Lens Experiment - Stony Brook University 1/F = 1/f 1 + 1/f 2. Apparatus and other necessary materials: Optical bench, Experimental convex leas . An object is placed at a point beyond the focus of lens L1. Now, to obtain the focal length of the combination lens, we have the following: F = (uv)/ (u + v) cm. When the lenses of individual focal lengths f c and f D, are placed in contact, the effective focal length f of the combination is given by: Equation 1. Note : above two conditions are valid if one lens is convex and the other is concave . Graphically and algebraically determining the nature of image formed in a convex, a concave and combined lenses using thin lens equation and ray diagram is the main objective of the experiment. 1.4 Summary of Thin Lenses Theory - Combination of Lenses and Power When two thin lenses, of focal lengths f 1 and f2, are put close together, the combination acts like a single lens of focal length f, given by 1 f 1 f 1 1 f 2 (4) In Equation 4, all focal lengths are signed quantities. s is assumed to be extremely large, allowing us to treat 1/s≈0 which leaves f≈s' In our experiment do is the distance from the Earth to the Sun (1.50 x 10 11 m), di the lens to screen distance, ho is the size or diameter of the Sun (1.39 x 10 9 m) and hi is the spot size. 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. Focal length of the convex lens should be less than the focal length of concave lens so that the combination is convex. (b) The device X is a concave mirror of focal length 40 cm. Experiment No. Contents: Lens I focal length f 1 = Lens II focal length f 2 = Object Distance d o (cm) Measured Image Distance d i (cm) Calculated . This parallel beam can be further used to carry out the combination-of-lens method. Lenses 1. The lens used above is convex and the focal length is positive. The formula for focal length is as follows: 1/f = 1/s' + 1/s. 6 Object: To verify the expression for the focal length of a combination of two lenses. You can perform the actual experiment in 3D LabInApp Physics software ( http://www.. A diverging lens with the magnitude of focal length 25 cm is placed . Focal Lengths of Simple Lenses There are six sections in this lab. 3. Find the focal length of the combination. However, when a diverging lens is used in combination with a converging lens, for instance, the object can be virtual, the image real. (d) The device X is a convex lens of focal length 40 cm. [On R.H.S] Combination of lenses Aim: To obtain a lens combination with the specified focal length by using two lenses from the given set of lenses. Power of a lens, P = 100/ƒ (cm) Diopter (D) or 1/ƒ. 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. Experiment: Determine the focal length of a concave lens by combining it with a suitable convex lens. Mount the convex lens Lt such that the object distance SL1 . Use the optical bench 1. AIM: To determine the focal length of converging lens and it's radius of curvature. 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: Centre of curvature: 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. A parallel light beam is produced with the lamp and the double condenser. Table-1 Lens Screen Position Lens Position Af cm cm cm А 0 10.2 0.3 0 B E 4.1 0 20.1 0.3 0.3 Lens combinations: Table-2 Lens Screen Combination Position cm Lens Position -- f12 f cm 0 E&D E&C 0 5.5 7.5 20.5 A&D 0 For fi use the focal lengths you got in the table-1 Show calculations for f: I , why v2=u1 and v1=u2? Apparatus: A set of thin convex lenses, A single lens holder, A lens holder which can hold two lenses touching each other, A metre rod and a screen. This is demo video of experiment to find the focal length of convex lens. So, if the focal length of a lens is known the power of that lens can be determined by the following equation. Two converging lenses of equal focal length 'f' are placed in contact. Asked by narendra172193 9th April 2021 3:27 PM . To accomplish this, a real image from a converging lens will . Now, power of the combination of the two lens is +12D-2D (+10D) As we know that power = 1/ focal length +10=1/ focal length focal length =0.1m= 10cm. Click hereto get an answer to your question ️ Two identical glass (mug = 3/2) equiconvex lenses of focal length f are kept in contact. `45cm`and90cm C. `15cm`and35cm D. `30cm`and-45cm 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. This forms the combination of lenses. Method (1). As d tends to zero, the value of the BFL tends to the value of f given for thin lenses in contact. where, f1, and f2 are the focal length of lens-1 and lens-2 respectively and d refers to the distance between the two lenses. A concave lens has a negative focal length. asked Aug 28, 2019 in Science by navnit40 Expert ( 40.4k points) optics 3. Experiments to measure the focal length of a converging lens. experiment lens march 24, 2016 callais purpose the purpose of the experiment is to validate the lens The lenses must be clean. Stack Exchange Network. . Note: The lens position is taken from the center of the length, which is assumed to be half the total thickness of the lens. As we know, the equivalent focal length of the combination of two lenses in contact is given by the relation. The lens is measured at 10.5 mm, therefore 5.25 mm was added to the original measurement where the fiducial mark indicates. Visualizing a virtual image is possible but dicult. If two lenses of fecal lengths f 1 and f 2 are kept in contact, the focal length F of the combination is given by. When a concave lens of focal length f 2 is placed coaxially in contact with a convex lens of focal length f1 and if F is the focal length of the combination, then, Therefore, the focal length of the concave lens, b) Lens out of contact method. B y . The lensmaker's equation for thin spherical lenses may be written in the form 11. Goal:!!To!determine!the!focal!length!of!a!concave!lens!and!to!better!understand!how! If f 2 > f 1 the combined lens behaved as a convex lens. (You may want to darken the room before starting.) Theory: 1. hope it help. Repeat the measurement by adjusting the distance between lamp-housing and the screen (s) to roughly about 5.4F, 5.8F, 6.2F and 6.6F. In other words: xo = s1 +f1 (4a) xi = f2 +s02 (4b) where f1 and f2 are the distances between the focal points and . My detailed lab reports from Physics 2 Lab with Dr. Sorci. Theory: 1. A convex lens of focal length `25 cm` is placed co-axially in contact with a concave lens of focal length `20 cm`. 