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MADHUSTHALI VIDYAPEETH F.M 80 Time 2h Date : FIRST ASSESSMENT : 2019-2020 SUBJECT: PHYSICS CLASS- X SECTION A Attempt all questions from this section Question 1 a) State the energy changes in the following cases while in use: (i) An electric iron. (ii) A ceiling fan. b) The diagram below shows a lever in use: [2] [2] (i) To which class of levers does it belong? (ii) Without changing the dimensions of the lever, if the load is shifted towards the fulcrum what happens to the mechanical advantage of the lever? c) The power of a lens is - 5D. [2] (i) Find its focal length. (ii) Name the type of lens. d) (i) State the relation between the critical angle and the absolute refractive index of a medium. (ii) Which colour of light has a higher critical angle? Red light or Green light. [2] e) The following diagram shows a 60 , 30 , 90 glass prism of critical angle 42 , Copy the diagram and complete the path of incident ray AB emerging out of the prism marking the angle of incidence on each surface. [2] Question 2 a) (i) Why is the ratio of the velocities of light of wavelengths 4000 AO and 8000 AO in vacuum 1:1? (ii) Which of the above wavelengths has a higher frequency? [2] O b) A type of electromagnetic wave has wavelength 50A . (i) Name the wave. (ii) State one use of this type of wave. [2] c) (i) Name the radiations which are absorbed by greenhouse gases in the earth s atmosphere. (ii) A radiation X is focused by a particular device on the bulb of a thermometer and mercury in the thermometer shows a rapid increase. Name the radiation X. [2] d) (i) Name a prism required for obtaining a spectrum of Ultraviolet light. (ii) Name the radiations which can be detected by a thermopile. [2] e) Why is the colour red used as a sign of danger? [2] This paper consists of four printed pages. Question 3 a) Specific heat capacity of a substance A is 3,800 Jkg-1K-1 and that of a substance B is 400 Jkg-1K -1 . Which of the two substances is a good conductor of heat? Give a reason for your answer. [2] b) (i) Name the device used to protect the electric circuits from overloading and short circuits. (ii) On what effect of electricity does the above device work? c) Define the term 'Heat capacity' and state its S.I. unit. [2] d) (i) How can a temperature in degree Celsius be converted into S.I. unit of temperature? (ii) A liquid X has the maximum specific heat capacity and is used as a coolant in Car radiators. Name the liquid X. [2] e) A solid metal weighing 150 g melts at its melting point of 800 C by providing heat at the rate of 100 W. The time taken for it to completely melt at the same temperature is 4 min. What is the specific latent heat of fusion of the metal? [2] Question 4 a) Which of the radioactive radiations: [2] (i) can cause severe genetic diseases? (ii) are deflected by an electric field? b) (i) What do you understand by the term nuclear fusion? (ii) Nuclear power plants use nuclear fission reaction to produce electricity. What is the advantage of producing electricity by fusion reaction? [2] c) (i) What are isobars? (ii) Give one example of isobars. [2] d) Identify the following wires used in a household circuit: [2] (i) The wire is also called as the phase wire. (ii) The wire is connected to the top terminal of a three pin socket. e) Calculate the effective resistance across AB: [2] SECTION B Attempt any four questions from this section Question 5 a) A stone of mass m is rotated in a circular path with a uniform speed by tying a strong string with the help of your hand. Answer the following questions: [3] (i) Is the stone moving with a uniform or variable speed? (ii) Is the stone moving with a uniform acceleration? In which direction does acceleration act? b) (i) A body is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy as its velocity becomes zero? (ii) Draw a diagram to show how a single pulley can be used so as to have its ideal M.A= 2. [3] c) From the diagram given below. Answer the questions that follow: [3] (i) What kind of pulleys are A and B? (ii) State the purpose of pulley B. 2 (iii) What effort has to be applied at C just raise the load L=20 kgf? (Neglect the weight of pulley A and friction) Question 6 a) (i) A fuse is rated 8A. Can it be used with an electrical appliance rated 5 KW, 200 V? Give a reason. (ii) Name two safety devices which are connected to the live wire of a household electric circuit.[3] b) (i) Write one advantage of connecting electrical appliance in parallel combination. (ii) What characteristic should a fuse wire have? (iii) Which wire in a power circuit is connected to the metallic body of the appliance? [3] c) A cell of Emf 2 V and internal resistance 1.2 is connected with an ammeter of resistance 0.8 and two resistors of 4.5 and 9 as shown in the diagram below: [4] (i) What would be the reading on the Ammeter? (ii) What is the potential difference across the terminals of the cell? Question 7 a)A lens produces a virtual image between the object and the lens. [3] (i) Name the lens. (ii) Draw a ray diagram to show the formation of this image. d) (i) Why does the Sun appear red at sunrise? (ii) Name the subjective property of light related to its wavelength. [3] (c) What do you understand by the term Scattering of light ? Which colour of white light is scattered the least and why? [4] Question 8 a) A person standing between two vertical cliffs and 480 m from the nearest cliff shouts. He hears the first echo after 3s and the second echo 2s later. Calculate: [3] (i) The speed of sound. (ii) The distance of the other cliff from the person. b) In the diagram below, A, B, C, D are four pendulums suspended from the same elastic string PQ. The length of A and C are equal to each other while the length of pendulum B is smaller than that of D. Pendulum A is set in to a mode of vibrations. [3] (i) Name the type of vibrations taking place in pendulums B and D? (ii) What is the state of pendulum C? (iii) State the reason for the type of vibrations in pendulum B and C. c) (i) Name the phenomenon involved in tunning a radio set to a particular station. (ii) Define the phenomenon named by you in part (i) above. (iii) What do you understand by loudness of sound? (iv) In which units is the loudness of sound measured? 3 [4] Question 9 a) How much heat energy is released when 5 g of water at 20OC changes to ice at 0OC. [Specific heat capacity of water = 4.2 J g-1 OC-1 Specific latent heat of fusion of ice = 336 J g-1] [3] b) (i) Define Calorimetry. (ii) Name the material used for making a Calorimeter. (iii) Why is a Calorimeter made up of thin sheets of the above material answered in (ii)? [3] c) The melting point of naphthalene is 80 C and the room temperature is 30 C. A sample of liquid naphthalene at 100 C is cooled down to the room temperature. Draw a temperature time graph to represent this cooling. In the graph, mark the region which corresponds to the freezing process. [4] Question 10 a) A radioactive nucleus undergoes a series of decays according to the sequence. If mass number and atomic number of X3 are 172 and 69 respectively, what is mass number and atomic number of X?[3] b) The ore of Uranium found in nature contains 92U238 and 92U235. Although both the isotopes are fissionable, it is found out experimentally that one of the two isotopes is more easily fissionable. [3] (i) Name the isotope of Uranium which is easily fissionable. (ii) Give a reason for your answer. (iii) 'Write a nuclear reaction when Uranium 238 emits an alpha particle to form a Thorium (Th) nucleus. c) (i) Define nuclear fission. (ii) Rewrite and complete the following nuclear reaction by filling in the atomic number of Ba and mass number of Kr: [4] 4
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