People's Education Press Fourth Grade Science Volume 2

Description

"The Source and Propagation of Light" Wonderful Light PPT Courseware

self-guided study

1. What is a light source? What categories does it fall into?

2. How does light spread?

3. What is the propagation speed of light in vacuum? What about in water and glass?

4. What does light year mean?

1. Light source: an object that can emit light

Give it a try:

The sun, moon, and lit torches are ___ that are sources of light.

2. Propagation of light

Light propagates along straight lines in the same homogeneous medium

Draw light: straight lines, arrows

When light propagates in a straight line, it encounters an opaque object and produces an impact behind the object.

Small hole imaging characteristics

1. Like the image of an object. The shape of the image has nothing to do with the shape of the hole, only the object.

2. The image is inverted

3. The image can be enlarged or reduced. The farther the screen is from the hole, the larger the image will be.

4. The image is a real image

Give it a try:

Which of the following phenomena does not mean that light propagates in a straight line ( )

A. Standing by the river and seeing the reflection of the mountains

B. The scene at the other end cannot be seen through the curved empty iron pipe.

C. A partial solar eclipse occurred in Wuhan in May this year

D. Standing under the street light, shadows of people appear on the ground

Think about it:

When thunder strikes, why do we always see lightning first and then hear thunder?

When thunder strikes, how do we estimate the distance from where lightning strikes?

When the timekeeper of the 100-meter race sounds the starting gun, when does the timer start timing and why? ( )

A. Timing when you hear the gunshot, because this way the timing error is small

B. When you see smoke coming from the gun, time it because the smoke is more obvious.

C. Time the sound when you hear the gunshot, because you can hear the gunshot more clearly.

D. When you see smoke coming from the gun, time it because the speed of light is much greater than the speed of sound.

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For more information about the "Wonderful Light Source and Spread of Light" PPT courseware, please click the Wonderful Light ppt Source and Spread of Light ppt tag.

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Update Time: 2024-07-03

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