First, the concept of physical light reflection in junior high school
The concept of light reflection law: the phenomenon that light changes its propagation direction at the interface between two substances and returns to the original substance is called light reflection. For humans, the greatest reflection of light occurs on the moon. As we all know, the moon itself doesn't shine, it just reflects sunlight. So the reflection of light is everywhere and happens around people.
Second, the reflection classification of physical light in junior high school
1) Specular reflection: When parallel light shines on a smooth surface, the reflected light is also parallel, which is called specular reflection.
2) Diffuse reflection: parallel light shines on uneven surface, and reflected light shines in all directions. This reflection is called diffuse reflection.
3) Physical phenomena of specular reflection and diffuse reflection: objects with smooth surfaces are easy to form specular reflection and harsh glare of light, but they cannot be seen clearly. Usually, the shape and existence of an object can be distinguished by the diffusion of light. Because of the diffusion of light caused by dust in the air, objects can be seen temporarily after sunset. Whether it is specular reflection or diffuse reflection, we must abide by the law of reflection.
Third, the reflection law of junior high school physical light (key):
1. The reflection angle is equal to the incident angle, and the angle between the incident light and the plane is equal to the angle between the reflected light and the plane.
2. The reflected light and the incident light are on both sides of the normal, and both are on the same plane.
3. In the phenomenon of light reflection, the light path is reversible. Fourth, according to the reflection law of light, make a light path diagram (common knowledge points):
First find the incident point, and the normal perpendicular to the interface passes through the incident point, then the bisector of the included angle between the reflected light and the incident light is the normal. If the reflected light corresponding to the incident light is determined, the incident angle and the plane where the reflected light is located are determined by the incident light and the normal line, and then the reflected light is determined according to the characteristics that the reflected light is located on the other side of the normal line and the reflected angle is equal to the incident angle in the reflection law of light.
Five, the four characteristics of junior high school physical light reflection (difficulties):
The normal of 1 * * * The plane is the straight line where the angular bisector of reflected light and incident light is located.
2. The sum of the included angle and incident angle between the incident light and the reflecting surface on the opposite side is 90.
3. The equiangular reflection angle is equal to the incident angle. The reflection angle increases with the increase of incident angle and decreases with the decrease of incident angle.
4. Reversible optical path is reversible.
Six, junior high school physical light reflection exercises (including experimental questions):
1, junior high school physical light reflection multiple-choice questions
1. The TV remote controller can emit an invisible light, called infrared, which is used to transmit information and realize remote control of the TV. Sometimes you can control the TV without pointing the remote control at the TV control window. This is the use of () A. The straight-line propagation of light B. The curved propagation of light C. The reflection of light D. The reversibility of light.
2. Light pollution has become a concern in 2 1 century. According to the measurement, the white and smooth indoor walls can reflect 80% of the sunlight shining on the walls, so reading and studying in such a dazzling environment for a long time will be very uncomfortable. If the wall is made into an uneven surface, one of its functions is to make the sunlight shining on the wall become scattered light, thus achieving the purpose of protecting eyesight. This uses () A. Linear propagation B. Diffuse reflection C. Specular reflection D. Reflection of light.
3. As shown in figure 1, if a beam of light is aimed at a plane mirror, then the incident angle and reflection angle of this beam of light are () a.40 40 b.40 50 c.50 40 d.50 50 4. The following statement is incorrect ().
A. The light shines vertically on the plane mirror with an incident angle of 90.
B. diffuse reflection also obeys the law of reflection.
C If the included angle between the reflected light and the incident light is 120, the incident angle is 60.
D It takes about 500s for the light from the sun to reach the earth, so the distance from the sun to the earth is about 1.5× 108km.
5. Xiao Cong sees Xiao Cong's eyes in some way, so Xiao Ming () A. Must see Xiao Cong's eyes B. Must not see Xiao Cong's eyes C. Must not see Xiao Cong's eyes D. Must see Xiao Cong's whole body 2. Reflection of physical light in junior high school
1. I dropped my wallet under the sofa. Without a flashlight, Xiao Ming found his wallet with the help of the light reflected by a flat mirror. Reflected light and incident light have been marked in the figure. Please mark the plane mirror in the picture and draw the normal.
2. (junior high school physical light reflection experiment) As shown in the figure, it is an experiment that Chen Tao explores the law of light reflection. He did the following:
(1) As shown in figure 1 A, let a beam of light stick to the cardboard at a certain angle and emit in the other direction, change the incident direction of the beam, so that ∠i decreases, then ∠r decreases, so ∠ i increases and ∠r increases.
(2) As shown in figure 1B, fold the half plate NOF forward or backward. At this time, you can't see _ _ _ _ _ _ _-on the NOF, which means that.
3, junior high school physical light reflection experiment _ _ _ _ _. Reference answer: 1, multiple-choice question:/kloc-0 1.c2.b3.d4.a5.a
2. Application problem: 1. (as shown)
2.( 1) Shadow formation: light travels in a straight line; (2) reflection in water: reflection of light VII. Physical phenomena of light reflection in life;
1, the mirror we look at every day.
2. A convex mirror placed at the intersection.
3. Car rearview mirror.
We can see objects, and objects reflect light into our eyes. 5. Solar heaters (solar cookers)
6.periscope.
7. reflecting telescope.
Shanghai senior high school entrance examination combines physical chemistry into one, with 90 points in physics. Refraction of light is more difficult than straight-line propagation and reflection of light. Students need to master the related knowledge points of light refraction drawing problems and experimental problems. Only the new curriculum provides the following courses for junior high school subjects:
The above characteristic courses are equipped with junior high school textbooks, and the teaching forms are divided into face-to-face lectures and online courses. The types of face-to-face courses are different, such as 1 to 1, 1 to 3, 15, 30-person classes, etc. The teaching hours in different districts of Shanghai are also different. Please call the official website hotline at 4008-770-970 for details of the course.