In this experiment, we will be dealing only with thin lenses. You will do this by constructing a graph of 1 q vs 1 p and using eq. Objective to measure the focal length of convex positive or convergent lenses and concave negative or divergent lenses. Experiment aim to find the focal length of a convex lens by plotting graphs between u and v or between 1 u and 1 v. An advantage of this method is that it gives accurate results because the distance, a, is independent of the thickness of the lens and the position of the lens in the lens holder.
The focal length of the concave lens l 2 can be calculated from the r elation. Finding the focal length of a convex lens by plotting. Is that image the focal point or is it just the distance of the image. I am trying to find the focal length of a convex lens, so i let the sun shine through my window to create an image on my wall.
Converging lenses are convex lenses that converge to the central axis. Lab preparation the picture on the screen in a movie theater is called a real image. Determination of focal length of concave mirror and convex lens. In addition, for spherical mirrors the focal length is half the radius of curvature of the reflecting surface. However, light cannot be focused through a diverging lens to form a real image unless that light was already converging. To find the focal length of a convex mirror using a convex lens. For this purpose, indirect method is used, as described below. Thin lenses, converging lens, diverging lens, lens equation, object distance, image distance, refraction, focal length, magnification, index of refraction, real. Measuring the focal length of a converging lens in this experiment, you will measure a series of object distances and corresponding image distances for a converging lens and calculate its focal length. Two convex lenses of different focal length and an optical bench with four uprights. Physics 2 lab report 7 focal length of lenses focal. Practical5 focal length of a convex lens by plane mirror method.
Arrange the plane mirror, convex lens and object pin with help of holder. Experiments to measure the focal length of a converging lens the position of the lens holder is adjusted until a sharp image of the object is formed on the screen alongside the object itself. For a curved mirror, the radius of curvature, r can be defined as the radius. Equation 4 can be rewritten simply in terms of power as. Practical5 focal length of a convex lens by plane mirror. To determine the focal length of a spherical convex lens by lens formula method by lens replacement method. Clamp the holder with lens in a fixed upright and keep the upright at 50 cm mark. Convex lens converges all the rays and the distance between lens and focus is 40 cm.
The focal length for convex lenses never changes with it being on the power of the lens. The purpose of this experiment is to determine the focal length of a thin converging lens. For a converging lens, the focal length is always positive, for a diverging lens it is always negative. Procedure to determine rough focal length of convex lens. Dec 01, 2016 as a concave lens always forms a virtual image, its focal length can not be found directly as for a convex lens. An object outside the lens focal point forms a real and inverted image on the side of the lens opposite the object. Difference between convex and concave lens with figure. We also touch upon the applications of lenses in daytoday life.
As a concave lens always forms a virtual image, its focal length can not be found directly as for a convex lens. Keep the distance between the plane mirror and convex lens as 30cm, 40cm for other set of the readings 4. Optical bench, plane mirror, object pin, meter scale and holders procedure. When the object is outside the converging lens focal point, f, the resulting image is real, inverted and on the side of the lens opposite the object. In this experiment, we have chosen two methods to find out the focal length of a spherical lens. Overview of various methods for measuring a lens focal length. In addition, for spherical mirrors the focal length is. Focal length of a converging lens distance learning lab. The purpose of this experiment is to determine the focal length of a thin lens and to measure the magnification for a certain combination of object and image distances. To accomplish this, a real image from a converging lens will. To verify the expression for the focal length of a combination of two lenses. Fizeau interferometry the length focal length is calculated using the following formula.
Generally, a convex lens forms a real image, but it can also create a virtual image when the object is in the middle of the focus and optical centre. Focal length of lenses march 24, 2009 when an object is placed at a distance p from a convex lens with focal length f, then if p f, a real image is formed at some distance i away from the lens see the figure below. Finding the focal length of a convex lens by plotting graph. Determination of focal length of concave lens using convex. Cbse class 10 science lab manual focal length of concave. The focal length of a convex lens experiments to measure the focal length of a converging lens method 1. For a thin double convex lens,refractionacts to focus all parallel rays to a point referred to as the principal focal point. Dec 08, 2018 the focal length of a convex lens is positive, while that of a concave lens is negative. The red lines are a representative sample of light rays emanating from. To find the focal length of a convex lens by plotting. The lens used above is convex and the focal length is positive. Jun 08, 2016 focal length of a convex lens practical experiment c. In this section of the experiment, we will use two lenses to form a real image of the virtual image from a concave negative focal length lens. Diverging lenses are concave lenses where the rays diverge.
Determination of focal length of a converging lens and mirror. And if it is the distance of the image, how do i put it into the thin lens equation, since the. Measure the focal length from the center of the convex lens to the focal point. Repeat the experiment for a variety of object distances, ensuring it is always greater than the approximate focal length. An object needle o is placed on one side of a convex lens l 1 and its real inverted image i is located by image needle on the other side as shown in ray diagram. The distance between the convex lens and object pin is the focal length of the convex lens. Jan 17, 2020 a the device x is a convex lens of focal length 20 cm. This is shown with the geometrical ray diagram of figure 4. Physics 215 experiment 14 thin lenses 79 advance reading urone, chapter 24, section 246 objective. Before getting started with the experiment, it is important to understand a few terms that are used in a concave mirror and convex lens centre of curvature. For a thin lens in air, the distance from the lens to the spot is the focal length of the lens, which is commonly represented by f in diagrams and equations. Measure the distance between the screen and mirror image distance. Measure the approximate focal length of the lens by focusing a distant object onto a screen and measuring the distance from the lens to the screen using the metre stick.
