"Laws of Imaging by Convex Lenses" Lenses and Their Applications PPT Courseware 7

Description

"Laws of Imaging by Convex Lenses" Lenses and Their Applications PPT Courseware 7

1. Knowledge objectives of this section

1. Ability to measure the focal length of convex lenses

2. What are the rules of imaging through convex lenses?

Ask a question:

Teacher guides questions:

Cameras, projectors, and magnifying glasses all use convex lenses to create images. Do they all produce the same image?

The same image is formed by a convex lens, but the size, upright and inverted images are so different. What does this have to do with it?

Conjectures and assumptions:

Students come up with conjectures and hypotheses:

(1) Whether the image formed by a convex lens is enlarged or reduced may be related to the distance from the object to the convex lens.

(2) The inversion of the image formed by a convex lens may be related to whether the image and the object are on the same side of the convex lens.

conduct experiment:

Students do the following:

1 Use your own method to obtain the focal length of a convex lens.

2 Understand the light bench, and place the experimental equipment on the light bench in the order of candles, convex lenses, and light screens.

3. The candle flame passes through a convex lens to form a real image of equal size, and the object distance and image distance are recorded.

4. The candle flame passes through the convex lens to form a magnified real image, and the object distance and image distance are recorded.

5 The candle flame is transformed into a reduced real image through a convex lens, and the object distance and image distance are recorded.

6 The candle flame passes through the convex lens to form a magnified virtual image, and the object distance is recorded.

7 Do the above imaging process again.

Assessment and communication:

In convex lens imaging, when the object moves, where is the turning point between the real image and the virtual image? Where is the transition point between enlarging and reducing the real image? (Ask students to answer)

Memory tips:

(One focal length is divided into reality and reality; twice the focal length is divided into large and small.)

Rule one:

Characteristics of the image: inverted, reduced, real image

Characteristics of the image: inverted, magnified, real image

Characteristics of the image: upright, magnified, virtual image

Rule 2:

When the object distance is greater than the focal length

When the object distance increases, the image distance decreases, and the image also decreases.

When the object distance decreases, the image distance increases and the image also increases

When the object distance is smaller than the focal length

When the object distance decreases, the image distance decreases

Rule three:

When the image formed is a real image, the object and image are on different sides

When the image formed is a virtual image, the object and image are on the same side

Rule 4:

1. The focus is the dividing point between real and virtual images. Objects outside the focus become a real image, and objects within the focus become a virtual image. One focal length separates virtual reality from reality.

2. The double focal length is the dividing point between enlarged and reduced images. Objects become a reduced image beyond twice the focal length, and an enlarged image within twice the focal length. The focal length is divided into two sizes.

Class exercises

1. Place the object 16 cm in front of the convex lens and obtain an inverted and reduced image on the light screen. Then the focal length of the convex lens may be ( )

A. 10cm B. 7cm

C, 8cm D, 16cm

2. When the candle is 36 cm away from the convex lens, its image is clearly reflected on the light screen on the other side 20 cm away from the lens. What is obtained on the light screen is a _______, _______ image of _______.

3. Take a picture of a classmate with a camera with a constant focal length, and a clear full-length image will appear on the film. If you want to change the picture to a bust, the camera should ( ) (fill in closer or farther away from) the classmate, and the lens should be ( ) farther away from the film.

4. A slide was shown for students in a certain school to carry out legal education on "cherishing life and staying away from drugs". It was found that the image on the screen was a little smaller, the projector was farther away from the screen ( ), and the film was farther away from the lens ( ).

Classwork:

1. In the observation experiment of convex lens imaging, it is known that the focal length of the convex lens is 10cm. If a lit candle is placed 25cm in front of the convex lens, a clear image will be formed on the light screen: ( )

A. Inverted and reduced real image B. Upright and reduced real image

C. Inverted magnified real image D. Upright magnified virtual image

2. When doing the experiment of observing "convex lens imaging", the object is placed 60cm away from the convex lens, and an inverted and reduced real image is obtained on the light screen, then the focal length of the convex lens may be ( )

A, 20cm B, 30cm C, 60cm D, 80cm

3. A student used a magnifying glass with a focal length of 10cm to observe the text on the book. When he saw the upright magnified text, the distance from the text to the convex lens is ( )

A. 25cm B. 15mm C. 6cm D. 12cm

4. When the object moves from 8f to 2f, the image is always _____, but the image gradually becomes _____.

Class summary

1. Through the exploration in this lesson, do you know what the rules of imaging by convex lenses are?

2. Please tell the students what new gains they have gained from today’s class?

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