"Lens and Vision" PPT download

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"Lens and Vision" PPT download

Part 1: Thoughts before class

1. How to roughly measure the focal length of a convex lens?

Facing the convex lens to the sun, use a piece of white paper as a light screen on the other side of the convex lens so that the convergence point of the light appears on the light screen. Use a scale to measure the distance from the center of the lens to the convergence point, which is the focal length f.

2. Do you know what else a convex lens can do besides focusing light?

Explore the imaging rules of convex lenses

1. Experimental instruments:

2. Experimental steps

⑴ Place the candle, convex lens, and light screen on the light bench from left to right in order, and make the centers of the three at roughly the same height.

⑵ Light the candle and place it as far away from the convex lens as possible. Then move the light screen so that an inverted, reduced and clear image of the candle flame appears on the light screen and fill in the observation results in the table.

⑶ Move the candle close to the convex lens and repeat the above steps until an inverted magnified, equal-sized and clear image of the candle flame appears on the light screen and fill in the observation results in the table.

⑷ Then bring the candle close to the lens to u

Lens and Vision PPT, Part 2: Discussion

1. What do the images formed on the light screen have in common? inverted real image

2. Which point is the dividing line between reducing and enlarging the real image?

At twice the focal length (two focal lengths)

3. Which point is the dividing line between real and virtual images?

At twice the focal length (one focal length divides the virtual and the real)

4. When the convex lens is fixed, the candle approaches the focus from a distance. In order to find the image, how should the light screen move? How does the size of the image change?

When the light screen moves away from the convex lens, the image distance increases, and the image also increases.

(Things that advance seem to recede, and the image becomes larger) (Things that recede seem to advance, and the image becomes smaller)

Lens and vision PPT, part three: a small test of your skills

1. What cannot be formed by a convex lens ( )

A． Upright magnified virtual image B. Inverted enlarged real image

C． A real image of the same size as an inversion D. upright enlarged real image

2. The virtual image formed by an object passing through a convex lens must be ( )

A． Upright, magnified B. upright, reduced

C． Inversion, magnification D. handstand, shrink

3. In the experiment of "Studying Convex Lens Imaging": When the focal length f of the convex lens is 10 cm, and the candle is 14 cm away from the lens on the left side of the convex lens, the light screen on the right side can be obtained ( )

A. Inverted, equal-sized real image B. Inverted, reduced real image

C. Inverted, enlarged real image D. Upright, enlarged virtual image

Lens and Vision PPT, Part 4: Expansion

Discuss and resolve the following issues

1. What are the methods for measuring the focal length of a convex lens?

① Place the convex lens toward the sunlight, and use a piece of white paper as a light screen on the other side of the convex lens so that the convergence point of the light appears on the light screen. Use a ruler to measure the distance from the center of the lens to the convergence point, which is the focal length f.

② Do the imaging experiment on the optical bench. Place a candle flame and a light screen on both sides of the lens. Move the positions of the candle flame and the light screen until the image presented on the light screen is clear and equal in size. Then use a scale to measure the distance from the center of the lens to the candle. The distance of the flame is u, then f=u/2.

2.How to distinguish convex lens from concave lens?

① See with your eyes and touch with your hands (distinguish from appearance): The one with a thick middle and thin edges is a convex lens, and the one with a thin middle and thick edges is a concave lens;

② Face one side of the lens to the sun, put a piece of white paper on the other side, and move the lens. If you find a bright spot converging on the white paper, it is a convex lens. If there is no bright spot, it is a concave lens;

③ Use the lens as a magnifying glass. If you can see the magnified object, it is a convex lens. If you cannot see the magnified object, it is a concave lens.

3. When doing the convex lens imaging experiment, the image cannot be found on the light screen. What are the possible reasons?

①The centers of the candle flame, lens, and light screen are not adjusted to the same height;

②The object is placed at or within the focus.

Keywords: Zhejiang Education Edition seventh grade science PPT courseware for the second volume free download, lens and vision PPT download, .PPT format;

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Update Time: 2024-07-04

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