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3rd Preliminary Examination, 2018-19 Physics (2 hour) Grade: X Max Marks: 80 _____________________________________________________________________ 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. _____________________________________________________________________ Attempt all questions from Section A and any two questions from Section B. All working, including rough work, must be clearly shown and must be done on the same sheet as the rest of the answer. Omission of essential working will result in loss of marks. The intended marks for questions or parts of questions are given in brackets [ ]. _____________________________________________________________________ Section A (40 marks) (Attempt all questions from this section) Question 1 a) When a body is thrown vertically upward, its velocity keeps on [2] decreasing. What happens to its kinetic energy when its velocity b) becomes zero? A person can open a nut by applying a force of 120 N by using a lever [2] handle of length 40 cm. What should be the length of handle if he is able c) d) to open if he is able to open it by applying a force of 30N? Two bodies of masses m1 and m2 have equal kinetic energies. What will [2] be the ratio of their momenta? What is the work done in the following cases? (i) When moon makes a [2] complete revolution around the earth? (ii) A coolie carrying a load on his e) Question 2 a) head and walks on a level road. Define the term power. State it s SI unit. [2] Under what condition will a machine act as a (i) force multiplier (ii) [2] b) speed multiplier? What is the relation between MA and VR in (i) an ideal machine (ii) a [2] c) practical machine? Give one use each of the following (i) ultraviolet radiations (ii) infrared [2] d) radiations. Arrange the electromagnetic spectrum beyond red in their increasing [2] e) Question 3 a) b) c) d) e) Question 4 a) order of wavelength. Name the waves used in (i) SONAR (ii) RADAR State the factor that determine (i) pitch and (ii) quality of a sound. Write two conditions for an echo to be heard. State Ohm s law. Why the earth pin in a three in plug is always made thicker and longer? Distinguish between e.m.f. and terminal voltage. [2] [2] [2] [2] [2] [2] It is generally colder after a hailstorm than during and before hail storm. [2] b) Give reason. State the basic principle of heat transfer. Does it obey the law of [2] c) conservation of energy. What is electromagnetic induction? Name one device that works on this [2] d) principle. A radioactive substance is oxidized. What change would you expect to [2] take palce in the nature of its radio activity? Give reason for your answer. State two properties of alpha particles. e) [2] SECTION B (40 Marks) (Answer any FOUR questions in this section) Question 5 a) b) c) d) Where does the position of centre of gravity lie in (i) a cylinder (ii) triangular lamina. Obtain the expression for the potential energy of a body. Distinguish between work and power. Name the form of energy which a body may possess even when it is not [2] e) in motion. The following diagram shows an arrangement of 4 pulleys. A load L is [3] [2] [2] [1] attached to the lower block. Copy the diagram and i) Show the string around the pulleys. ii) Draw arrows to indicate tension in each part of the string. iii) Calculate the MA of the system. Question 6 a) Draw a ray diagam to show how can a prism deviate a ray through 1800. [4] b) Write two differences bewteen reflection by a plane mirror and total [3] c) d) internal reflection. Define dispersion of light. Which colour deviates the least? The power of a lens is -5.0 D. [3] i) What does the ve sign indicate? ii) What does the letter D indicate? iii) What is the focal length of this lens? Question 7 a) [2] c) i) State the condition for resonance to occur. ii) Why do we hear a loud sound in acoustic resonance? What energy change takes place in i) An electromagnet ii) An electric toaster? How musical sound differ from noise? d) What are mechanical waves? Give one example. [2] e) The same musical note when played on a piano and on a flute sounds [2] b) [2] [2] different. Why? Question 8 a) An appliance is rated 1500 W, 250 V. This appliance is connected to 250 [3] V mains. Calculate i) the current drawn. ii) the electrical energy consumedis 60 hrs. iii) the cost of electrical energy cousumed at the rate of Rs.2.50 per b) kWh. What are ohmic conductors? Draw a graph to show the voltage-current relationship. [2] c) What is an electric fuse? Name the material of electric fuse. [2] d) After referring the adjoining figure. [3] i) Obtain an expression for the effective resistance between A and B. ii) Calculate the value of effective resistance, if r = 2 . Question 9 a) 250 g of water at 30 0C is present in a copper vessel of mass 50 g. [3] Calculate the mass of ice requires to bring down the temperature of the vessel and its contents to 5 0C. [SHC of water = 4200 J/kg/K, SHC of b) copper = 400 J/kg/K and Latent heat of fusion of ice = 336 x 103 J/kg] Why water is used in hot water bottles for fomentation? [2] c) Is it possible to freeze water into ice by adding ice at 0 0C? Give reason [3] d) for your answer. What do you mean by latent heat? State its SI unit. [2] Draw a rough sketch of pattern of the field line due to [3] Question 10 a) b) i) current flowing through a circular coil. ii) current flowing through a solenoid. From the adjoining diagram, state the polarity formed at [2] A and B. c) Nucleus of an element ZXA emits an alpha particle and then a beta [2] d) particle. The final nuclear is ayb. Find a and b. What is nuclear fusion? Give two examples of fusion reaction. ***************************** [3]
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