Assuming that the lens is surrounded by air or vacuum (refractive index 10), the focal length is the distance from the secondary principal point (which in this case is also the secondary nodal point) to the rear focal point of a lens. In this experiment you will determine the focal length of a concave lens in two ways: a) by direct measurement using ray tracing and b) by measuring the radius of curva- ture and using the lensmaker's equation. Thin lens approximation for a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lensfor a converging lens (for example a convex lens), the focal length is positive, and is the distance at which a beam of collimated light will be focused to a single spot. Find an approximate value for the focal length by focusing an image of a distant object onto a sheet of paper the distance from the object to the lens is its focal length approximately measure and record this distance. Aim: to find the focal length of a convex lens by plotting graph between u and v apparatus : an optical bench with three upright (central upright fixed , two outer uprights with lateral movements ), a convex lens with lens holder , two optical needle , (one thin , one thick ) a knitting needle and a half meter scale.
How to determine the radius of curvature of a convex lens ask question up vote 4 down vote favorite determine the focal length of a biconvex lens 1. Determination of the focal length of a convex lens and the focal length of a concave lens by the conjugate foci method: (e) mount the light source s (fig 13-8) near one end of the optical. The focal length of a convex mirror can be determined by introducing a convex lens between the object and the convex mirror an image can be obtained with the help of a convex lens side by side with the object when the convex mirror reflects the rays along the same path, ie, when the rays fall normally on the mirror. By definition, the focal length is the distance between the axis of the lens and the point where the image is formed in a single lens you can measure it easily, go bellow a lamp and measure the distance between the lens and a paper when an image.
The lens converges incoming light rays that are parallel to the optical axis toward a single point on the optical axis called the focal point the distance between the focal point and the center of the lens is called the focal length (f)  of the lens. Aim: to determine the focal length of a convex lens by obtaining an image of a distant object apparatus/material required : a convex lens, convex lens stand, a small screen (hard sheet of white paper/cardboard) fixed. Determination of focal length of convex lens using u-v method the relation between u, v and f for a convex lens is, v-1 + u-1 = f-1 using the proper sign convention, u is negative, u negative, v and f are positive. In the determination of focal length of large focal length lenses, conventionally, a large length of optical bench is needed to accommodate the experimental set-up, and the measurements are associated with bench errors.
Practical-5 focal length of a convex lens by plane mirror method aim: to find the focal length of a convex lens by the plane mirror method apparatus: optical bench, plane mirror, object pin, meter scale and holders. Human eyes were used to determine where the focal point was, and it was hard to determine when the image was perfectly clear on the plastic there was some difficulty lining everything up as well also, there is the possibility that the lens is cut poorly and not quite the focal length specified. A simple experimental procedure is described for the precise measurement of focal lengths of medium-sized convex mirrors this procedure is a modification of the conventional method reported in the literature. The distance from the lens to the focal points is called the focal length for a converging lens, the focal length is always positive, for a diverging lens it is always negative if a lens, diverging or converging, is flipped 180º, the focal points remain in the same place. For the evaluation of the focal length of the convex concave compound lens, f a b d i f for a thin lens or mirror, the magnification of the image may be calculated.
The focal length of the mirror is calculated as , repeat the experiment by moving the convex lens towards the object by 2 cm each time and record the values in a tabular column simulator procedure (as performed through the online labs ). Ttooppss pphhyyssiiccss tops optical bench finding focal length of lenses and mirrorsdoc page 3 1 remove the 75 mm lens and replace it with the 150 mm convex lens. Focal length of a convex lens uv method convex lens or plus lens is a converging lens it may be of biconvex, plano -- convex or concavo- convex (meniscus) the plano-convex lenses are flat on one.
The lamp must be near optical axis of the lens a is distance to lamp, streetlamp, or horizon a' is distance to wall calculate f from a and a' for more info about focal length see focal length on wikipedia. The conventional newton's method can be applied for the measurement of focal lengths of convex lenses the advantages of this method are that it does not require the location of the principal points of the test lens for the measurement of focal length and it can be applied to the thin as well as thick lenses. Converging lenses are convex with a positive focal length and diverging lenses are concave with a negative focal length convex lenses are a series of prisms that get stronger as the outsides of the lens are reached and in this manner, light is refracted to converge on a point called the focus beyond the lens. To determine the focal length of a concave mirror, by obtaining image of a distant object theory a concave mirror, like a plane mirror, obeys the laws of reflection of light.
To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence [delhi 2012] (i) hold the lens between the object and the screen. The focal length of convex lens (f 1) is shown inside the simulator window you can calculate the focal length of the concave lens using the formula f 2 = (f 1 f/(f 1 -f) you can verify your result by clicking on the 'show result' button. The focal length of a convex lens is the distance between the center of the lens and the focal point here, f is the focal point and f is the focal length different lenses converge light at different focal points, and thus, have different focal lengths.