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First Preliminary Examination 2020-2021 Physics Grade: 10 Date: 16/12/20 Max. Marks:80 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 questions from Section I. Attempt any four questions from Section II. SECTION I (40 marks) Attempt all the questions from this section Question 1 a. What do you understand by moment of force? Give one way to obtain a greater moment of force about a given axis of rotation. b. A boy weighing 50kgf climbs up a stair of 20 steps each 20cm high in 4min and a girl weighing 30 kgf does the same in 2min ,compare (i) The work done by them and (ii) The power developed by them . c. Explain the term Mechanical Advantage. Why M.A V .R for an actual machine. d. What do you mean by the following statement ? (i) The heat capacity of a body is 50 J K 1 ? (ii)The specific heat capacity of copper is 0.4 J g 1 k 1 ? e. A metal piece of mass 50g at 270 C requires 2400 J of heat energy in order to raise its temperature to 3270 C . Calculate the specific heat capacity of the metal. [2] [2] [2] [2] [2] Question 2 a. i) State the effect of presence of impurity on the melting point of ice. ii) State the effect of increase of pressure on the melting point of ice. b. An electromagnetic radiation is used for photography in fog i) Identify the radiation. ii) Why is this radiation mentioned by you ideal for this purpose? 1 [2] [2] c. Copy the diagram given alongside and complete the path of light ray till it emerges out of the prism . the critical angle of glass is 420 . In your diagram mark the angles wherever necessary. d. When does a ray of light passing through a rectangular glass slab does not suffer refraction? What is the angle of incidence in such a situation? e. What is meant by an echo? State one condition necessary for an echo to be heard distinctly. Question 3 a. What is the work done by a force when the force is: i) normal to the displacement produced. ii) in the same direction as the displacement produced. b. The human ear can detect sound in the frequency range 20 Hz to 20,000 Hz. If the speed of sound is 330 m/s, find the wavelength, corresponding to the audible range of frequencies . c. An electric bulb is rated 220V, 100 W . i) What is its resistance ? ii) What safe current can be passed through it? d. Name two examples in which the mechanical energy of a system remains constant. e. The V against I graph for a series and parallel combination of two resistors is shown in the figure below. Which of two : A or B, represents the parallel combination? Give a reason for your answer. 2 [2] [2] [2] [2] [2] [2] [2] [2] Question 4 a. What do you mean by background radiations? Is it possible for us to keep ourselves away from it ? b. During emission , how the following change: i) The mass number of radioactive elements? ii) Atomic number of radioactive elements? c. Calculate the value of X if the total resistance across AB is 3.2 . [2] [2] [2] d. (i) What do you understand by the change of phase of a substance ? (ii) Does the substance absorb or liberate any heat energy during the changes of phase? [2] e. A body of mass 60 Kg has momentum 3000kg m/s .Calculate : i) Kinetic Energy ii) the speed of the body. [2] SECTION II (40 marks) Attempt any four questions from this section Question 5 a. i) State the principle of moments. ii) A force of 5 N applied at the edge of a door produces a moment of force of 4.5Nm. What is the width of the door? [3] b. A uniform meter rule is balanced at 40 cm mark, when weights of 25gf and 10 gf are suspended at 5cm and 75cm mark respectively. Calculate weight of the meter rule. [3] c. i) What do you understand by the term power? ii) Give one difference between Energy and Power. iii) The power of an electric motor is 5kW . At what speed it can raise a load of 25000N ? [4] 3 Question 6 a. I. Give three Distinguishing points between heat capacity and specific heat capacity. ii. Write relation between heat capacity and specific heat capacity. b. i) What is the principle of method of mixture? ii) What is the other name given to it? iii) Name the law on which the principle is based. c. 45 g of water at 500 C in a beaker is cooled when 50 g of copper at 180 C is added to it. The contents are stirred till a final constant temperature is reached. Calculate the final temperature. The specific heat capacity of copper is 0.39 J g 1 K 1 and that of water is 4.2J g 1 K 1 . Question 7 a. Name the three factors on which the deviation produced by prism depends and state how it depends on the factors stated by you. b. State the factors on which the shift by which the object appears to be raised depend. c. Give one property of each of the electromagnetic radiations given below. i. Microwave ii. X-rays iii. Infrared radiation iv. Gamma rays Question 8 a. i. State Ohm s law. ii. A metal wire of resistance 6 is stretched, so that its length is increased to twice its original length.calculate its new resistance. b. A cell of emf 1,5 V and internal resistance 1.0 are connected to two resistors of 4.0 and 20.0 in series as shown in the figure. Calculate: I. Current in the circuit. II. Potential difference across the 4.0 resistor. III. Voltage drop across internal resistance when the current is flowing. IV. Potential difference across the cell. 4 [4] [3] [3] [3] [3] [4] [3] [4] c. i. Why is it necessary to have an earth wire installed in a power circuit. ii. What are the characteristics properties of fuse wire? iii. Name the safety device which are connected to the live wire of a household electric circuit. Question 9 a. A man stands in between two parallel cliffs and fires a gun. He hears the first echo after 0.8 s and the second echo after 2.5s. Calculate the distance between the cliffs. b. i. What are damped vibrations? ii. Give one example of damped vibration. iii. Name the phenomenon that causes a loud sound when the stem of the vibrating tuning fork is kept pressed on the surface of a table. c. i. State two important properties of ultrasonic waves which are useful in SONAR. ii. A SONAR signal of frequency 1X 106 Hz has wavelength 1.5 X 10 3 m in [3] [3] [3] [4] water.What is the speed of the signal in water? Question 10 a. i. When does the nucleus of an atom become radioactive? ii. How is the radioactivity of an element affected when it undergoes a chemical change to form a chemical compound? iii. Mention one Harmful effect of radioactivity. [3] b. i. Compare ionising power of , and r adiations. ii. Give Three common properties of particles and cathode rays. [4] c. What happens to the position of an element in the periodic table when its nucleus emits : i. an particle ii. A particle iii. radiations. [3] ****** 5
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