"Lens" Lens and its applications PPT courseware 6

Description

"Lens" Lens and its applications PPT courseware 6

Activity 1: Classification of lenses

Convex lens:

Thick in the middle, thin at the edges

concave lens:

Thin in the middle, thick at the edges

The main optical axis and optical center of the lens:

The straight line on the lens passing through the two spherical centers O1O2 is called the principal optical axis.

There is a point O at the center of the lens, called the optical center

Activity 2: Observe convex and concave lenses

How to do it: Put the lens close to the book and observe the words in the textbook.

in conclusion

Through a convex lens, the image of the object seen is (enlarged/reduced), (upright/inverted).

Through a concave lens, the image of an object seen is (enlarged/reduced), (upright/inverted).

Activity 3: Explore the effect of lenses on light

Exploration experiment

(1) Place a convex lens facing a beam of parallel light, place a piece of white paper on the other side of the lens, move it back and forth, and observe any changes?

(2) When using a concave lens, can I get a very small and bright spot on the paper? What does this mean?

Experimental results

Convex lenses have a converging effect on light, so convex lenses are also called converging lenses.

Concave lenses have a divergent effect on light, so concave lenses are also called divergent lenses.

Discussion and exchange

How many simple methods do you have to identify whether a certain lens is a convex lens or a concave lens?

Method 1: "Touch". It is distinguished by comparing the thickness of the center and edge of the lens. (Note: To prevent the mirror from being worn or stained, wrap the lens with soft tissue paper before touching it with your hands)

Method 2: "Look". Observe nearby objects through a lens and discern whether they appear enlarged or reduced.

Method three: "Photo". A lens is used to determine whether parallel light converges or diverges.

Activity 4: Use your hands and brain to learn physics

1. Try one or two convex lenses. How can you estimate the focal length of a convex lens?

Method (1): Hold a convex lens facing the sun, let the light shine through the convex lens onto the white paper, move the convex lens to make the light spot very small and bright, use a scale to measure the distance from the light spot to the convex lens.

Method (2): On the optical bench, let the light from the light source shine on the convex lens, move the light source and the light screen, find a small and bright spot on the light screen, and use a scale to measure the distance between the light screen and the convex lens.

2. If you want to use a convex lens to turn the light emitted by a small bulb into parallel light, where should the small bulb be placed on the convex lens? Try it. What principles did you actually use to solve this problem? Let’s take a guess first.

Answer: At the focus position. Because light is refracted through the surfaces on both sides of the convex lens, the refracted light path is reversible. The light parallel to the main optical axis must be converged to the focus through the convex lens. Then, the light emitted from the focus will come out parallel to the main optical axis through the convex lens.

three special rays

1. The propagation direction of light passing through the optical center does not change.

2. The light rays parallel to the main optical axis pass through the focus after being refracted by the convex lens, and diverge after being refracted by the concave lens. The reverse extension line of the divergent light passes through the virtual focus.

3. The light that passes through the focus of the convex lens is refracted and emitted parallel to the main optical axis.

What did I gain?

Understand convex lenses and concave lenses; know how to distinguish convex lenses and concave lenses

Understand the effects of convex lenses and concave lenses on light and how to measure the focal length of convex lenses

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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: 2024-07-11

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

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