Hence, calculate the value of focal length for different distances using above formula. Measure the focal length from the center of the convex lens to the focal point. 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. Convex lens, optical bench, light source, target image slide, lens mounts, and screen. Nov 30, 2016 to find the focal length of a convex mirror, using a convex lens. Converging lens rules for ray tracing with converging lens. Ncert class 10 science lab manual image formation by a convex. Equipment 1 optical bench, several convex and concave lenses, 1 light. Experimental setup for determining the focal length of a lens. Read the following passage and answer the questions that follow. Focal length of a converging lens distance learning lab.
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. The relation between u, v and for a convex lens is. Finding the focal length of a convex lens by plotting. The focal length of a bi convex thin lens is 10 cm. Convex lens, optical bench, objects and image pins, meter rule. A convex lens, stand, wire gauze object, screen and measuring scale. Incident rays parallel to the optical axis refract through the far focal point. For lenses used in the lab f lens by using a plumb line and half meter scale. To find the focal length of a convex lens by plotting graphs between. Focal length of convex lens experiment pdf squarespace. Concave lens the method of determining the focal length of a concave negative, diverging lens will involve using it in conjunction with an auxiliary convex positive, converging lens. Find the focal length of the converging convex lens by any. 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.
Apparatus an optical bench with four uprights two fixed uprights in middle, two outer uprights with lateral movement, convex lens 20 cm focal length, convex mirror, a lens holder, a mirror holder, two optical needles, one thin, one thick a knitting needle, and a half metre. The relationship between the focal length f of a lens, the object distance u and the image distance v is. In this case, place the convex lens at about 15 cm from the light source, which is about halfway between the focal length f 10. The relationship between u and v and the focal length f for a convex lens is given by. 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. Recall from a previous lab that the main property of a lens is its focal length, which results from the shape of the lens. Cbse physics lab manual for class 10 pdf download 4. The distance between the convex lens and the image. Also measure the distance between tip of needle and upper surface of the mirror. Experiment 1 experiment 1 determination of the focal length.
Result the focal length of the given lens is 10 cm. 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. A parallel light beam is produced with the lamp and the double condenser. If y o is the height of the object and y i the height of the image, then the magnification m of the lens is.
Determination of the focal length of a convex lens and the focal length of a concave lens by the rte foci method. Mount the convex lens lt such that the object distance sl1. Focal length f f is positive for converging and negative for diverging lenses. Your lab report for this experiment should contain the following sections.
Put the object screen with arrow slit directly behind the condenser, and a clear image. Cbse class 10 science lab manual focal length of concave. To find the focal length of a convex mirror using a convex. Conduct this experiment for the two possible orientations of the plano convex lens. Cbse physics lab manual class 10 chapters wise download here in pdf format. The power p of a lens is one over the focal length, 1 f, and is given in diopters.
Below is the derivation of the lens formula following graphic illustrates a simple lens model. For fullframe 35 mmformat cameras, the diagonal is 43 mm and a typical normal lens has a 50 mm focal length. Focal length f is positive for converging and negative for diverging lenses. For a diverging lens for example a concave lens, the focal. Measuring the distance between the lens optical centre and the point of focus gives the focal length of the lens. To determine the focal length and hence the power of a convex lens by displacement method with the help of an optical bench. The lens used above is convex and the focal length is positive. To determine the focal length of a spherical convex lens by lens formula method by lens replacement method. Practical5 focal length of a convex lens by plane mirror. Record the position of the plane mirror, convex lens and the object pin. In this video we will perform an experiment to determine focal length of convex lens by plotting a graph between u and v. Slide the screen along the track on the far side of the lens until the sharpest possible image is projected onto the screen. Perform this experiment in calm air to avoid the flickering of the candle flame.
