"Refraction of Light" Colorful Light PPT Courseware 2

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"Refraction of Light" Colorful Light PPT Courseware 2

[Experience] The phenomenon of refraction of light

Activity 1: Design the experimental device as shown in the figure to allow the laser beam to shoot diagonally into the water from the air with light smoke.

Activity 2: Put a pencil into a cup partially filled with water and observe the pencil in the water.

Activity 3: Place a coin at the bottom of two identical cups, pour water into one of the cups, and observe and compare the differences in the coins in the two cups from above the water.

(1) In activity 1, the direction of the light ray is ________ at the water surface (please fill in "the same" or "deflected"), and the light ray ________ (please fill in the "will" or "won't") enter the water.

(2) In activity 2, the part of the pencil in the water will fold toward ________ (please fill in "up" or "down").

(3) In activity 3, you will find that the coins in the ________(optional "with water" or "without water") cup are shallower.

Tips: (1) deflection, (2) upward, (3) water

pre-study questions

1. What is the refraction of light? What is the content of the law of refraction of light?

2. What are the common light refraction phenomena in daily life?

Explore 1 the phenomenon of refraction of light

Combined with activity 1 in "Experience", think about the following questions:

1. According to the condition that light propagates along a straight line, when light is incident obliquely from one substance to another different substance, the propagation direction usually occurs ______.

Reference answer: Deflection

2. Draw the light path diagram in Activity 1. Following the reflection light path diagram of light, mark the incident ray, refracted ray, normal, incident angle, and refraction angle respectively.

Exploration 2 Explore the laws of refraction of light

1. Experimental design:

(1) When doing experiments, what methods do you have to show the propagation path of light?

Tip: In order to facilitate the observation of the propagation path of light, there are generally three methods: ① Spray smoke in the air ② Drop a little milk or blue ink into the water ③ Place the light screen so that the light is incident close to the light screen.

Reference answers: ① Spray smoke in the air ② Drop a little milk or blue ink into the water ③ Place the light screen so that the light is incident close to the light screen.

(2) How to study the positional relationship between refracted rays, incident rays, and normals in experiments?

Tips: Use a light screen to display the light path, observe the positional relationship between the refracted light, the incident light, and the normal line. Turn the light screen at a certain angle and observe whether there is any refracted light on the light screen. If not, it means that the three are in the same plane.

Reference answer: Turn the light screen at a certain angle and observe whether there is refracted light on the light screen.

Knowledge summary

1. The phenomenon of refraction of light

1. Definition: When light _____ from one substance to another, the propagation direction usually occurs in _____.

2. Several nouns:

(1) Angle: i._____ angle; r._____ angle;

(2) Line: AO._____ light; OB._____ light; NN′.___ line

2. The law of refraction of light

1. Same plane: _____ ray, _____ ray, and ___ line are in the same plane;

2. Divided into two sides: the refracted ray and the incident ray are located on both sides of _____;

3. Angular inequality: The angle of refraction _____ as the angle of incidence increases.

(1) When light is incident from air to other media, the refraction angle _____ the incident angle.

(2) When light is incident obliquely from other media into the air, the refraction angle _____ the incident angle.

4. Vertical incidence: When light is vertically incident from one medium to another medium, the direction of propagation is _____.

3. Refraction phenomenon in life

1. When I was washing my face, I saw the water in the basin _____.

2.The pencil next to the glass looks _____.

3.____________ etc.

Test Points Applying the Laws of Refraction of Light to Draw Drawings

[Typical example] (2012 Shiyan High School Entrance Examination) As shown in the figure, a student observes at point A that the image formed by point light source S in the water is at point B. Please draw the optical path of the light emitted by point S through point A. picture.

[Concise Lecture and Analysis] This question examines the drawing of the refraction laws of light. We can see objects because light enters our eyes. Therefore, the image points B and A we see are on a straight line, connecting AB and the water surface at point O. Then this point is the direction of the light emitted by the point light source S. At the incident point of the water surface, SO is the incident ray and OA is the refracted ray.

Answer: As shown in the picture

[Method Summary] Method of drawing using the refraction laws of light

(1) If the incident (refracted) ray is known, make the refracted (incident) ray.

(2) Given the object and image, make a light path diagram.

1. (2012·Suzhou High School Entrance Examination) Among the following light phenomena, what is formed due to the refraction of light is ()

[Analysis] Choose C. This question examines the phenomenon of refraction of light. Immediate shadows and total solar eclipses are caused by light propagating in straight lines, reflections are caused by the reflection of light, and the "breaking" of branches extending into the water is a phenomenon of light refraction.

2. A beam of light will be refracted when it is incident from the air into the glass. When the incident angle decreases, the refraction angle ()

A. Gradually decreases, but always smaller than the incident angle

B. Gradually increase

C. Gradually decreases, but is always greater than the incident angle

D.remain unchanged

[Analysis] Choose A. This question examines the laws of refraction of light. The key to answering this question is to clarify the refraction phenomenon of light, the relationship between incident light and refracted light, and the incident angle and refraction angle. When light enters glass obliquely from the air, the refracted ray, the incident ray and the normal line are in the same plane, and the refracted ray and the incident ray are separated on both sides of the normal line; the refraction angle is smaller than the incident angle; when the incident angle increases, the refraction angle also increases As the angle of incidence gradually decreases, the angle of refraction gradually decreases, but the angle of refraction is always smaller than the angle of incidence.

3. Regarding the refraction of light, which of the following statements is wrong ()

A. When light enters from one medium to another, the direction of propagation must change.

B. When light is incident obliquely from water into air, the refraction angle is greater than the incident angle.

C. Light is incident from the air into water obliquely. When the incident angle increases, the refraction angle also increases, but it is always smaller than the incident angle.

D. Like the reflection phenomenon of light, the refracted light path is also reversible.

[Analysis] Choose A. This question tests your understanding of the laws of refraction of light. When light is incident obliquely from one medium into another medium, the direction of propagation changes, but when incident perpendicularly, the direction of propagation remains unchanged. When light is incident obliquely from air into water, the refracted light is deflected toward the normal, so the refraction angle is smaller than the incident angle. Angle, the angle of refraction increases as the angle of incidence increases. Since the optical path is reversible in the refraction of light, when light is incident obliquely from water into air, the refraction angle is greater than the incident angle.

Find out where you tend to go wrong?

When a person dives underwater and looks at a big tree on the shore, does the tree he sees appear to be taller or shorter than it actually is?

What kind of phenomenon is this?

[Students’ own answers]

Chopsticks in the water will bend upward and the water will appear shallower. Similarly, the trees on the shore will look shorter than they actually are in the water. This is a phenomenon of light refraction.

[Teacher Comments]

①The principle is correct.

②Error: It is not clear that the propagation of light is from air to water.

【correct answer】

When the light reflected by the big tree shines obliquely towards the water surface, refraction occurs. When the light enters the water and approaches the normal line, it enters the diver's eyes. However, the diver believes that the light always travels in a straight line and looks against the direction of the light due to the illusion. The virtual image is higher than the actual position

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Update Time: 2024-09-29

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