Core test points: linear propagation of light, dispersion of light.

Preview before class

1. Light source: Objects that can _____ themselves are called light sources. The sun and fireflies are _____ light sources, and bonfires, candles, oil lamps, electric lamps, etc. are _____ light sources.

2. Propagation law: Light propagates along _______ in the same uniform medium. Examples of linear propagation of light in daily life include: __________, __________, _______, etc.

3. Speed ​​of light: The speed of light is different in different _____. The speed of light is maximum in _____. The speed of light in vacuum is C=_____.

4. Look out through the crack in the door. The closer your eyes are to the crack (fill in "near" or "far"), the larger the observed range. This can be explained by the __________ of light.

5. Dispersion: Sunlight is decomposed into _______________ after passing through a prism, indicating that white light is mixed from __________.

6. The three primary colors of light: _____, _____, _____. The three primary colors of pigments are _____, _____, _____.

Lectures in class

Knowledge point 1. Light source

A light source is an object that can emit light by itself. Note: Objects that cannot emit light by themselves are not light sources. For example, the sun is a light source, but the moon is not a light source.

Light sources can be divided into two categories: natural light sources and artificial light sources. Natural light sources include: the sun, stars, erupting volcanoes, lantern fish in the deep sea, ax fish, etc.; artificial light sources include: lit candles, working electric lamps, Work computer monitor and more.

[Example 1] Among the following objects, all of them are light sources ( )

A. Dazzling glass wall, burning matches, fireflies

B． Bonfire, glowing light bulbs, stars in the night sky

C. Fireflies, flames of kerosene lamps, brilliant diamonds

D． Glowing light bulb, burning bonfire, sun

[Exercise 1] Which of the following objects or animals is the source of light ( )

A. Brilliant diamond b. Jellyfish c. moon d. reflector

Knowledge point 2. How light spreads

In the same homogeneous medium or in a vacuum, light propagates along a straight line. For example: the formation of solar and lunar eclipses, the formation of shadows, small hole imaging, three points and one line to hit the target when shooting, laser collimation, standing in column If you can only see the back of a classmate's head, it means that the line is straight, etc. This is all because light travels in a straight line.

Shadow: Shadows will appear under light, sunlight or moonlight, which proves that light travels in a straight line in the air. If light can turn, it can go around the object and run behind the object, and the backlight of the object will be bright. If you get up, there will be no shadow.

Solar eclipse: When the sun, moon, and earth turn in a straight line, if the moon blocks the sun's light in the middle, so that people on the earth in the moon's shadow area cannot see the complete sun, a solar eclipse occurs.

Lunar eclipse: When the sun, moon, and earth turn in a straight line, if the earth blocks the sun's light in the middle, so that the moon is completely or partially in the shadow area of ​​the earth, and people cannot see the complete moon, a lunar eclipse occurs.

Since light propagates along straight lines, we can draw a straight line along the propagation route of light, and draw arrows on the straight line to indicate the direction of light propagation. This straight line representing the propagation direction of light is called a ray. As shown below:

Note: Light does exist, but light is introduced by people in order to describe the propagation direction and path of light. Light does not exist. This research method is called the physical model method.

Knowledge point 3. speed of light

Light can travel in a vacuum, or in a gas, liquid, or solid.

The maximum speed of light in vacuum: c=3×108m/s. Usually the speed of light in gas is greater than the speed of light in liquid, and the speed of light in liquid is greater than the speed of light in solid. (This is contrary to the speed of sound, sound cannot Propagation, usually the speed of sound in gas is smaller than the speed of sound in liquid, and the speed of sound in liquid is smaller than the speed of sound in solid. Be sure to compare and remember!)

The speed of light in air is very close to the speed of light in vacuum, which can also be regarded as 3×108 m/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 the speed of light in vacuum. 2/3．

The distance that light travels in one year is the astronomical unit of length. 1 light year=9.46×1010km.

[Example 3] Regarding the speed of light, which of the following statements is incorrect ( )

A. The propagation speed of light is always 3.0×108 m/s

B． The maximum propagation speed of light is 3.0×108m/s

C. Light year is a unit of length

D． Light year is an astronomical unit of distance

[Exercise 3] (2014·Fujian) The propagation speed of light in vacuum is about ( )

A. 340m/s b. 340km/s

C. 3×108m/s D. 3×108km/s

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"Light World Tour" Light and Eyes PPT Courseware:

"Light World Parade" Light and Eyes PPT Courseware Teaching Objectives 1. Understand the role of light and know that light is closely related to human beings. 2. Knowing that light propagates along a straight line in the same uniform medium, we can use the law of straight line propagation of light to explain the phenomenon of shadow formation. 3. Know...