Find the answer to the eighth grade physics problem!

1. Light travels fastest in vacuum, and 3× 108 is obtained.

M/s. "Looking at the sky from a well, I can see very little" is due to the straight-line propagation of light.

2. A classmate's height is 1.6m, and he stands in front of a flat mirror of 1.2m, so his image height in the mirror is 1.6m, and the distance between him and the image is 2.4m ..

3. China has an ancient book, Huainan Wanbi Book, which records a passage: "Take a big mirror and put a basin under it, and you can see your neighbor." This is to observe the surrounding scenery by using the principle of plane mirror imaging; You can see some objects that don't emit light from different directions because of the diffuse reflection of light on the surface of the object, while the "reflection" of the blackboard is due to the specular reflection of light on the polished blackboard surface. 4. If the incident light is perpendicular to the plane mirror, the incident angle is 0; If the direction of the incident light is unchanged, rotate the plane mirror 10 around the incident point, and the included angle between the reflected light and the incident light is 20.

5. As shown in figure 1, it is the optical path diagram of reflection and refraction when light obliquely enters the glass from the air. If ∠3=∠6 is known, the incident light is CO, the interface is EF, and the right side of the interface is glass.

6. When checking eyesight, the distance between people and the eye chart should be 5m. Now use a flat mirror because the room is too small. The distance from the eye chart to the plane mirror is 3m, so the distance from the person to the mirror should be 2 m. If the full length of the eye chart is 0.8 m, the image length of the eye chart in the mirror is 0.8m.. ..

7. A classmate stood on the riverbank and looked at the water in the river, which was shallower than the actual water. Divers look at the trees on the river bank in the water. These trees are higher than the actual water. (Fill in "shallow" or "high")

9. The human eye is a "magic camera". In Figure 3, _ _ _ _ _ _ is equivalent to the lens of a camera, and _ _ _ _ _ _ _ (fill in "convergence" or "divergence") light can be converged on the retina, which is equivalent to the _ _ _ film of the camera. 10. To make the object stand upright and enlarge it through the convex lens, put the object at the f of the convex lens; The object is turned into an inverted enlarged image through the convex lens,

The object should be placed between f and 2f of the convex lens. Figure 3

Between; If the object is inverted and shrunk by the convex lens, it is necessary to put the object outside the convex lens.

1 1. "Three primary colors" refer to red, green and blue. The color of transparent body is determined by the color of its reflected light.

12. The words in the book are magnified by water drops, which are equivalent to a magnifying glass.

13. The difference between a microscope and a telescope: (1) A telescope is a "hyperopic eye", and its objective lens has a long focal length, which can magnify distant objects.

Body.

(2) Microscope is nearsighted, and the focal length of the objective lens is short, which can only magnify near objects.

14. At night, a person gradually approaches a street lamp and then gradually moves away from it. The change of this person's shadow length is a.

A.it gets shorter first, then longer. B. It becomes longer first and then shorter. C.it's getting shorter. D. it gets longer and longer. 15. The following phenomena do not belong to the straight-line propagation of light. B.

A. hand shadow game B. phantom C. pinhole imaging D. sunlight penetrating into forest 16. The focal length of the convex lens is 10cm. If the lit candle is placed 40 cm in front of the convex lens, the image formed by the candle flame passing through the convex lens is A.

A. real image reduced by handstand B. real image enlarged by handstand C. real image with the same size as handstand D. virtual image enlarged vertically 17. Xiao Ming sees the mirror image indicating the electronic clock from the plane mirror as shown in Figure 4, and the time at this time should be ca.21:10b.10: 265438+.

18. In the absence of any other light, the green light from the stage spotlight is covered with a white coat.

On the actress wearing a red skirt, the audience saw that her dress color was D.

A. the whole body is green. The coat is green and the skirt is red.