1 u where w is the distance . 2. www.citycollegiate.com. Galilean telescope: Use the negative focal-length lens (\(f\) = −25 mm) as the eye lens and the +100 mm or +200 mm lens as the objective, and focus a distant object. = 1 푓 푓 = 11. lies between ft and 2f 1, where ft is the approximate focal length of the convex lens. Radius of curvature: For a curved mirror, the radius of curvature, R can be defined as the radius of . 130 Experiment 22: Thin Lenses PART 2: Diverging Lens To determine the focal length of a diverging lens, the lens must create a measurable, real image as in Part 1. comparing equation (3) and equation (4) , we get. We use the lens formula in this experiment to calculate the focal length of the concave lens: f = uv u−v f = u v u − v. Where, f is the focal length of the concave lens L1. Two thin lenses of focal length f1 and f2 are coaxially placed in contact with each other then the power of combination is _____ . It is placed between the illuminated wire gauze and the screen at a fixed distance away from the wire gauze. From this formula, we get the way to find the focal length of a convex lens/find focal length of convex lens. 2 The place where the five refracted rays cross each other is the focal point of the lens. Determination of the focal length of an unknown convex lens by using thin lens Lab report on physics experiment 9 experiment thin spherical lenses lab report name: tiisetso khumalo 1914276 date: introduction: what is the experiment about? to!locate!images!for!lens!combinations . Answered by Expert CBSE X Physics Electricity This is the question from class 10 light chapter asked in our state model paper . . 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. 4. At the second part of the experiment the equivalent focal length of the two-lens system has been calculated with the help of different individual test lenses. Whereas, Concave lens has a focal length of -10cm or -0.1m. Two thin lenses separated by some distance : If two thin lenses are held a distance d apart from each other, then focal length of the combination is given by the relation, 1/F = 1/f 1 + 1/f 2 - d/f 1 f 2 Practice Problems : 1. 3. For combinations of two thin lenses in contact, we have seen that the focal length of the combi-nation is given by an expression involving the individual focal lengths: 1 f = 1 f1 + 1 f2 (4) Combinations of two thin lenses can be used to make an extremely important optical device: the refracting telescope. The power of a lens is given by the equation: Equation 2. The focal lengths of a biconvex lens and a concave mirror are shown in Figures 1 and 2, respectively. u is the distance of I from the optical centre of the lens L2. Apparatus Required: Two convex lenses of different focal length and an optical bench with four uprights; a lamp of narrow opening, a cross‐slit screen, nodal slide assembly and a plane mirror. and the separation d is adjustable between 0 and 4.0 cm, find the maximum and minimum focal lengths of the combination. . The image formed is virtual. Created Date: 7/21/2008 7:43:23 PM . 13~8) near one end of the optical bench. Use the lens maker's equation, 1 푓= 1 푢+ 1 푣 , to justify this method. Conclusion The objective of this experiment is to determine the focal length of a convex lens using different locations of the object and graphical method. Figure 3: Experimental set-up for determining the focal length of a lens. From (3) we see that if an object is upright then the image we see from the lens will be inverted. Consider Eq. Note that in Step 2, the rays leaving the lens are diverging and they will not cross. EXPERIMENT 2. [1 mark] Focal pole-the point on the other side of the length where rays meet/converge. Other precautions are same as given in Experiment 3. If the separation distance is equal to the sum of the focal lengths (d = f1+f2), the combined focal length and BFL are infinite. The experiment is set up as shown in Fig. This forms the combination of lenses. The focal length of the combination is -10 cm. B. `30cm and 60cm` B. The total power of these two lenses is given by the equation: P tot = P c + P D Equation 3. . Answer (1 of 3): you have a combination of concave and convex lens both have a focal length of 10 cm . Use the data sheet provided to record focal lengths. If f 1 >f 2 the combined lens behaves as a concave lens. Apparatus: A set of thin convex lenses, A single lens holder, A lens holder which can hold two lenses touching each other, A metre rod and a screen. The focal length (F) of a combination of two convergent lenses using Nodal Slide Assembly is given by: 1/ F =1/ f1 + 1 / f2- d / f1 f2. Determine the power of the combinat asked Jun 11, 2019 in Physics by JaishankarSahu ( 85.2k points) If the light source is placed at the focal point, a convex lens will give parallel beam as output. Power of a lens, P = 100/ƒ (cm) Diopter (D) or 1/ƒ. If the separation distance is equal to the sum of the focal lengths (d = f1+f2), the combined focal length and BFL are infinite. or, P = 1/ƒ (cm) Diopter (D). Concave(Lensesand(LensCombinations(! The distance from the second lens to the focal point of the combined lenses is called the back focal length (BFL). As d tends to zero, the value of the BFL tends to the value of f given for thin lenses in contact. The expression for the focal length of convex lens Lt such that the object distance SL1 two conditions are if! 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