why is focal length taken as positive?
431083
The direction of the incident parallel rays and refracted rays in case of convex lens is the same. So, the distance of the point where the incident rays ,after passing through convex lens ,converge which is called focal length of the lens, is positive. ... This means convex lens does converge parallel incident rays.
683065
The principal focal length of a lens is determined by the index of refraction of the glass, the radii of curvature of the surfaces, and the medium in which the lens resides. It can be calculated from the lens-maker's formula for thin lenses.
2471
Focal Length - The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.
666469
The distance from the lens to that point is the principal focal length f of the lens. For a double concave lens where the rays are diverged, the principal focal length is the distance at which the back-projected rays would come together and it is given a negative sign.
296444
Answer Expert Verified focal length depends upon refractive index of lens with respect to medium. hence, after immersing of lens in water focal length of lens increases.
418828
For focal length, f in lens is always taken as negative for concave and positive for convex. In case of mirror the f is taken as negative if it is in -X side i.e., is in Concave mirror and taken as positive if it is in +X side i.e., is in Convex mirror.
641598
Keeping it simple, focal length has to do with the mm numbers on your lens. Just change the mm numbers on your lens by turning it and you can easily see the differences. Focal distance has to do with focusing on your subject, referring to the distance the subject is from the camera.
117119
The first number indicates the power of the lens required to correct your nearsightedness or farsightedness. If this number is negative, you are nearsighted, or you have difficulty seeing distant objects. A positive number indicates you're farsighted, or you have difficulty seeing close objects.
236586
The focal length of a mirror is given by f2​=v1​−u1​.
286868
The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (e.g., 28 mm, 50 mm, or 100 mm). ... The shorter the focal length (e.g. 18 mm), the wider the angle of view and the greater the area captured.
210844
Focal length, usually represented in millimeters (mm), is the basic description of a photographic lens. ... The longer the focal length, the narrower the angle of view and the higher the magnification. The shorter the focal length, the wider the angle of view and the lower the magnification.
1028362
how does the focal length of a convex lens change if monochromatic red light is used instead of monochromatic blue light? Focal length of the convex lens increases with the increase in wavelength. We know wavelength of red is more than the wavelength of violet.
25423
The magnification of any lens is determined by its focal length. ... A maximum magnification ratio of 1:2 or “0.5x” would mean that the maximum size that an image of the same ½" object could be projected onto the sensor would be ¼", or just half its true size.
370039
A lens with more “bending power” has a shorter focal length, because it alters the path of the light rays more effectively than a weaker lens. ... But for thicker lenses, how thick they are does make a difference, and in general, results in a shorter focal length.
422025
The angle of refraction, and therefore the focal length, will be dependent upon the geometry of the lens surface as well as the material used to construct the lens. Materials with a high index of refraction will have a shorter focal length than those with lower refractive indices.
1176490
The FOCAL LENGTH is effectively the length of the telescope. It is measured as the distance from the main optic to the point where the image is formed. A short focal length will give a wide field of view but the objects in the field of view will appear small.
200072
If the image and object are on the same side of the lens, the image distance is negative and the image is virtual. For converging mirrors, the focal length is positive. ... Note that in certain cases involving more than one lens the object distance can be negative.