NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY, GREATER NOIDA Experiment No: 1 NODAL SLIDE 1.1 Objective 1.2 Apparatus required 1.3 Theory 1.4 Diagram 1.5 Ray Diagram 1.6 Procedure 1.7 Observation table 1.8 Calculations 1.9 Result 1.9 Precautions and Sources of error 1.11 Viva - Voce 1.1OBJECTIVE: To determine the focal length combination of two lenses separated by a distance with the help of a nodal slide and to verify the formula: 1 1 1 x F f1 f 2 f1 f 2 Where, F = Focal length of the combination. f1, f₂ = Focal lengths of the given lenses, x = Separation of the two lenses. 1.2 APPARATUS REQUIRED: Nodal slide, Optical Bench, Two Plano convex lens, Plane mirror, Cross slit, a lamp etc. 1.3 THEORY AND FORMULA USED: In a coaxial optical system of two thin convergent lenses, the medium on either side of the lenses and also between them is air, therefore nodal points coincides with the principal points. Hence such an optical system has four cardinal’s points (i) Two principal points (h 1, h2) or nodal points (n1, n2) and (ii) Two focal points (f1, f2) 1. The distance of the first principal point h1 from the first lens L1 is given. 2. The distance of the second principal point h 1 from the second lenses L1 is given Focal length (F) of combination of two lenses separated by a distance x is given by: 1 1 1 x F f1 f 2 f1 f 2 Where, f1, f₂ = focal lengths of the given lenses (L1 & L₂) respectively. Department of Physics, Engineering Physics Lab Page 142 NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY. GREATER NOIDA 1.4 DIAGRAM: 1.5 Ray Diagram: Department of Physics. Engineering Physics Lab Page 143 . Engineering Physics Lab Page 144 . f. 3. The lens is now rotated slightly about the verticals axis which shifts the position of image either towards the left or right but no shift of the image is obtained by moving the carriage carrying the lenses axially. cm. are mounted on upright of the optical bench and the heights of uprights are adjusted in such a manner that the line joining the centers of each part is parallel to the bed of the bench. Now rotate the carriage on its upright by a few degrees and if there is a shift of the image. This distance gives the combined focal length of two lenses.7 OBSERVATION TABLE: Table for focal length of lenses L1 and L2 Lens Lı S. No. This gives the distance between two lenses. the source of light. After this distance between two lenses and find out the combined focal lengths. Note down the position of this uprights carrying the cross slit and nodal slide assembly on the optical bench. d. c. Lens L₂ Position of cross slit (a) Position of lens (b) cm. the cross slits are in the focal plane of the lens. In the solution. Mean fı = (a-b) fı cm. The image may be blurred but will defined image is formed by moving the upright of nodal slid away or toward the cross slits. Illuminate the cross slit and adjusts the plane of the plane mirror to get image of cross slit very near to it. One face Other face One face Other face Table for focal length of the combination of lenses L1 and L2 Department of Physics. g. h. GREATER NOIDA 1. One face Other face 2. One of the lenses L1.6 PROCEDURE: a. Mean f₂ = (a– b) f₂ c m. The distance between cross slits gives the focal length of the lens. Position of lens (b) cm. Light incident Position of cross slit (a) cm. Rotate the lens system by 180⁰ and repeat above procedure. Remove the first lens and mount the second lens on the upright. move the carriage on its upright by means of rack and pinion arrangement till there is no shift. Move the upright carrying the lenses toward or away from the cross to obtain a sharp and most intense defined image. 1. cm. As described above find the focal length of the second lens. Mount both the convex lenses on the nodal slid arrangement and note down their positions. b.NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY. e. cross slit and mirror. cm. 1. No. It is used to determine the nodal points of a lens system. Distance between lens Position of cross slit Position of nodal slid upright (a) (b) F = (a–b) (c) Calculated value of F (d) Difference (c-d) 1. e. slits. 1. Slit should be well illuminated.9 RESULT: The calculated and experimentally observed value of the focal length of the combination are very nearly equal and hence the formula 1 1 1 x F f1 f 2 f1 f 2 is verified.2. 1.8 CALCULATION: Calculate the combined focal length with the help of the formula: 1 1 1 x F f1 f 2 f1 f 2 1. Qu. Bench error should be determined. No image shift position should be obtained accurately. b.10 PRECAUTIONS AND SOURCE OF ERRORS: a. nodal slid arrangement and plane mirror should be rotated about a vertical axis by few degrees.1. 3. 2. c.NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY. 1. Source. The mirror should be truly plane. What are nodal points? Department of Physics. f. Why do you call it nodal slide? Ans. The carriage caring the nodal slid arrangement should be rotated about a vertical axis by degree d. Engineering Physics Lab Page 145 . GREATER NOIDA S.11VIVA – VOCE: Qu. Video link. https://www.3. How will you make sure that the image used by you is the desired one? Ans. Thus the principle is based on the property of nodal points. No Qu.NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY. Qu. If by rotation of plane mirror the image moves on the screen then it is the desired image otherwise not. Qu.com/watch?v=KLPCfxMb7WQ Department of Physics. Engineering Physics Lab Page 146 . the image does not shift laterally when the system is rotated about a vertical axis passing through its second nodal points. Qu. What is the principle of this method? Ans. Nodal points are a pair of conjugate points having unit positive angular magnification. Is it necessary to rotate the lens combination by 1800? Ans. because the two nodal points are not symmetrical with respect to two lenses.youtube. Will the position of the desired image be affected in any way by alternating the position of plane mirror? Ans.4.5.6. It is not necessary if the focal length is same for the two lenses. Yes. If a parallel beam of light is incident on a converging lens system thus forming an image on a screen in its second focal plane. GREATER NOIDA Ans.