"Lens" Lens and its application PPT teaching courseware

Description

"Lens" Lens and its application PPT teaching courseware

The first part: sorting out new knowledge

1. Type of lens

2. Terminology related to lenses

1. As shown in Figure 5-1-1, whether it is a convex lens or a concave lens, both surfaces of the lens are part of the spherical surface (there are also some lenses where only one surface is part of the spherical surface).

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

3. Optical center: The ______ of a thin lens. The direction of propagation of light passing through the optical center is ________.

3. The effect of lens on light

1. The effect of lens on light

Light path diagram: convex lens

Optical path diagram: concave lens

focus

A convex lens can make light parallel to the main optical axis converge at a point, which is called the focus.

A concave lens can diverge light parallel to the main optical axis. The reverse extension lines of the divergent rays intersect at a point. This point is called the (virtual) focus.

focal length

The distance from the focus to the lens ______, often expressed as ______

[Pointing]The diverging effect of a concave lens on light means that the light emitted from the concave lens is farther away from the main optical axis than the incident light; the converging effect of a convex lens on light means that the light emitted from the convex lens is farther away from the incident light than the incident light. The light is closer to the main optical axis.

2.Three special lights

(1) Three special rays of convex lens (Figure 5-1-2):

①The light rays parallel to the main optical axis pass through the focus after passing through the convex lens.

②The light passing through the focus is parallel to the main optical axis after passing through the convex lens.

③The propagation direction of light passing through the optical center remains unchanged after passing through the convex lens.

(2) Three special rays of concave lens (Figure 5-1-3)

① After the light ray parallel to the main optical axis passes through the concave lens, its reverse extension line passes through the focus.

②The light rays extending through the focus are parallel to the main optical axis after passing through the concave lens.

③The propagation direction of light passing through the optical center remains unchanged after passing through the concave lens.

Lens PPT, Part 2: Application Examples

Type 1 Lens classification

Example 1: Among the lenses shown in Figure 5-1-5, those that are convex lenses are ________, and those that are concave lenses are ________. (fill in alphabetical number)

[ Analysis It is a concave lens.

[Error-prone warning]When judging the type of lens, you cannot simply judge from the convex or concave surface. The key is to compare the thickness relationship between the middle and the edge.

Type 2: Effect of lens on light

Example 2: A large beaker is placed upside down on the table, filled with smoke. Use a flashlight to shine through the bottom of the cup from top to bottom. Adjust the focusing ring of the flashlight so that the light passing through the smoke becomes a cylindrical beam of uniform thickness (Figure 5- 1-6A).

(1) The beaker is filled with smoke, which uses the __________ of light by smoke particles to show the path of light.

(2) Place a convex lens on the bottom of the beaker. The observed phenomenon is as shown in Figure B, which shows that the convex lens has a _________ effect on light.

(3) Place a concave lens on the bottom of the beaker. The observed phenomenon is as shown in Figure C, which shows that the concave lens has a _________ effect on light.

[Analysis] (1) Smoke can show the propagation path of light because smoke particles cause diffuse reflection of light. (2) Comparing Figure B and Figure A, the cylindrical beam converges to a point after passing through the convex lens, which shows that the convex lens has a converging effect on light. (3) Comparing Figure C and Figure A, the cylindrical beam diverges into a wider and wider beam after passing through the concave lens, which shows that the concave lens has a divergent effect on light.

Type 3: Measurement method of focal length of convex lens

Example 3 2018·Yibin As shown in Figure 5-1-6, a convex lens is facing the sun, and a smaller spot appears on the white paper 20 cm below it. This phenomenon reminds us: the convex lens has _____ on light. _function; if the light spot keeps getting smaller when the lens is brought closer to the paper surface for a short distance, it can be judged that the focal length of the lens must be ______ (optional "greater than", "equal to" or "less than") 20 cm.

[ Analysis After being refracted by a convex lens, the light parallel to the main optical axis can converge to the main optical axis to form a smallest and brightest point. This point is the focus of the convex lens. The distance from this point to the optical center of the lens is called the focal length of the lens; according to the meaning of the question It is known that when the lens is brought a short distance closer to the paper surface, the light spot keeps getting smaller. Since the white paper is initially 20 cm away from the convex lens, it means that the focal length of the lens must be less than 20 cm.

Lens PPT, Part 3: Class Feedback

1. The cross-sections of some lenses are shown in Figure 18-1. Among these lenses:

(1) Convex lenses are __________, and their common feature is __________.

(2) Concave lenses are __________, and their common feature is __________.

2. Lenses are made using the ________ phenomenon of light. After passing through the lens, the light parallel to the main optical axis of the convex lens converges at a point on the main optical axis. This point is called the ________ of the lens. The distance from this point to the center of the lens is called ________.

3． As shown in Figure 18-2, Xiao Ming puts a convex lens facing the sun and moves the light screen on the other side of the lens. When the smallest and brightest point appears on the screen, the distance between the two legs of the compass is measured to be 5 cm, then the focal length of the convex lens is approximately ______cm.

4. Draw the propagation direction of the refracted light shown in Figure 18-3 after passing through the lens.

5. Please draw the corresponding lens in the box based on the incident ray and refracted ray in Figure 18-4.

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For more information about the PPT courseware "Lens and its Applications Lenses", please click the Lenses and Their Applications ppt lens ppt tag.

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Update Time: 2024-10-03

This template belongs to Physics courseware People's Education Edition Physics for Grade 8, Volume 1 industry PPT template

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