"Lens" Common Optical Instruments PPT Courseware 3

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"Lens" Common Optical Instruments PPT Courseware 3

Pre-study tips

1. There are two types of lenses

One type is thick in the middle and thin on the edges, which is called ___________.

One type is thin in the middle and thick at the back, which is called ____________.

2. Convex lenses have a ______ effect on light, and concave lenses have a ______ effect on light.

3. A convex lens has ____ ______ focus points (fill in the blanks), and a concave lens has ___ _____ focus points (fill in the blanks).

Lens classification

1 Convex lens: A lens that is thick in the middle and thin at the edges.

2 Concave lens: A lens that is thin in the middle and thick at the edge.

Research experiment 1:

1. The effect of convex lens on light

Convex lenses converge light, so convex lenses are also called converging lenses.

focus of convex lens

1. The light rays parallel to the main optical axis converge at a point on the main optical axis after passing through the convex lens. This point is called the focus (F) of the convex lens.

2. A convex lens has two real focal points.

2. The effect of concave lens on light

Concave lenses diverge light, so they are also called divergent lenses.

focus of concave lens

The light rays parallel to the main optical axis diverge after passing through the concave lens. The reverse extension line of the divergent rays intersects on the main optical axis. It is not the convergence point of the actual light rays and is called the virtual focus (F).

Research experiment 2:

(1) Explore the light that passes through the optical center of the convex lens and the light that is incident parallel to the main optical axis of the convex lens.

(2) Explore the light that passes through the optical center of the concave lens and the light that is incident parallel to the main optical axis of the concave lens.

Light passing through the optical center of the lens

Conclusion: The direction of light propagation through the optical center does not change.

focal length of convex lens

1. The distance from the focus to the optical center of the convex lens is called the focal length (f).

2. The focal lengths on both sides are equal.

Think about it?

(1) What does the light incident through the focus look like after passing through the convex lens?

(2) What happens to the light incident on the virtual focus on the opposite side of the concave lens after passing through the concave lens?

in conclusion:

(1) The light passing through the focus of the convex lens is refracted and emitted parallel to the main optical axis.

Therefore, parallel light can be obtained by using a convex lens.

(2) The light incident on the virtual focus on the opposite side of the concave lens is refracted and emitted parallel to the main optical axis.

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.

The light incident on the virtual focus on the opposite side of the concave lens is refracted and emitted parallel to the main optical axis.

Exploration Activity: Identify Lens Types

1. Touch (identify according to the structural characteristics of the lens)

2. Illumination (identified based on the effect on parallel light)

3. Look (identify according to the imaging characteristics of the lens)

Ask students to use the lens in your hand to observe the words in the textbook. What changes do you see in the words?

Conclusion: If what you see through a lens is a magnified image, then the lens is a convex lens

If what you see through a lens is a reduced image, then the lens is a concave lens

What did you learn?

1. Classification of lenses:

2. Concept:

1. Main optical axis---the straight line passing through the centers of two spherical surfaces is called the main optical axis of the lens.

2. Optical center (O) --- A special point on the main optical axis through which the propagation direction of light does not change. This point is called the optical center of the lens.

3. Focus (F) ---The light rays parallel to the main optical axis converge at a point on the main optical axis after passing through the convex lens. This point is called the focus.

4. Focal length (f) ---The distance from the focus to the optical center is called the focal length.

3. The effect of lens on light:

1. Convex lenses converge light

2. Concave lenses diffuse light

4. 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 then emitted parallel to the main optical axis. The light incident on the virtual focus on the opposite side of the concave lens is refracted and emitted parallel to the principal optical axis.

Classroom testing

Basic knowledge exercises

Get to know lenses:

(1) A convex lens is a lens with _____ in the middle and _____ at the edges; a concave lens is a lens with _____ in the middle and _____ at the edges.

(2) The lenses of glasses worn by people for myopia are a kind of _____ glasses; the lenses of glasses for farsightedness are a kind of _____ glasses.

(3) Lenses are divided into two categories: _____ lenses and _____ lenses.

(4) Several concepts of lenses:

Main optical axis: The straight line passing through the centers of the two spheres is the main optical axis. As shown in the figure, __________ is the main optical axis.

Optical center: refers to the point where light passing through this point remains unchanged. As shown in the figure, the _____ point is the optical center.

Focus: ＿＿＿＿＿＿＿＿＿＿, focus can be divided into real focus and virtual focus;

A convex lens has a __focus, and a concave lens has a __focus (but it actually cannot converge light).

Focal length: refers to _______________

Object distance: refers to _______________

Image distance: refers to _______________

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Update Time: 2024-11-21

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