"Reflection of Light" Light Phenomenon PPT Courseware 11

"Reflection of Light" Light Phenomenon PPT Courseware 11

1. Definition of light reflection:

When light is emitted from one medium to the surface of another medium, the propagation phenomenon in which part of the light returns to the original medium is called light reflection.

Light will be reflected when it hits the surface of any object. What do you want to know about the reflection of light?

What are the rules for reflected light and incident light? In what direction does the reflected light go out? Is there any relationship between the reflection angle and the incident angle? …

2. Exploration: The rules of light reflection

Ask students to discuss and guess in what direction the reflected light will emit based on the direction of the incident light shown in the picture?

Explore the laws of light reflection

Noun introduction:

1. Incident light, reflected light

2. Incident point O: The projection point of the incident light on the mirror

3. Normal line ON: the straight line passing through the incident point O and perpendicular to the mirror surface

4. Incident angle: the angle between the incident light and the normal

5. Reflection angle: the angle between the reflected light and the normal line

Content and steps

(1) Let the incident light be projected onto the plane mirror along the light screen and observe the direction of the reflected light.

(2) Study the mutual positional relationship between reflected light, normal line and incident light.

(3) Study the relationship between the reflection angle and the incident angle.

law of reflection of light

1. Reflected rays, incident rays and normals are all in the same plane;

2. The reflected light and the incident light are separated on both sides of the normal;

3. The angle of reflection is equal to the angle of incidence.

Shorthand: "Three lines are coplanar, the normal line is in the middle, and the two angles are equal."

Some explanations on the law of light reflection:

1. When the incident angle increases (or decreases), the reflection angle also increases (or decreases)

2. "The angle of reflection is equal to the angle of incidence" can never be said to be "the angle of incidence is equal to the angle of reflection". Because there is incident light first, and then there is reflected light, and the reflection angle comes after the incident angle.

3. When the incident light is vertically incident on the interface of the medium. Then "the incident light, the normal, and the reflected light" combine to form a straight line. At this time, the incident angle is equal to 0 degrees, and the reflection angle is also equal to 0 degrees.

4. The normal line is equivalent to the angle bisector of the angle between the incident light and the reflected light. The normal line is always perpendicular to the interface.

Specular reflection: The reflective surface is flat and smooth; when light is incident in parallel, it will be reflected parallelly and the light will be concentrated.

Diffuse reflection: The reflective surface is rough and uneven; when light is incident in parallel, the reflected light is scattered in all directions.

White paper and a plane mirror placed in the sun, the light reflected by the plane mirror can only be seen at a certain angle. And the white paper can be seen from any angle. We can see clearly objects that do not emit light themselves because of diffuse reflection.

Typical example 1

1. Which of the following statements violates the law of reflection of light ( )

A. As the incident angle increases α, the angle between the reflected light and the incident light also increases α

B． Incident light rays move closer to the normal, and reflected rays also move closer to the normal.

C. The angle of incidence is 0°C, and the angle of reflection is also 0°C.

D. Even if the incident angle is 0°C, the reflected ray is still in the same plane as the incident ray

Warm reminder: As the incident angle increases by α, the reflection angle also increases by α, and the angle between the reflected light and the incident light increases by 2α.

Practice questions

1. When light strikes a plane mirror at an angle of 30° with the mirror surface (as shown below), what is the incident angle? Try to draw the reflected ray and mark the angle of incidence and angle of reflection.

2. Regarding the applicable scope of the law of reflection of light, the correct statement is ( )

A. The law of reflection of light only applies to specular reflection B. Diffuse reflection does not obey the laws of reflection of light

C. The law of reflection of light does not apply to vertical illumination D. The law of light reflection applies to all light reflection phenomena

3. A light ray is reflected on the surface of an object, and the reflected light ray is perpendicular to the incident light ray, then ( )

A. The angle of incidence is 45° B. The angle of incidence is 90°

C. The reflection angle is 35° D. Incident light ray perpendicular to object surface

4. A can see B’s eyes from a mirror, then B can see from this mirror ( )

A. You must see A’s eyes

B． You must not be able to see A’s eyes

C. You may or may not be able to see A’s eyes

Small scale chopper

1. (09 Guiyang) As shown in the picture, many buildings use glass for exterior wall decoration. This not only beautifies the city, but also causes light pollution. The main reason for this pollution is that the sunlight produces _____ on the glass surface. reflection.

2. Which of the following understandings about normals is wrong ( )

A. The normal is a ray perpendicular to the interface

B． The normal is not a light, it is a geometric straight line made to study the rules of light reflection.

C. The normal passes through the point of incidence and is perpendicular to the interface

D. The normal is always the straight angle bisecting the reflected ray and the incident ray

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