Uses of Concave and Convex
The Convex mirrors spread parallel rays of light further apart as shown here. The reflected rays seem to come from behind the mirror, so the image is virtual, as in a flat mirror. Such mirrors have a wide field of view. This is why they are used as rear-vision mirrors. They are also used for surveillance in shops and to help motorists see around blind corners. The Concave mirrors reflect parallel rays of light closer together to form a real image at the focus. In a reflecting telescope a concave mirror and a flat mirror together form a tiny image of a distant star. This image is then magnified by the eyepiece lens. The larger the mirror the more light it collects from the star.
Reflection affects Concave and Convex
A mirror that curves outwards like the outside of a spoon is called a convex mirror. A beam of light shone onto a convex mirror diverges (spreads out). The point where the beam appears to come from is called the focus. A convex mirror can only form virtual images. If a mirror curves inwards like a cave it is called a concave mirror. If a parallel beam of light is shone onto a concave mirror, the light is made to converge (come together) to a point called the focus. The focal length of the mirror is the distance of the focus from the mirror’s reflecting surface. Concave mirrors can form either real or virtual images, depending on where the object is compared to the focal point.
Upside Down
The rays from any object at finite distance are divergent when they arrive and the convex mirror makes them more divergent. When a given ray reaches your eye it's in the same part of the image as when it arrived, so the image is upright.
The concave mirror brings these rays to a virtual focus behind the mirror if the object is nearer the mirror than the focal point. This image is upright. If the object is beyond the focal point the image is real and inverted.
The Convex mirrors spread parallel rays of light further apart as shown here. The reflected rays seem to come from behind the mirror, so the image is virtual, as in a flat mirror. Such mirrors have a wide field of view. This is why they are used as rear-vision mirrors. They are also used for surveillance in shops and to help motorists see around blind corners. The Concave mirrors reflect parallel rays of light closer together to form a real image at the focus. In a reflecting telescope a concave mirror and a flat mirror together form a tiny image of a distant star. This image is then magnified by the eyepiece lens. The larger the mirror the more light it collects from the star.
Reflection affects Concave and Convex
A mirror that curves outwards like the outside of a spoon is called a convex mirror. A beam of light shone onto a convex mirror diverges (spreads out). The point where the beam appears to come from is called the focus. A convex mirror can only form virtual images. If a mirror curves inwards like a cave it is called a concave mirror. If a parallel beam of light is shone onto a concave mirror, the light is made to converge (come together) to a point called the focus. The focal length of the mirror is the distance of the focus from the mirror’s reflecting surface. Concave mirrors can form either real or virtual images, depending on where the object is compared to the focal point.
Upside Down
The rays from any object at finite distance are divergent when they arrive and the convex mirror makes them more divergent. When a given ray reaches your eye it's in the same part of the image as when it arrived, so the image is upright.
The concave mirror brings these rays to a virtual focus behind the mirror if the object is nearer the mirror than the focal point. This image is upright. If the object is beyond the focal point the image is real and inverted.
Focal Length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more strongly, bringing them to a focus in a shorter distance.
Convex Lens
The methods already described for finding the focal lengths of lenses involve the measurement of distances from the lens surface, and consequently a certain amount of error is caused by neglecting the thickness of the glass of which the lens is composed. This becomes very important, in the case of short-focus lenses and of lens combinations. The following method avoids the difficulty by rendering the measurement from the lens surfaces unnecessary.
Lens
Another characteristic of the images of objects formed by diverging lenses pertains to how a variation in object distance affects the image distance and size. The diagram below shows five different object locations (drawn and labeled in red) and their corresponding image locations