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Physics preboard examination(2020-21) Class 10 ICSE 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 an Section I is compulsory. Attempt any four questions from Section II. The intended marks for questions or parts of questions are given in bracke SECTION I (40 marks) Attempt all questions from this Section. Question 1 (a) State the energy changes in the following cases while in use: [2] (i) a photovoltaic cell (ii) A ceiling fan [2] (b) Calculate the change in the Kinetic energy of a moving body if its velocity is reduced to 1/3rd of the initial velocity? (c) Can the centre of the gravity of a body be outside it? Justify [2] your answer giving an example (d) State the dependence of angle of deviation: [2] (i) On the refractive index of the material of the prism. (ii) On the wavelength of light. (e) Define the term velocity ratio. State its SI unit [2] Question 2 (a)Calculate the heat gained by 400g water when it is heated [ 2] from 10 C to 50 C. (Specific heat capacity of water = 4200 J / kg 0C) (b) Which physical quantity does the electron volt measure? How [2] is it related to the SI unit of this quantity? 1 (c) Name the region just beyond [2] (i) The red end (ii) The violet end ,of the spectrum (d) An electric kettle is rated 3kW,250 V. Give reason whether this[2] kettle can be used in a circuit which contains a fuse of current rating 13 A. (e) (i) Name the device used to protect the electric circuits from [2] overloading and short circuits (ii) On which effect of electric current does the above device work? Question 3 (a) (i) Name the characteristic of sound which enables a person to [2] differentiate between two sounds with equal loudness but having different frequencies. (ii) Name the characteristic of sound which enables a person to differentiate between two sounds of the same loudness and frequency but produced by different instruments. (b) (i) A ray of light passes from water to air. How does the [2] speed of light change? (ii) Which colour of light travels fastest in any medium except air? each other (c ) Arrange , and rays in ascending order with respect to [2] (i)Penetrating power (ii) ionizing power [2] (d) Give two reasons why the efficiency of a single movable pulley system is not 100% 2 (e) State any two precautions to be taken while handling radioactive substances. [2] Question 4 (a) (i) Give one example of motion in which speed remains [2] uniform but velocity changes . (ii) What is the position of the centre of gravity of a cylinder. (b) A metal wire of resistance 6 is stretched so that its [2] length is increased to twice its original length. Calculate its new resistance. (c )The refractive index of a material is 1.33. If the velocity of [2] light in vacuum is 3 x 108 ms-1, find the velocity of light in the material. (d) Give one example each where high specific heat capacity of [2] water is used i) in cooling ii) as heat reservoir. (e) State the position of the object in front of the converging lens if: (i) It produces a real and same size image of object. (ii) It is used as magnifying glass [2] Section II (Attempt any four questions from this section) Question 5 (a) (i) Complete the following [3] 1 J = erg (ii) A woman draws water from a well using a fixed pulley. The mass of bucket and water together is 6 kg. The force applied by the woman is 70 N. Calculate the mechanical advantage. (Take g = 10 m s ) 3 (b) A half meter ruler is suspended by a thread from [3] the midpoint of the ruler as shown in the fig. It balances horizontally when a 50 gm and an unknown weight w are suspended respectively from 10 cm and the 45 cm mark. Calculate the magnitude of weight w in kgf. (c ) The following diagram shows a pulley arrangement. [4] (i) In the diagram, mark the direction of tension on each strand of string. (ii) What is the purpose of the pulley B? (iii) If the tension is T, deduce the relation between T and E. (iv) What is the velocity ratio of the arrangement? Question 6. [4] (a) One isotope of uranium has a mass number 235 and atomic number 92. (i) What is the number of electrons in the neutral atom of this isotope 4 (ii) What is the number of protons and number of neutrons in its nucleus? (iii) Do all isotopes have the same number of neutrons? (iv) What is the number of protons and neutrons in U = ? (b) A slab of ice at 0 C is constantly heated till the [3] steam is formed at 100 C. Draw a graph showing the change in temperature with time. Label the various parts of the graph properly. [3] (c) A bucket contains 8kg of water at 25 c. 2kg of water at 80 c is poured into it. Neglecting the heat absorbed by the bucket, calculate the final temperature of the water. Question 7 [3] (a) How is the angle of emergence related to the angle of incidence when prism is in the position of minimum deviation? Illustrate your answer with the help of a labelled diagram using an equilateral prism. (b) A convex lens forms an image 16.0 cm long of an object 4.0 kept at a distance 6 cm from the lens. The object and the [3] image are on the same side of lens. (i) What is the nature of image ? (ii) Find the position of image and the focal length of lens. [4] (c ) Give one use each of (i) microwaves, (ii) ultraviolet radiations, (iii) infrared radiations, and (iv) gamma rays. Question 8. [3] (a) A radar is able to detect the reflected waves from an enemy airplane, after a time interval of 0.02 milliseconds. If 5 the velocity of the waves is 3 10 ms , calculate the distance of the plane from the radar. [3 ] (b) (i) Write the necessary condition for hearing an echo. (ii)What is meant by the terms: amplitude and frequency of a wave? [4] (c ) (i) State one advantage and disadvantage of the resonance of sound waves. (ii) What are the factors that affect the frequency of a vibrating string and how do they affect the frequency ? Question 9. [3] (a) (i) With reference to their direction of action, how does a centripetal force differ from a centrifugal force ? (ii) State the Principle of conservation of energy. (iii) Name the form of energy which a body may possess even when it is not in motion. (b) A body of mass 50 kg has a momentum of 3000 kgms-1. [3] Calculate : (i) the kinetic energy of the body. (ii) the velocity of the body. [4] (c) The following figure shows two ways (a) and (b) of connecting the three lamps A, B and C to a.c. supply of 220 V. Name the two arrangements. Which of them would you prefer in a household circuit? Give reason for your answer. 6 Question 10 [3] (a) The diagram shows a three-pin socket marked as 1,2 and 3 Identify and write live (L), neutral (N) and earth (E) against the correct number. (i) To which part of the appliance is the terminal 1 connected ? (ii)To which wire joined to 2 or 3, is the fuse connected and why ? [3] (b) State three differences between e.m.f. and terminal voltage of a cell. [4] (c ) (i) Two bulbs are marked 100 W, 220 V and 60W, 110V. Calculate the ratio of their resistances. (ii) Calculate the equivalent resistances between A and B from the following diagram. 7 --------------------------------------------------------------------- 8
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