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. Objective to measure the focal length of convex positive or convergent lenses and concave negative or divergent lenses. The most important property of a lens is its focal length, or the distance from the lens at which it forms an image from an object infinitely far away. Determination of the focal length of an unknown convex lens by using thin lens equation method 1. If the object is placed very far away from the lens d o. For lenses used in the lab f focal length of lenses and mirrors. Focal length of convex lensb11 lab report objectives of the experiment.
Here, u is the distance between the object light source and the convex lens. Determination of focal length of a convex lens physics laboratory. The distance between the convex lens and the image, measured roughly with a meter rule would give the approximate focal length of the lens. Determination of focal length of concave mirror and convex. This mean distance will be equal to the focal length of the convex lens f1. The focal lengths of a biconvex lens and a concave mirror are shown in figures 1 and 2, respectively. Measurement of the focal length of a converging lens. Of course an image will not be able to focus on your screen as the image formed is virtual. For a red light beam, the refractive index of a thin lens is 1. For a converged lens the focal length is always positive, for the diverging lens it is always negative. An important property of a lens is its focal length, f. It is made by light from an object passing through a converging lens as shown in figure 1. To determine the focal length of a convex lens is a very interesting exercise. To accomplish this, a real image from a converging lens will.
Determine the focal length of a converging lens using the provided measurements of object and real image distances. Determination of focal length of a convex lens physics. 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. Calculate the focal length of the convex lens by using the formula given. Assume that the refractive index of the lens material n.
You can experiment with the principle of this activity, without using tubes. If f is the focal length of equi convex lens, then what will be focal length of the plano convex lens. Focal length of convex lens by plotting a graph between u and. An important property of a lens is its focal length.
To determine the focal length of a convex lens by using. R 11 and r 2 2 are positive for convex outward surface and negative for concave surface. If the object and the image screen be so placed on an optical bench that the distance d between them is greater than four times the focal length f of a given convex lens, then there will be two different positions of the lens for which. The distance from the lens to that point is the principal focal length f of the lens.
Determine the focal length approximately by generating the image of a distant object on a screen. A thin convex lens can be characterized by its focal length f, the object distance, do and the. Theory a lens is a transparent object with two refracting surfaces whose central axes coincide. Teacher packs in experimental science phy pack 5 finding the. Note that in step 2, the rays leaving the lens are diverging and they will not cross. In this case, place the convex lens at about 15 cm from the light source, which is about halfway between the focal length f. The above steps is repeated using lens made from gel wax with 1. Before getting started with the experiment, it is important to understand a few terms that are used in a concave mirror and convex lens. For p experiment, we were able to achieve the objectives of the experiment. Focal length of convex lens experiment pdf converter wkuc. Where f is the focal length, u is the distance between the object and the lens v is the distance between the image and the lens. The focal length of a convex concave thin lens is 20 cm. Focal length of a converging lens advanced physics 2 lab.
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. The focal length of the concave lens l 2 can be calculated from the r elation. Measure distance between tip and upper surface of the lens by using a plumb line and half meter scale. A lens holder, a converging convex lens, an optical bench, a lightbulb socket, a lowwatt light bulb, a rectangular target, a target holder, and a tape measure.
Focal length of convex lens experiment report squarespace. Measurement of focal length of the given lens hbcsetifr. For a thin double convex lens,refractionacts to focus all parallel rays to a point referred to as the principal focal point. To obtain the position of image for a given object distance and focal length of a lens, the following lens formula can be used. If the object is sufficiently far away so that sf, the incoming rays will be almost parallel, and the object will be focused at approximately the focal point of the lens. The second image a b is formed only when the distance between lens l 2 and first image a. Practical5 focal length of a convex lens by plane mirror method. Length of the index needle as measured by the metre scale, l 0.
Read the following passage and answer the questions that. For an object that is infinitely far away, the image distance and the focal length are the same. Measure the image distance and compare it to your prediction. To find the focal length of a convex mirror, using a convex lens. Also, on windows computers, swf files can be played online wit. Experiment 1 experiment 1 determination of the focal. Tops optical bench finding focal length of lenses and mirrors. In this experiment, we have chosen two methods to find out the focal length of a spherical lens. Using these methods, i determined the focal length of two convex lenses to within various degrees of the rated value of the lens.
