"Scientific Exploration: Convex Lens Imaging" Colorful Light PPT Courseware 2

"Scientific Exploration: Convex Lens Imaging" Colorful Light PPT Courseware 2

【Experience】Convex Lens

Activity: Prepare a reading lens and a myopia lens

Activity 1: Observe the shapes of presbyopic lenses and myopia lenses.

Activity 2: Use presbyopic lenses and myopia lenses to observe nearby objects (such as text in a book).

Activity 3: Put the presbyopic lenses and myopia lenses under the sun respectively, adjust their distance from the ground, and observe whether there are any bright spots on the ground.

(1) In activity 1, the shape of the presbyopia lens is _________ in the center and _________ on the edge. The shape of the lens for myopia is _________ in the center and ________ on the edge.

(2) In activity 2, when you are close to the book, the words you see through your reading lenses are ________, and the words you see through your myopia lenses are ________.

(3) In Activity 3, the sunlight shines through the reading glasses on the ground ________ (optional "yes" or "no") bright spots on the ground. ________ (optional "yes" or "no") bright spots on the ground through myopia glasses.

Tips: (1) Thicker, thinner, thinner, thicker (2) Enlarged, reduced (3) Yes or no

pre-study questions

1. What are the characteristics of the shape of a convex lens?

2. What effect does a convex lens have on light?

3. What are the optical center, main optical axis, focus and focal length of a convex lens?

Explore convex lenses

Combine the activities and previews in "Experience" and think about the following questions:

1. Analyze the picture above. The shape of the convex lens is __________, and the shape of the concave lens is __________. Therefore, the presbyopia lens is a __________ lens and the myopia lens is a __________ lens.

Tip: Analyzing the shapes of convex lenses and concave lenses, we know that the shape of convex lenses is thicker in the center and thinner at the edges. The shape of a concave lens is thinner in the center and thicker at the edges. Myopia lenses conform to the shape characteristics of concave lenses, and presbyopia lenses conform to the shape characteristics of convex lenses.

Reference answer: thicker in the center and thinner at the edges; thinner at the center and thicker at the edges; convex and concave;

2. Combine activity 3 and the following pictures to observe the light refracted by parallel light through convex lens and concave lens. You will know that convex lens has ______ effect on light and concave lens has ______ effect on light.

Tip: After the sunlight passes through the convex lens, it forms a small bright spot, which shows that the convex lens has a converging effect on the light. Sunlight spreads outward after passing through a concave lens, indicating that the concave lens has a divergent effect on light.

Reference answer: convergence divergence

Knowledge summary

1. Lens

1. Production principle: Made using the _________ principle.

2. Classification:

(1) Convex lens: The center is ___ and the edges are ___.

(2) Concave lens: The center is ___ and the edges are ___.

3. Effect on light:

(1) Convex lens: It has _____ effect on light.

(2) Concave lens: It has _____ effect on light.

2. Focus and focal length of the lens

1. Optical center (O):

(1)Definition: _____ of lens.

(2) Characteristics: The propagation direction of light passing through the optical center is _____.

2. Principal optical axis: a straight line passing through two spherical surfaces _____.

3. Focus (F): The point formed by light parallel to the main optical axis passing through the convex lens _____. convex

There is a focal point on each side of the mirror.

4. Focal length (f): The distance from the focus to _____.

Test points: Special light rays from lenses

[Typical example] (2012 Tai'an High School Entrance Examination) As shown in the figure, of the two rays emitted from the light source S, one is parallel to the main optical axis of the convex lens, and the other passes through the focus of the convex lens. Please draw these two rays passing through the convex lens. the refracted rays.

[Idea Guide] Determine the characteristics of the two incident rays: parallel to the main optical axis and passing through the focus on one side, and draw a light path diagram based on the characteristics of the refracted ray.

[Intensive Lecture and Analysis] This question examines three special rays of convex lens. The incident light ray parallel to the main optical axis, after being refracted by the convex lens, passes through the focus; the incident light ray passing through the focus, after being refracted by the convex lens, becomes parallel to the main optical axis. A convex lens has three special incident light rays: those passing through the focus, those passing parallel to the main optical axis, and those passing through the optical center; the propagation direction of the incident light passing through the optical center remains unchanged after being refracted by the convex lens.

Answer: As shown in the picture

1. As shown in the figure is a schematic diagram of several optical equipment, among which the ones that can diffuse light are ()

[Analysis] Choose D. This question examines the effect of concave lenses on light. Convex lenses converge light, and concave lenses diverge light. The convex lens is thick in the middle and thin at the edges, so A, B, and C are convex lenses. The concave lens is thin in the middle and thick at the edges, so D is a concave lens. So choose D.

2. A light-condensing bead used in a flashlight is as shown in the figure. Its front end is equivalent to a convex lens made of glass. In order to make the light emitted by the filament turn into parallel light after passing through the convex lens, the filament should be placed in ()

A. At the focus B. Within the focus

C.Out of focus D.Anywhere

[Analysis] Choose A. This question uses light-concentrating beads in daily life as the research object, applies physical knowledge to real life, and stimulates students' interest in learning. According to the light converging effect of the convex lens and the reversibility of the optical path, it can be seen that the light emitted from the focus will be parallel to the main optical axis after being refracted by the convex lens, so choose A.

3. The optical path diagram of light passing through the lens is as shown in the figure. The correct one is ()

[Analysis] Choose B. This question examines the effect of lenses on light. Convex lenses have a converging effect on light. Lenses A and B are convex lenses, so A is wrong and B is correct. Concave lenses have a divergent effect on light. Lenses in items C and D are concave lenses, so C and D are wrong.

4. (2012·Heze High School Entrance Examination) When traveling in the forest, please do not throw away drink bottles at will. Because after water enters the beverage bottle, it is equivalent to a ________ mirror, which has a ________ effect on sunlight and can easily cause a fire.

[Analysis] This question examines the converging effect of convex lenses on light. After water enters the beverage bottle, the water in the bottle is thick in the middle and thin at the edges, which is equivalent to a convex lens. It has a converging effect on light and can easily ignite dead leaves and cause fires.

Answer: convexity, convergence

Find out where you tend to go wrong?

Draw the refracted ray corresponding to the incident ray in the figure below.

[Students’ own answers]

[Teacher Comments]

Errors: ① The direction of the light is wrong; ② The refraction situation is wrong: the light incident through the focal point of the convex lens, after being converged by the lens, is emitted parallel to the main optical axis.

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