Lens: An optical element made of transparent material (usually glass), at least one surface of which is a part of a spherical surface and can refract light.

Classification: 1, convex lens: thin edge and thick center.

2. Concave lens: thick edge and thin center.

Principal optical axis: a straight line passing through two spherical centers.

Optical center: there is a special point on the main optical axis, through which the propagation direction of light remains unchanged. (The center of the lens can be considered as the optical center.)

Focus: The point at which the convex lens can converge the light parallel to the main axis on the main optical axis, which is called the focus of the lens, and is denoted by F..

Virtual focus: the light parallel to the main optical axis becomes divergent after passing through the concave lens, and the backward extension line of the divergent light intersects with a point on the main optical axis, which is not the convergence point of the actual light, so it is called virtual focus.

Focal length: the distance from the focal point to the optical center is called focal length, which is expressed by F.

Each lens has two focal points, a focal length and an optical center.

The influence of lens on light;

Convex lens: convex light.

Concave lens: It diverges light.

Second, the lens in life

Camera: the lens is equivalent to a convex lens, and the light emitted by the object converges on the film through the camera lens to form an inverted and reduced real image.

Projector: The lens is equivalent to a convex lens. The light from the slide is imaged by a convex lens, and then the propagation direction of the light is changed by a plane mirror, so that the screen becomes an inverted enlarged real image.

Magnifier: a virtual image magnified vertically.

Thirdly, explore the law of convex lens imaging.

Experiment: Put candles, convex lenses and light screens from left to right.

1, adjust their positions so that they are on the same straight line (without using the optical bench); 2. Adjust them so that the center of the candle flame, the center of the convex lens and the center of the light screen are at the same height.

Imaging law of convex lens;

Attribute Application of Object Distance (U) Image Distance (U) Image

U 2f inverted miniature real-image camera

U = 2f= 2f Reverses the equal real image (real image size transition)

F2f 2f inverted magnifying real image slide projector

U = f no imaging (turning point of image)

U f vertical magnifying virtual image magnifying glass

Oral memory method of convex lens imaging law

Oral decision 1: one focus (point) is divided into virtual reality, and the other focus (distance) is divided into size; The same side of the virtual image is positive; The real image is on the opposite side, far smaller.

Oral decision 2:

The reality of distant things is small and close, and the reality of near things is big and far.

If the object is focused, the virtual image is immediately enlarged;

The slide is so big that things are between one focus and two.

If the camera shrinks you a little, the focal length of the object will be twice as far.

Oral decision 3:

Convex lens, high power, photography, slide show, magnification;

Double Jiao Wai is actually very small, and double coke is actually very big;

If the object is in focus, the virtual image on the same side of the object is large;

Remember a rule, birds of a feather flock together.

Note 1: In order to make the image on the screen stand upright (upward), the slide should be inserted backward.

Note 2: The lens of a camera is equivalent to a convex lens, and the film in the camera box is equivalent to a light screen. We adjust the focus ring, not the focal length, but the distance from the lens to the film. The farther the object is from the lens, the closer the film is to the lens.

Four, eyes and glasses

Eye: The lens in the eye works together with the cornea as a convex lens, which focuses the light from the object on the retina to form an image of the object. Optic nerve cells in the retina are stimulated by light and transmit signals to the brain. When looking at distant objects, the ciliary muscle relaxes and the lens becomes thinner (long focal length and weak deflection). When looking at nearby objects, the ciliary muscle contracts and the lens thickens (short focal length and strong deflection).

The performance of myopia: you can see the near objects clearly, but you can't see the distant objects clearly.

Causes of myopia: the lens is too thick, the refractive power is too strong, or the front and back direction of the eyeball is too long, resulting in the image of distant objects in front of the retina.

Myopia correction: wear concave lenses.

The performance of farsightedness: you can see distant objects clearly, but you can't see nearby objects clearly.

Causes of hyperopia: the lens is too thin, the refractive power is too weak, or the anterior-posterior direction of the eyeball is too short, resulting in images of distant objects behind the retina.

Correction of hyperopia: wearing a convex lens.

Glasses degree:/kloc-the reciprocal of 0/00 focal length ().

Verb (abbreviation for verb) microscope and telescope

Microscope: the objective lens has a short focal length, through which the object becomes an inverted magnified real image (like the lens of a projector); The eyepiece has a long focal length, and the image formed by the objective lens forms an enlarged virtual image (like a magnifying glass) through it.

Telescope: (Kepler telescope) The objective lens is used to make distant objects become real images near the focus, and the eyepiece is used as a magnifying glass to enlarge the images.

Note: galileo telescope eyepiece is concave lens, and concave mirror crop mirror is commonly used in astronomical telescope.

Angle of view: the angle between the edge of an object and the eye. The larger the viewing angle, the larger the image.