A thin convex lens can be characterized by its focal length f, the. According to the author, this method gives the focal length value with less than 1% accuracy. Visualizing a virtual image is possible but dicult. On the contrary, the image formed by the concave lens is erect, virtual and smaller, than the object. Determination of the focal length and the power of a diverging concave lens 5. Note that in step 2, the rays leaving the lens are diverging and they will not cross. We use the lens formula in this experiment to calculate the focal length of the concave lens. The second image a b is formed only when the distance between lens l 2 and first image a. As a preliminary step to determine approximate focal length of the converging lens, form image of a distant object on a white paper. Lenses produce different types of images, depending on the position of the object relative to the lens and its focal point. Light refracts when passing through media with different indices of. For a normal eye, when the eye muscles are relaxed, the focal length f of the lens l is slightly less. The objective of this experiment is to measure the focal length of a converging lens and a diverging lens.
The lens is set up in a suitable holder with a plane mirror behind it so that light passing through the lens is reflected back again fig. This experiment deals with 4 different ways of measuring the focal length of a double convex lens. Determination of focal length of concave mirror and convex. To determine the focal length of a lens using the ray box. Repeat the above procedure with the other lens and determine the focal length f2. An extended hemispherical lens is a special type of plano convex lens, in which the lens s curved surface is a full hemisphere and the lens is much thicker than the radius of curvature. It is made by light from an object passing through a converging lens as shown in figure 1.
The relation between u, v and for a convex lens is. 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 lens. To find the focal length of a convex lens by plotting graphs between u and v and between 1u amd 1v. Move the screen back and forth until the image of the crossthreads is in sharp focus.
Jun 26, 2016 experiments to measure the focal length of a converging lens method 1. For 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. Focal length is the distance between optical centre of lens. Measure the approximate focal length of the lens by focusing a distant object onto a screen and measuring the distance. Theory a lens is a transparent object with two refracting surfaces whose central axes coincide. The mean of focal length of both the faces is the focal length f1 of one lens.
The student should study a relative chapter of college physics textbook before performing this experiment. To find the focal length of a concave lens using a convex. Objects appear different when viewed through convex lenses depending on how you hold them. Apparatus and material required an optical bench, two sharpedged needle pins, convex lens of less than 20 cm focal length, three uprights with clamps. These two variables are related to the focal length, f, by the lens equation. Cbse class 10 science lab manual focal length of concave mirror and convex lens experiment 4a aim to determine the focal length of concave mirror by obtaining the image of a distant object. Experiment 4finding the position of a virtual image. Your lab report for this experiment should contain the following sections. Determine the focal length of a converging lens using the provided measurements of object and real image distances. A thin convex lens can be characterized by its focal length f, the object distance, d o and the image distance, d i. Nov 30, 2016 procedure to determine rough focal length of convex lens. To find the focal length of a convex lens by plotting graphs between u and v or. Experiment 1 measuring the focal length of a convex lens parallax method experiment 2 investigating the relationship between the image and object distance for a convex lens. Focal length of convex lensb11 lab report objectives of the experiment.
Practical5 focal length of a convex lens by plane mirror method aim. Record the position of the plane mirror, convex lens and the object pin. Convex lenses of at least two different focal lengths, metric measuring tape. Focal length of a convex lens practical experiment youtube. Look at the image of a distant object it could an object outside the window and measure the distance between the image and the lens. In this experiment, we have chosen two methods to find out the focal length of a. A convex is lens is thicker the further to the centre of the lens. To find the focal length of a convex mirror, using a convex lens. Finding the focal length of a lens using the ray box. We will also find out how to work out the u object distance, v image. Because of its ability to focus light a converging lens can produce an image of an object, as represented in fig. Diverging lens to determine the focal length of a diverging lens, the lens must create a measurable, real image as in part 1. Focal length of a convex lens practical experiment c.
For a curved mirror, the centre of curvature, c can be defined as the centre of a hollow glass sphere of which a curved mirror is a part. To determine the focal length of a thin lens and to explore the difference between convex and concave lenses and to determine their focal lengths. If a lens, diverging or converging, is flipped 180. Convex lens, optical bench, light source, target image slide, lens mounts.
To measure the focal length of a converging lens using various methods and to study how a converging lens forms a real image. Equipment materials ray box with illuminated object, white screen, lens holder, metre rule and lens background the purpose of the experiment is to study image formation by a thin lens. To find the focal length of a convex mirror, using a. The purpose of this experiment is to verify the thin lens equation and to construct simple optical systems using various combinations of lenses.
Ncert class 10 science focal length of concave mirror and. Mar 17, 2020 determine the focal length of a converging lens using the provided measurements of object and real image distances. The object and image are denoted by the line segments aband a0b0. Materials required a concave mirror, a mirror holder, a small screen fixed on a stand, a measuring scale and a distant. Experiments to measure the focal length of a converging lens. A careful examination of this equation will show that this method cannot be used unless b 4f. Materials required a concave mirror, a mirror holder, a small screen fixed on a. The distance from the lens to that point is the principal focal length f of the lens. Apparatus and material required an optical bench, two sharpedged needle pins, convex lens of less than 20 cm focal length, three uprights with clamps, index needle may be a knitting needle, metre scale and spirit level. Teacher packs in experimental science phy pack 5 finding the.
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