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Preliminary Examination 2021 PHYSICS Grade :X Maximum Marks: 80 Date: 2/02/2021 Time: 2 hours Instructions Answer to this paper should be written in separate answer sheets provided to you. You have two hours to answer this paper excluding the reading time. You will be given first 15 minutes as reading time. You are not supposed to write during these 15 minutes. All questions are compulsory in Section A (40 marks). Each question carries 10 marks. Marks allotted to each question is mentioned against it. In Section B (40 marks) you need to attempt ANY FOUR questions of your choice. Each question carries 10 marks. This paper consists of 6 printed pages. __________________________________________________________________ Section A (Answer all questions) Question 1 (i)Redraw the diagram given below and mark the point of application and the direction of force to turn it anticlockwise. [2] r r (ii) Page 1 of 6 If the radius of wheel is r then what will be the moment of force? Is it vector or scalar? [2] (iii) (a) A radioactive substance is oxidized. Will there be any change in its radioactivity? Give reason. [2] (b) An iron ball requires 6000 J of heat energy to raise the temperature by 200 C. Calculate the heat capacity of the iron ball. [2] (c) List two factors on which the critical angle depend on. [2] Question 2 (i) A lens has power of -2D. Name the lens and find its focal length. (ii) How does angle of deviation change for a given angle of incidence with change in (iii) (a) Refractive index of the material of the prism (b) Wavelength of color used. V-I graph for series and parallel combination is shown in the diagram given below. (a)Identify the graph for each combination. (b) What does slope of each graph provide? (iv) (v) changes to 12Mg24 as a result of radioactive emission. (a)Name the particle emitted during this emission. (b)Give reason for your answer. 11Na [2] [2] [2] 24 [2] (a)Locate the center of gravity of a circular ring. (b)Name a factor on which center of gravity depends on? [2] Question 3 (i) Page 2 of 6 Calculate the effective resistance across a and b in the circuit shown below. [2] (ii) State the energy conversion in the given device while in use. (a)electric iron (b)dry cell [2] A metal sphere of mass 200 g falls from a height of 5 m. Calculate the kinetic energy just before it strikes the ground. (g = 10 ms-2) [2] 0 Ice cream is colder than water at 0 C. Give reason. [2] Copy the diagram and complete the path of ray. [2] (iii) (iv) (v) Question 4 (i) (ii) (iii) (iv) A conducting wire is cut into 3 equal parts. How does resistivity of the conductor change? Give reason. [2] Name the wave used for sound navigation and ranging. Write one property of this wave which is used in this process. [2] A man spends a power of 2000 W to move a cart with force of 100 N. Find the velocity attained by the cart. [2] What is the use of a simple machine if (a)MA is greater than 1 (v) Page 3 of 6 (b)MA is equal to 1 [2] What are background radiations? Give one example. [2] SECTION B (Answer ANY FOUR questions) Question 5 (i) (ii) Give reason: (a)Fuse should be connected to live wire. (b)Thick wire has less resistance compared to thin wire of same length. [4] Compare free vibrations and forced vibrations.(3 points) [3] A uniform meter rule is balanced at 45 cm mark when a weight of 20 gf is suspended from one end. (a)Draw a suitable diagram for the arrangement. (b)Identify the clockwise moment. (c)Calculate the weight of meter scale. [3] Question 6 (i) A block A weighing 200 N is pulled up a slope of length 5 m by means of constant force of 200 N as shown in the diagram. 3m 5m A (a)Calculate the work done to move block A along the slope of 5m. (b)What is the increase in potential energy of the block? (c)Why is the work done different from increase in potential energy? (d)Is the work done positive and negative. (ii) (iii) [4] A stamp placed under a glass slab of refractive index 1.5 appears raised by 0.6cm. Find the real thickness of glass slab. [3] List three properties of electromagnetic waves. [3] Question 7 (i) (ii) A convex lens forms an erect and 3 times magnified image of an object placed at a distance of 10 cm in front of it. Find (a)the position of image (b)the focal length of the lens. [4] Give reason: (a)No work is done by a satellite revolving around a planet. (b)Shining of diamond. Page 4 of 6 (c)Infra-red radiations are used in sending signals during fog. (iii) [3] (a) State principle of calorimetry. (b)Two substances A and B have specific heat capacities 200 Jkg-1K-1 and 1850 Jkg-1K-1 respectively. Which one is a good conductor of heat. Give reason. [3] Question 8 (i) A certain sound has frequency of 256 Hz and wavelength of 1.3 m. (a)Calculate the speed with which the sound travels. (b)Compare the above speed if another sound travels at the same frequency of wavelength 2.6m. [4] (ii) Calculate the reading of the ammeter when (a) Key is closed (b) Key is open [3] (iii) Give reason: [3] (a)Nichrome is preferred in making heating element. (b)Metallic parts of electrical devices are earthed. (c)Soldiers are asked to break their steps while marching on a suspension bridge. Question 9 (i) What is lateral displacement? State three factors on which it depends. (ii) Give reason. [4] (a)Icecaps on mountains do not melt all at once. (b)Calorimeter is made of thin sheet of copper. (c)Water is used as good coolant. (iii) Page 5 of 6 Two pendulums are suspended as shown in the diagram.(next page) [3] When pendulum a is made to oscillate from mean position, after some time pendulum b also starts oscillating. (a)Name the oscillation executed by pendulum a (b)Name the oscillation executed by pendulum b (c)Name the phenomena which makes pendulum b oscillate. [3] Question 10 (i) (ii) An element z XA decays to 85R222 after emitting 2 alpha particles and one beta particle. Find the atomic number and mass number of X. Compare the ionization and penetration power of alpha and gamma particles. [4] In the diagram shown below name the radiations A, B and C. Write one application of radioactive isotope. [3] (iii) Give Reason: (a) People working with radioactive materials should wear lead lined gloves and aprons. (b) A person standing between two vertical cliffs, 800 m away from one of the cliffs shouts and hears first echo after 5 seconds and second echo 10 s later. Calculate (i)Speed of sound in air (ii)Distance between the cliffs. [3] ________________________________________________________ Page 6 of 6
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