"Lens" Lens and its applications PPT courseware 2

Description

"Lens" Lens and its applications PPT courseware 2

Knowledge point 1 Types of lenses

The lens is a kind of refractor, which is made of glass, quartz and other transparent materials. Its surface is part of the spherical surface. Its optical property is that when light shines on the lens, part of the light is refracted twice by the lens and then changes the optical path to follow the light path. the law of refraction.

Lenses have a certain thickness, and their thickness directly affects their effect on light. In junior high school, we mainly talk about thin lenses. The so-called "thin" means that the thickness of the lens is much smaller than the radius of the sphere.

There are two types of lenses: convex lenses and concave lenses

The straight line on the lens passing through the centers of the two spheres is called the principal optical axis, or the principal axis for short. There is a special point on the main axis of each lens: all light passing through this point has its propagation direction unchanged. This point is called the optical center.

Knowledge point 2 The effect of lens on light

A convex lens has a converging effect on light, which means that after the light passes through the convex lens, the propagation direction of the refracted light is closer to the main optical axis than the propagation direction of the original incident light.

Concave lenses have a divergent effect on light, which means that after light passes through a concave lens, the propagation direction of the refracted light rays deviates further from the main optical axis than the propagation direction of the original incident light rays.

1. The effect of convex lens on light

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

Optical center: center 0 of the lens

Principal optical axis: a straight line passing through the optical center and perpendicular to the lens plane

Focus and focal length of convex lens

A convex lens can make light parallel to the main optical axis converge at a point, which is called the focus (F).

The distance from the focus to the optical center is called the focal length (f). The focal lengths on both sides of the same convex lens are equal.

For a convex lens, the more convex the surface, the shorter the focal length (f), and the stronger the convergence effect.

2. The effect of concave lens on light

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

The focus and focal length of a concave lens

Concave lenses can make light parallel to the main optical axis diverge,

The reverse extension lines of the divergent rays intersect at a point, which is called the focus F (virtual focus).

The distance from the focus to the center of the lens is called the focal length f.

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.

induction:

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". Distinguish whether parallel light rays converge or diverge through a lens.

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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: 2024-06-11

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

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