The reflected light and the incident light are on the same plane as the normal;The reflected light and the incident light are separated on both sides of the normal;Reflection anglebe equal toAngle of incidence。It can be summarized as: "three lines are coplanar, two lines live apart, and two angles are equal".Light is reversible.In the reflection of light, the light path is equal[1]。
(1) When light is reflected, reflect lightIncident light, normals are in the same plane.(in the same plane)
(2) When light is reflected,Reflected light, separation of incident lightnormalboth sides.
(3) When light is reflected,Reflection angleEqual to the angle of incidence.(Equal angles)
Conclusion: When light shines on the surface of an object, part of it is reflected back by the surface of the object. This phenomenon is calledReflection of light。
exceptional case
In case of vertical incidence, the incidence angle and the reflection angle are all zero degrees, and the normal line, the incident light and the reflected light are in one line.[2]
classification
Announce
edit
Two kinds of reflection: specular reflection and diffuse reflection
Illustration
oneSpecular reflection: The parallel ray is reflected from the interface and emitted in parallel in a certain direction. It can only be received in a certain directionReflected light(The reflecting surface is a smooth plane).
two.diffuse reflection: The directional light reflects through the interface and then goes to differentDirectional reflectionGoing out means that the reflected light can be received in different directions (the reflecting surface is a rough plane or surface).
However, both specular reflection and diffuse reflection follow the reflection law of light;Diffuse reflection is only due to the fact that the reflecting surface is not parallel to each other and forms irregular reflection. It means that there are some arcs or sharp lines on the uneven surface. Suppose a ray hits the surface and its tangent line is taken as the plane as the reflection ray, so there are many small "mirrors" to form diffuse reflection.
Note: the light path is reversible in the reflection of light[3]。
Deep understanding of laws
Announce
edit
It can be summarized as: "three lines are coplanar, two lines live apart, and two angles are equal".Light is reversible.In the phenomenon of light reflection, the light path is equal.
experimental verification
Announce
edit
Experiment of light reflection law
Experiment purpose: Find out the law of light reflection.
The reflection of light is studied in the experiment, in which the plane mirror with strong light reflection ability is selected as the reflecting surface, and white cardboard and white paper are used to show the path of light beam propagation.
(1) As shown in Figure 1, first make E and F become the same plane, so that the incident light hits the O point on the mirror along the cardboard, and observe the direction of the light reflected from the mirror.
Figure 1, Figure 2, Figure 3
(2) Change the direction of the incident light and observe how the direction of the reflected light changes.
(3) Fold sheet F forward or backward as shown in Figure 2.
For experimental research on the relationship between the reflection angle and the incidence angle, the experimental device shown in Figure 3 can be used.
① A piece of 16 K white paper is fixed on the horizontal desktop with thumbtacks or transparent tape, and a straight line ON is drawn in the middle of the white paper as the normal;Draw several straight lines OA and OA with different angles on the side of ONone、OAtwo。
② Let the light emitted from the paper seam in front of the flashlight run along OA and OA respectivelyone、OAtwoShoot at the mirror and observe the reflected light.
③ Use a big needle to pierce holes B and B at each reflected light positionone、Btwo。Draw a straight line with a scale to connect OB, OB1 and OB2.
④ Then measure the reflection angle (r) and incidence angle (i) with a protractor, and record the values for comparison.
⑤ Make the light follow OB and OB respectivelyone、OBtwoShoot at the mirror and observe the direction of each reflected light.
Analysis and demonstration：
(1) In steps 1 and 2 above, it can be seen that when E and F are in the same plane, there is reflection light, and the reflection light changes with the change of the incident light.
(2) Fold the sheet F forward or backward as per step 3, and the reflected light will not be observed.
(3) It can be seen from ① - ④ of step 4 that the reflection angle is equal to the incident angle.
(4) It can be seen from ⑤ of step 4 that the reflection path is reversible.
explain: (1) The reflection law of light can be summarized as "twelve words, three lines, coplanar, two lines living apart, two angles equal".
(2) The third reflection angle of the reflection law is equal to the incidence angle. It cannot be said that the incidence angle is equal to the reflection angle, because there is incidence before reflection;The incidence is before the reflection;Incidence is cause, reflection is effect.
(3) In reflection, the light path is reversible.
Scope of application
Announce
edit
The reflection law of light applies to all light reflection phenomena, whetherSpecular reflectionstilldiffuse reflection, both apply.The reflection law of light is not only applicable to vertical irradiation, but also to oblique irradiation.
Development History
Announce
edit
Presenter
The reflection law of light was established by French civil engineering and physicistfresnel(1788-1827).He discovered the relationship between reflection/refraction and viewpoint angle.Therefore, the reflection of light is also calledFresnel reflection。
If you stand by the lake and look down at the water at your feet, you will find that the water is transparent and the reflection is not particularly strong;If you look at the lake in the distance, you will find that the water is not transparent, but the reflection is very strong.This is the Fresnel effect.
In the real world, except for metals, other substances have different degrees of "Fresnel effect".
application area
Announce
edit
(1) The reflection in the water.(belongs to reflection)
(2) Rear view mirror on the vehicle（Reflection of light）
A bicycle reflector is made by using the reflection law of a right angle plane mirror.At night, when the light from the car lamp shines on the reflector of the bicycle, it will be reflected by two reflective surfaces at right angles to each other on the bicycle, and the reflected light will reverse into the driver's eyes in the direction parallel to the incident light, so that the driver can easily find the cyclist, which is conducive to driving safety at night.
