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VIBGYOR HIGH Second Preliminary Examination AY 2020-2021 PHYSICS Grade: X Max. Marks: 80 Date: 11/01/2021 Time Allowed: 2 Hours INSTRUCTIONS: Answers to this paper must be written on the paper provided separately. You will not be allowed to write during the first 15 minutes. This time is to be spent in reading the question paper. The time given at the head of this paper is the time allowed for writing the answers. The intended marks for the questions or parts of questions are given alongside the questions. Attempt all the questions from section I and any four questions from section II. Section I (40 Marks) Attempt all questions from this section Q1 Answer the following questions: [10] a. A wheel of diameter 2 m is shown with axle at O . A force F = 2 N is applied at B in the direction shown in the figure. Calculate the moment of force about: (i) the centre O, and (ii) the point A. 1 [2] b. The power of a motor is 40 KW. At what speed can the motor raise a load [2] of 20,000 N? c. How is mechanical advantage related with the velocity ratio for an actual [2] machine? State whether the efficiency of such a machine is equal to 1, less than 1 or more than 1. d. An electromagnetic wave has a frequency of 500 MHz and wavelength of [2] 60 cm. (i) Calculate the velocity of the wave. (ii) Name the medium through which it is travelling. e. A pendulum has a frequency of 5 vibrations per second. An observer [2] starts the pendulum and fires a gun simultaneously. He hears an echo from the cliff after 8 vibrations of the pendulum. If the velocity of sound in air is 340 ms-1, find the distance between the cliff and the observer. Q2 Answer the following questions: [10] a. Define the term centre of gravity . What is the position of centre of gravity [2] of: (i) solid cone and (ii) rectangular lamina? b. Define the term potential energy of a body. Name its two forms. [2] c. [2] State any two differences between a single fixed pulley and a single movable pulley. d. Calculate the minimum distance in air required between the source and [2] the obstacle to hear an echo. Take the speed of sound in air = 350 ms -1. e. What is meant by natural frequency of vibration of a body? State one [2] factor on which it depends? Q3 Answer the following questions: [10] 2 a. How fast should a man weighing 600 N run so that the kinetic energy is [2] 750 J? (Take g = 10 ms-2). b. Draw a diagram to illustrate the total internal reflection. [2] c. [2] State difference between a convex and a concave lens in their: (i) appearance and (ii) action on the incident light. d. Where must be an object placed in front of a convex lens of focal length [2] 20 cm to obtain a real and four times magnified image? e. (i) Define the term radioactivity . [2] (ii) How does the refractive index of a medium depend on the wavelength of light used? Q4 Answer the following questions: [10] a. What are isotones? Give one example. [2] b. A piece of iron of mass 2 kg has a thermal capacity of 966 JK-1. Find: [2] (i) heat energy required to warm it by 15 0C and (ii) its specific heat capacity in S.I. unit. c. Define the term power of a lens. In what unit is it expressed? d. Draw a ray diagram to show how a converging lens can form a real and [2] [2] enlarged image of an object. e. In what unit does the electric meter in a house measure the electrical [2] energy consumed? What is its value in S.I. unit? Section II (40 Marks) Attempt any four questions from this section Q5 Answer the following questions: [10] a. A uniform metre rule balances horizontally on a knife edge at the 58 cm [3] mark when a weight of 20 gf is suspended from one end. (i) Draw the diagram of the arrangement. (ii) What is the mass of the rule? b. A pump is used to lift 500 kg of water from a depth of 80 m in 10 s. Calculate: (i) The work done by the pump. 3 [3] (ii) The power at which the pump works. (iii) The power rating of the pump if its efficiency is 40%. (Take g = 10 ms-2) c. (i) Define the term specific heat capacity and state its S.I. unit. [4] (ii) An electric heater of power 600 W raises the temperature of 4 kg of a liquid from 10 to 15 0C in 100 s. Calculate: 1. The specific heat capacity of the liquid. 2. The heat capacity of 4.0 kg of liquid. Q6 Answer the following questions: [10] a. A block and tackle system has 5 pulleys. If an effort of 1000 N is needed [3] in the downward direction to raise a load of 4500 N, calculate: (i) The mechanical advantage, (ii) The velocity ratio and, (iii) The efficiency of the system. b. State three differences between heat and temperature [3] c. [4] In each of the following cases, where must an object be placed in front of a convex lens so that the image formed is: (i) At infinity (ii) Of same size as the object (iii) Inverted and enlarged (iv) Upright and enlarged. Q7 Answer the following questions: [10] a. Show with the aid of a ray diagram, how a right-angled isosceles prism [3] can be used to invert the rays. Which phenomenon is responsible for this action of prism? b. How do you tune your radio to a particular radio station? Name the [3] phenomenon involved in doing so. c. State two uses of each of the following: [4] (i) Ultraviolet radiations (ii) Infrared radiations Q8 Answer the following questions: a. [10] (i) What is a prism? [3] (ii) A coin kept inside water ( = 4/3), when viewed from air in a 4 vertical direction, appears to be raised by 2.0 mm. Find the depth of coin in water. b. Explain the meaning of e.m.f, terminal voltage and internal resistance of [3] a cell. c. (i) State Ohm s law. [4] (ii) A wire of 3 resistance and 10cm length is stretched to 30 cm length. Assuming that it has a uniform cross section, what will be its new resistance? Q9 Answer the following questions: [10] a. You have three resistors of values 2 , 3 and 5 . How will you join [3] them so that the total resistance is less than 1 ? Draw diagram and find the total resistance b. (i) Why is the fuse wire fitted in a porcelain casting? [3] (ii) How does the thickness and length of a fuse wire depend on its current rating? c. The diagram in Fig. shows a three-pin socket marked as 1, 2 and 3. [4] (i) Identify and write live (L), neutral (N) and earth (E) against the correct number. (ii) To which part of the appliance is the terminal 1 connected? (iii) To which wire joined to 2 or 3, is the fuse connected and why? Q 10 Answer the following questions: a. [10] (i) What do you mean by equilibrium of a body? [3] (ii) State the condition when the body is in: 1. static, 2. dynamic equilibrium. b. Name the machine for each of the following use: (i) To multiply force (ii) To change the point of application of force 5 [3] (iii) To change the direction of force c. (i) What kind of change takes place in the nucleus when a -particle is emitted? (ii) Express it by an equation. (iii) State whether atomic number and atomic mass number are conserved in a radioactive - decay. ***** 6 [4]
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