Repeat the measurement by adjusting the distance between lamphousing and the screen s to roughly about 5. To measure the focal length of a converging lens using various methods and to study how a converging lens forms a real image. Materials required a concave mirror, a mirror holder, a small screen fixed on a. Convex lens three methods will be used to measure the focal length of a convex lens. The focal length of the convex lens must be between 15 to 20 cm. Determination of focal length of concave mirror and convex lens. Students use an optics light source, optics track, and viewing screen to measure the image and object distances associated with the real image formed by a. Determination of focal length of concave lens using convex. For a curved mirror, the radius of curvature, r can be defined as the radius of. These two variables are related to the focal length, f, by the lens equation. Ray diagram for an object infinitely far away from the lens.
To determine the focal length of converging lens and its radius of curvature. One characteristic feature of all thin lenses and concave mirrors is the focal length, f, and is defined as the image distance of an object that is positioned infinitely far way. Ataree3 1 hbcsetifr, mumbai 2 retired teacher siddharth college, mumbai 3 nes school, mumbai abstract. Finding the focal length of a lens using the ray box. Finding the focal length of a convex lens by plotting graph. Determination of focal length of a converging lens and mirror.
The experiment is to enable students to physically observe the image produced by the lens. Lens are used to manipulate light in many instruments. Move the 75mm lens and its component holder back and forth on the bench until the image of the arrow is focused on the screen. Determination of focal length of a convex lens physics laboratory practical experiment study material, lecturing notes, assignment. If placing them in parallel and in close contact, what is the compound focal length. We use the lens formula in this experiment to calculate the focal length of the concave lens. Visualizing a virtual image is possible but dicult. To nd the di erence in the focal length obtained for the two lens orientations, determine the location and separation of the principal planes of your lens. 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. Place the object inside the focal length of your convex lens.
Focal length is the distance between optical centre of lens. The distance between the point where light ray converge after passing through the lens and the centre of lens is recorded, the distance obtained is the focal length, f of the lens as shown in figure 6. To find the focal length of a convex mirror using a convex lens. We can conclude the focal length of the convex lens which are 9. Keep the distance between the plane mirror and convex lens as 30cm, 40cm for other set of the readings 4. This distance equals the focal length of the group of lenses f g. Place a second convex lens to the right of the first. Determination of the focal length of a concave lens using a convex lens 9.
As a preliminary step to determine approximate focal length of the converging lens, form image of a distant object on a white paper. Measure the approximate focal length of the lens by focusing a distant object onto a screen and measuring the distance from the lens. Physics 2 lab report 7 focal length of lenses focal. Hence, the focal length of the given lens is 10 cm. To find the focal length of a convex lens by plotting graphs between u and v or. In this experiment you will measure, as precisely as you can, the focal length of a lens. A lens with a focal length shorter than normal is often referred to as a wideangle lens typically 35 mm and less, for 35 mmformat cameras, while a lens significantly longer than normal may be referred to as a telephoto lens typically 85 mm and more, for 35 mmformat cameras. Optics track, light source, view screen, ruler, and a convex and concave lens.
Image formation for a convex lens essential questions. Lab preparation the picture on the screen in a movie theater is called a real image. 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. Rays of light from an object very far away from a thin lens will be approximately parallel when they reach the lens. The data of focal length of lens taken are recorded in the. Technically, long focal length lenses are only telephoto if the focal length is longer than the. Send both photos to yourself via email for analysis at microsoft paint. An equi convex lens of radius of curvature r is cut into two equal parts by a vertical plane, so it becomes a plano convex lens. Lenses convex converging lens laws of refraction and reflection can be used to explain how lenses and mirrors operate parallel rays e.
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