Straight line propagation of light 15, straight line propagation of light

Assuming that the lamp is x meters high, the small people start from the lamp y meters

1) At the beginning, the shadow of the small people is long meters, and the small people are parallel to the lamp, there are.

2) After 2 seconds, the shadow length changes to 2 meters, and at the same time it moves 2 meters, and the small people are still parallel to the lamp, and then there is.

2/(2+2+y)= ..2)

Solve the equations (1) and (2) to obtain y 6 meters, x meters.

So the length of the lamp is meters

Set the height of the lamp x, and the distance between the position of the first person standing and the lamp is aA schematic diagram will be used to find out.

It can be listed according to the triangular ratio: x (a + simplified x = after the person leaves 2 meters, then another triangular relationship is obtained: x (a+2+2)= simplified x = x = m is obtained.

So the height of the lamp is meters.

Solution: The street lamp is x meters long, and the small people are originally y meters away from the street lamp, which can be obtained from the question:

2 So: (y+.)

y=6, so x=

So the street lights are xm. long

This is based on similar triangles.

Examples of linear propagation of light are as follows:

1. When a carpenter sharpens wood with a wound, he will always close one eye, which is also based on the principle of linear propagation of light.

2. People designed crosshairs for firearms, which is also an example of the linear propagation of light.

3. When queuing, the coach will see whether the team is standing in line from the front or back, which is obviously the use of the principle of linear propagation of light.

4. The formation of shadows is because light travels along a straight line, and light cannot pass through opaque objects, so the light shines on opaque objects, and there will be an area on the other side of the object that cannot be illuminated, which is the shadow.

5. Determine that the lunar eclipse of the sun, the earth, and the moon are in the same straight line, and the earth is in the middle.

6. Determine that the sun, moon, and earth are in the same straight line during the solar eclipse, and the moon is in the middle.

7. Use a flashlight to illuminate in a darker place at night.

8. Use a plate with a small hole to block between the screen and the object, and the inverted image of the object will be formed on the screen, which we call the small hole imaging.

Linear propagation properties of light:

To represent the propagation of light, we usually use a straight line with an arrow to represent the path and direction of light. Such a straight line is called light. Light travels in a straight line in the same homogeneous medium.

The linear propagation and propagation nature of light has been widely used in the ancient astronomical calendar of China. Our ancestors made the Gui watch and the sundial to measure the length and direction of the sun's shadow to determine the time, the winter solstice, and the summer solstice. A speculum is attached to an astronomical instrument to observe celestial phenomena and measure the position of stars.