Concave mirror and convex mirror belong to the category of reflecting mirror. Concave mirror has the function of concentrating light, and convex mirror has the function of diverging light, thus expanding the field of vision. The convex mirror widely used in life is the mirror beside the car; Solar cooker is the most widely used convex mirror.
Imaging law of convex lens
When an object is out of focus, it becomes an inverted real image on the other side of the convex lens. There are three kinds of real images: reduction, equal division and enlargement. The smaller the object distance, the larger the image distance and the larger the real image. The object is placed in focus and becomes an upright magnified virtual image on the same side of the convex lens. The smaller the object distance, the smaller the image distance and the smaller the virtual image.
In optics, the image formed by the convergence of actual light rays is called real image; On the contrary, it is called a virtual image. Experienced physics teachers, when talking about the difference between real images and virtual images, often mention such a distinction method: "Real images are upside down, and virtual images are upright." The so-called "positive" and "negative" are of course relative to the original image.
The three virtual images formed by plane mirror, convex mirror and concave lens are all positive; The real image formed by concave mirror and convex lens, and the real image formed by pinhole imaging are all inverted without exception. Of course, concave mirror and convex lens can also become virtual images, and the two virtual images they form are also upright.
So is the image of the human eye a real image or a virtual image? We know that the structure of the human eye is equivalent to a concave lens, so the image formed by external objects on the retina must be a real image. According to the above rule of thumb, it seems that the object image on the retina should be inverted. But anything we usually see is obviously upright. This problem, which conflicts with the rule of experience, actually involves the regulation of cerebral cortex and the influence of life experience.
When the distance between the object and the convex lens is greater than the focal length of the lens, the object becomes an inverted image. When an object approaches the lens from a distance, the image becomes larger and the distance from the image to the lens becomes larger. When the distance between the object and the lens is less than the focal length, the object becomes an enlarged image. This image is not the convergence point of the actual refracted light, but the intersection point of their opposite extension lines, which can not be received by the light screen and is a virtual image. It can be compared to a virtual image formed by a flat mirror (the light curtain can't receive it and can only see it with the eyes).
When the distance between the object and the lens is greater than the focal length, the object becomes an inverted image. This image is formed by the light from the candle converging on the convex lens, which is the convergence point of the actual light and can be accepted by the light curtain. This is a real image. When the distance between the object and the lens is less than the focal length, the object becomes an upright virtual image.
Difference from convex lens
I. Different structures
A convex lens is composed of a transparent mirror, and both sides of the mirror are ground into spheres.
Concave mirror consists of a concave surface and an opaque mirror on the other side.
2. Different effects on light
A convex lens mainly refracts light.
Concave mirror mainly reflects light.
3. Different imaging characteristics
A convex lens is refractive.
Concave mirror is a convex lens for reflection imaging, and the image formed by refraction imaging can be positive or negative; Virtual and real; Expansion and contraction. Play the role of spotlight
Concave mirror is a reflection image that can only be restored to an upright image. A lens (including a convex lens) that plays the role of astigmatism is an instrument that transmits light and forms an image by folding it. Light respects the law of refraction. Mirrors (including convex mirrors) are not instruments that let light pass through, but reflect back images, and light respects the law of reflection.
The convex lens can be an inverted enlarged, equal-sized and reduced real image, or an upright enlarged virtual image. Parallel light can also converge, and the light emitted from the focus can be refracted into parallel light. The convex mirror can only form a vertical and reduced virtual image, which is mainly used to expand the field of vision.