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PHYSICS PAPER 2 (PRACTICAL) Answer all questions. You should not spend more than one and a half hours on each question. Question 1 [12] This experiment determines the focal length of the given convex lens by displacement method. You are provided with: (a) A lens holder (b) A convex lens (c) Two optical pins (d) An optical bench Note: The experiment may be performed on a table top, using a metre scale, in case an optical bench is not available. (i) (ii) Determine the approximate focal length f of the given convex lens by projecting the image of a distant object on a wall or a screen. Record the value of f in cm, correct upto one decimal place. Now, arrange the object pin O, the image pin I and the lens L on the optical bench or table top as shown in Figure 1(a) so that the tips of O and I lie on the principal axis of the lens. I L O x Figure 1(a) (iii) (iv) (v) L1 Adjust the distance x between O and I to be nearly equal to (4f + 10) cm. Ensure that this separation is maintained throughout this particular setting. Move the lens towards the pin I and adjust its position until the diminished and inverted image of O coincides with the image pin I. Read and record the positions of O, L1 and I on the metre scale in cm, correct upto one decimal place. 30
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