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VIBGYOR HIGH First Preliminary Examination 2020-2021 PHYSICS Grade: X Max. Marks : 80 Date : 24/11/2020 Time Allowed: 2 hour 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. Section I is compulsory. Attempt any four questions from Section II. The intended marks for the questions or parts of questions are given alongside in brackets [ ]. _________________________________________________________________________ SECTION I (40 Marks) Attempt all questions from this Section. Question 1 a) (i) Name the physical quantity which is measured in calories. [2] (ii) How is calories related to the S.I. unit of that quantity? b) Is it possible to have an accelerated motion with a constant speed? [2] Name such type of motion. c) A quartz prism and not a glass prism is required for obtaining the spectrum of the [2] ultraviolet light. Give reasons d) Define the term velocity ratio.State its S.I. unit. [2] e) A sound wave travelling in water has wavelength 0.4 m. [2] Is this wave audible in air? (The speed of sound in water = 1400 ms -1) 1 Question 2 a) (i)How does an ideal machine differ from a practical machine? [2] (ii)State the relationship between mechanical advantage,velocity ratio and efficiency. b) (i) Where will the centre of gravity lie for a very thin circular disc? [2] (ii) Will the position of the centre of gravity change if a piece of the disc breaks off? c) A force F acts on a body and displaces it by a distance S in a direction at an angle [2] with the direction of force. (i) Write the expression for the work done by the force. (ii) What should be the angle between the force and displacement so that the work done is maximum? d) Which characteristic of sound will change if there is a change in [2] (i) its amplitude (ii) its waveform ? e) (i) What are mechanical waves? [2] (ii) Name one property of waves that do not change when the wave passes from one medium to another. Question 3 a) (i)Define the term principal axis of a lens. [2] (ii) When does a ray of light falling on a lens pass through it undeviated ? b) State two factors which affect the critical angle for a given pair of medium. [2] c) Arrange , , and rays in ascending order with respect to their [2] (i) Ionising power. (ii) Biological effect. d) State the position of the object in front of a converging lens if : [2] (i) It produces a real and same size image of the object (ii)It is used as a magnifying lens. e) A crane A lifts a heavy load in 5 seconds, whereas another crane B does the samework in 2 seconds. Compare the power of crane A to that of crane B . 2 [2] Question 4 a) What are the two characteristic properties of a fuse wire ? [2] b) Draw two rays from the point O of the object to show the formation of image I. [2] c) State the difference between a convex and a concave lens in their [2] (i)appearance and (ii) action on the incident light. d) A certain nucleus X has a mass number 202 and atomic number 84 .The nucleus [2] X changes to 82 Y 198 after a loss of a particle. (i)Name the particle emitted. (ii) Represent this change in the form of equation. e) 50 g of metal piece at 27 C requires 2400 J of heat energy to attain a [2] temperature of 327 C. Calculate the specific heat capacity of the metal. SECTION II (40 Marks) Attempt any four questions from this Section Question 5 a) (i) With reference to the direction of action, how does a centripetal force differ [3] from a centrifugal force during uniform circular motion? (ii) Is centrifugal force the force of reaction of centripetal force? (iii) Compare the magnitude of centripetal and centrifugal force. b) The figure below shows a simple pendulum of mass 200 g. It is displaced from the [3] mean position A to the extreme position B. The potential energy at the position A is zero. At the position B the pendulum bob is raised by 5 m. 3 (i)What is the potential energy of the pendulum at the position B? (ii) What is the total mechanical energy at point C? (iii) What is the speed of the bob at the position A when released from B? (Take g =10 ms-2 and there is no loss of energy.) c) (i) What is the effect of increase in pressure on the boiling point of liquids? [4] (ii) Some amount of paraffin wax having melting point 550C is heated from room temperature 300C till it melts completely. Draw its heating curve corresponding to the information given above. Question 6 a) A pulley system with a velocity ratio of 5 is used to lift a load of 150kgf through a [3] vertical height of 20 m.The effort required is 50kgf in the downward direction.Calculate: (i)The distance moved by the effort. (ii)The work done by the effort. (iii)The mechanical advantage of the system b) (i) Heat supplied to a solid changes it into liquid. What is this change in [3] phase called? (ii) During the phase change does the average kinetic energy of the molecules of the substance increase?. (iii)What is the relationship between heat capacity and specific heat capacity of a substance? c) An object of height 2 cm is placed in front of a convex lens of focal length 20 cm at a distance of 15 cm from it. Find: (i) the position of the image , (ii) the magnification and the nature of the image. 4 [4] Question 7 a) The diagram below shows a monochromatic light ray EF passing through a [3] rectangular glass block PQRS and emerging out of it. (i) Name the distance AB. (ii) State whether distance AB increases, decreases or remains the same when outside medium is replaced from air to water. (iii)Give a reason for the answer of (ii). b) The diagram below shows the displacement-time graph for a vibrating body. [3] i)Name the type of vibrations produced by the vibrating body. ii) Why is the amplitude of the wave gradually decreasing ? iii)What will happen to the vibrations of the body after some time? c) (i)Define the term dispersion of light. [4] (ii) State three properties which are common to all types of electromagnetic radiation. 5 Question 8 a) The diagram below shows a light source P embedded in a rectangular [3] glass block ABCD of critical angle 42 . Complete the path of the ray PQ till it emerges out of the block. [Write necessary angles.] b) (i)What are superconductors? [3] (ii) Calculate the current drawn by an appliance rated 110 W, 220 V when connected across 220 V supply. (iii) Name a substance whose resistance decreases with the increase in temperature. c) The diagram below shows three resistors connected across a cell of e.m.f. 1.8 V [4] and internal resistance r. Calculate: (i) Current through 3 resistor. (ii) The internal resistance r. Question 9 a) (i) Why is it easier to use MCB than a fuse in an electric circuit ? [3] (ii) To which wire of a cable in a power circuit should the (1) metal case of a geyser , (2) the switch be connected? b) (i)Name and state the law which relates the potential difference and current in a conductor. (ii) Calculate the effective resistance across the points A and B in the following figure. 6 [3] c) An electrical appliance can give an electric shock to its user under certain [4] circumstances. Mention any four of these circumstances. Question 10 a) Give three points of difference between single movable pulley and single fixed [3] pulley. b) A uniform meter rod of weight 50 gf is to be balanced at a 40 cm mark, and a [3] weight of 100 gf is suspended at the 5 cm mark. Where should one suspend a weight of 80 gf to balance the meter rod? c) (i) Represent the change in the nucleus of a radioactive element when a particle is emitted. (ii)Complete the diagram as given below by drawing the deflection of radioactive radiations in an electric field. ***** 7 [4]
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