"Exploring the Imaging Laws of Convex Lenses" Light and Eyes PPT Courseware

Description

"Exploring the Imaging Laws of Convex Lenses" Light and Eyes PPT Courseware

learning target

1. Understand the rules of imaging by convex lenses through experimental exploration

2. Know how a magnifying glass works

3. Preliminarily learn to formulate experimental plans and select equipment required for experiments based on the purpose of inquiry.

4. Through experiments, develop experimental operation capabilities and preliminary analysis capabilities for experimental phenomena and data.

Core test point: "Exploring the rules of imaging by convex lenses" experiment.

Preview before class

1. The object distance is the distance from the object to the convex lens _____, represented by the letter _____. The image distance is the distance from the image to the convex lens _____, represented by the letter _____.

2. The real image is the image of _____ presented on the light screen, which is formed by the convergence of _____. The virtual image is an image of _____ presented on the light screen. It is not formed by the convergence of _____, but by the intersection of __________.

3. The imaging rules of a convex lens: when an object is beyond twice the focal length, it forms an inverted, _____ real image; when the object is exactly at twice the focal length, it forms an inverted, _____ real image; when an object is between twice the focal length and one time the focal length, it forms an inverted, _____ real image. It forms an inverted, _____ real image; an object within one focal length forms a _____, enlarged _____ image.

4. When the object is less than one focal length away from the magnifying glass, a ________ image can be seen through the magnifying glass, and the image and the object are on the _____ side of the magnifying glass; the image formed by the magnifying glass is not the actual light rays converging, but the image formed by the person. What is seen with the eye against the emitted ray is called a _____ image.

Lectures in class

Knowledge point 1. Experimental research on convex lens imaging

(1) Three important physical quantities involved in convex lens imaging: object distance, image distance, and focal length

The distance from the object to the center of the convex lens is represented by the letter M, as shown in the figure below. For example, u=35 cm means that the object is 35 cm from the center of the convex lens; the distance from the image formed by the object through the convex lens to the center of the convex lens is called the image distance, as follows As shown in Figure A, it is represented by the letter u. For example, v=16 cm means that the image formed by the object through the convex lens is 16 cm away from the center of the convex lens. The distance from the focus to the optical center of the convex lens is called the focal length, represented by the letter f, as shown in Figure B below. , for example, f=10 cm means that the focal length of a certain convex lens is equal to 10 cm.

(2) Experimental research on convex lens imaging

① Experimental equipment:

Light benches, convex lenses, candles, light screens, matches, etc.

②Experimental steps:

a. Place candles, lenses and light screens on the light bench from left to right.

b. Adjust the centers of the entire candle flame, lens, and light screen to approximately the same height.

c. Conduct the experiment (pay attention to adjusting the object distance and image distance to make the image of the candle flame the clearest).

③The reason why the image cannot be obtained on the light screen:

a. The object is in focus and cannot be imaged;

b. The object becomes a virtual image within one focal length;

c. The flame center of the candle, the light center of the convex lens, and the center of the light screen are not at the same height;

d. The candle is beyond one focal length, but too close to the focus, the image is too far, and the optical bench is not long enough.

Memory tips: One focus divides virtual and real images (that is, objects within one focal length form a virtual image, and objects beyond one focal length form a real image);

Difocal size (that is, if the object distance is less than twice the focal length, it will form an enlarged image, except for the focal point; if the object distance is greater than twice the focal length, it will form a reduced image);

The closer the object is to the focus, the farther the image is from the focus, and the larger the image is.

The object is far away and the image is small (the farther the object is from the focus, the closer the image is to the focus, and the smaller the image is);

The virtual image is upright on the same side (when a virtual image is formed, the image and the object are on the same side of the convex lens, and the image is upright);

The real image is inverted on opposite sides (when forming a real image, the image and the object are on opposite sides of the convex lens, and it looks like it is upside down).

Notice:

a. The focus F is the dividing point between the real image and the virtual image of the object;

b.Twice the focal length is the dividing point between the enlarged image and the reduced image of the object;

c. When forming a real image, the closer the object is to the focus, the farther the image is from the focus, and the larger the image becomes; the further the object is away from the focus, the closer the image is to the focus, and the smaller the image becomes.

d. Getting bigger and smaller: refers to the comparison of the later image with the original image; enlargement and reduction: refers to the comparison of the image of the object with the object itself.

[Example 1] (2014·Suining) In the activity of exploring "Convex Lens Imaging Rules and Applications", Yangyang chose a convex lens with an unknown focal length.

(1) Install the convex lens on the optical bench, use parallel light as the light source, move the light screen, and obtain the smallest and brightest spot on the light screen, as shown in Figure A, then the focal length of the convex lens is ____cm.

(2) Install the candle, convex lens, and light screen on the light bench in sequence, and adjust the centers of the candle flame, convex lens, and light screen so that they are roughly on ____ to prepare for the experimental investigation.

(3) In the situation shown in Figure B, keep the positions of the light screen and the convex lens unchanged, and move the candle a certain distance to the left. In order to obtain a clear image on the light screen again, a focal length should be installed near the left side of the convex lens. appropriate_____.

A. Convex lens B. concave lens

(4) If the position of the convex lens remains unchanged and the candle is moved to 35cm on the ruler, an inverted _____ real image will be obtained on the light screen.

(5) If the upper part of the convex lens is covered with opaque cardboard, the result will be _____.

A. No impact b. Can't image

C. Half image D. A complete image can still be formed, but the brightness becomes darker.

Knowledge point 2. The principle and application of magnifying glass

(1) Principle of magnifying glass: When the object is within 1 times the focal length of the convex lens (i.e. when u

(2) Magnifying glasses with different thicknesses have different magnification factors. The thicker the convex lens, the smaller the focal length and the greater the magnification factor.

(3) When using a magnifying glass, please note: Only when the distance between the object and the magnifying glass is less than 1 times the focal length, can you see the upright magnified virtual image of the object, and within the limit of 1 times the focal length, the farther the object is from the convex lens, the smaller the image will be. The bigger the image.

[Example 3] (2014·Shaoyang) Student A held a magnifying glass with a focal length of 10cm to look at classmate B who was 1.5m away from him. However, student B saw through the magnifying glass a clear, enlarged and upright virtual image of classmate A’s eyes, then The distance between the magnifying glass and classmate A ( )

A. Less than 10cm

B． More than 10cm and less than 20cm

C. Greater than 20cm

D． equal to 10cm

[Exercise 3] One day, Xiao Cong told Xiao Liang that a magnifying glass can not only "enlarge" objects but also "shrink" them! A little surprised, Xiaoliang immediately found a magnifying glass for experiment. When he placed the magnifying glass at a certain position in front of the flower, he saw an upright magnified virtual image of the flower as shown in the picture. Then he followed Xiao Cong's instructions and finally saw the "shrunken" flowers. Regarding Xiaoliang's operation after seeing the "enlarged" flowers and the "shrunk" flowers he saw, which of the following statements is correct ( )

A. Move the magnifying glass closer to the flower, and you will see an upright and reduced virtual image of the flower.

B． Move the magnifying glass closer to the flower, and you will see an inverted and reduced real image of the flower.

C. Move the magnifying glass away from the flower, and you will see an upright, reduced virtual image of the flower.

D． Move the magnifying glass away from the flower, and you will see an inverted and reduced real image of the flower.

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Update Time: 2024-10-15

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