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PRACTICE PAPER 1 (2020-21) Physics (2hours) 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 four 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) A pulley system has five pulleys in all and is 90% efficient. Calculate: [2] (i) the mechanical advantage (ii) the effort required to lift a load of 1000N. b) Is any work done by a force, used to carry hand bag, if the person is [2] walking on: (1) level road? (2) climbing stairs? c) State the law of conservation of energy. [2] d) A ball of mass 200 g falls from a height of 5 m. What will be its kinetic [2] energy when it just reaches the ground? (g = 9.8 ms-2) e) A spring is kept compressed by a small trolley of mass 400 g lying on a [2] smooth horizontal surface as shown in the figure. When the trolley is released, it is found to move at a speed v = 3 ms-1. What potential energy did the spring possess when compressed? Question 2 a) Give one example each when: [2] (i) Chemical energy changes into electrical energy. (ii) Electrical energy changes into chemical energy. b) Sometime the air bubbles emerging out of a fish tank appear silvery. [2] Why? c) Draw a diagram to show dispersion of white light by an equilateral [2] prism. d) State the conditions required for total internal reflection of light to take [2] place. e) A sound made on the surface of a lake takes 3 s to reach a boatman. [2] How much time it will take to reach a diver inside the water at the same depth? [velocity of sound in air = 330 ms-1; velocity of sound in water = 1450 ms-1] Question 3 a) Give two characteristic properties of copper wire which make it [2] unsuitable for use as fuse wire. b) Name the material which is used as a fuse wire. [2] c) Name the SI unit of: [2] (i) Moment of force. (ii) Rate of change of momentum. d) 8 bulbs of resistance 200 each are connected to 200 V supply in a [2] parallel circuit. Calculate : (i) The combined resistance of 8 bulbs. (2) Current flowing through each bulb. e) Two bulbs are marked 100 W-220 V and 200 W-220 V respectively. [2] Calculate the ratio of their resistances. Question 4 a) i. A monochromatic beam of light of wavelength passes from air [2] into a glass block. Write an expression to show the relation betwen the speed of light in air and the speed of light in glass. ii.As the ray of light passes from air to glass, state how the wavelength of light changes. Does it increase, decrease or remain constant? b) A wire of uniform thickness with a resistance of 64 is cut into four [2] equal pieces and they are joined in parallel. Find the resistance of the parallel combination. c) An electric bulb gives much brighter light when the magnitude of emf [2] increases. Explain. d) An electric kettle is rated 220 V, 100 V. [2] i) What is the resistance of its element when in use? ii) What is the safe value of current that can pass through its element? e) In what way will the temperature of water at the bottom of a waterfall be [2] different from the temperature at the top? Give a reason for your answer. Section B (40 marks) (Attempt any four questions from this section) Question 5 a) (i) Where does the position of centre of gravity lie for 1. a circular lamina [3] 2. A triangular lamina? (ii) From the ground floor, a man comes up to fourth floor of a building using a staircase. Another person comes up to the same floor, using an elevator. Neglecting friction, compare the work done in two cases. b) (i) What do you understand by the term power? [3] (ii) The power of an electric motor is 5 kW. At what speed it can raise a load of 25000 N? c) State the law of conservation of energy. Support your answer by a [4] simple experiment. Question 6 a) Three resistors of 6. , 2. and 4.0 respectively are joined together [4] as shown in the figure. The resistors are connected to an ammeter and to a cell of e.m.f 6 V. Calculate: i. The effective resistance of the circuit. ii. The current drawn from the cell. b) State the characteristics of image formed when an object is placed (i) [3] between F and 2F, (ii) F and O of a convex lens.iii) at infinity c) Answer the following questions regarding the spectrum of ultraviolet rays: (i) On which side of visible spectrum, it is formed. (ii) What is the range of ultraviolet spectrum? (iii) Name the material of prism which absorbs least amount of ultraviolet ray. [3] Question 7 a) What are the factors on which the focal length of a lens depends? b) (i) State the Ohm law. (ii) What is the principle on which sonar is based? c) i. Sometimes when a vehicle is driven at a particular speed, a [3] [2] [1] [4] rattling sound is heard. Explain briefly; why this happens and give the name of the phenomenon taking place. ii. Suggest one way by which the rattling sound could be stopped. Question 8 a) (i) What do you understand by the term refraction of light? [3] (ii) The refractive index of diamond with respect to air (a d) = 2.4. Express the refractive index of air with respect to diamond. b) Why do the diamonds sparkle? [2] c) (i) Define the following for a convex lens. [5] (1) optical centre (2) principal focus (3) principal axis. (ii) Velocity of light in air is 3 x 108 ms-1 and in liquid P is 1.8 x 108 ms-1. Calculate the refractive index of the material P. Question 9 a) Study the diagram alongside carefully and calculate the magnitude of the current shown by the ammeter when: (i) Switch K is open. (ii) Switch K is closed. (iii) Give a reason for difference in reading in (i) and (ii). [4] b) ii) How does the heat produced in a wire or a conductor depend upon [4] the: (1) current passing through the conductor. (2) resistance of the conductor? ii) A ray of light travelling in air enters obliquely into water. Does the light ray bend towards or away from the normal? Explain. c) A convex lens forms a real and inverted image of a needle at a distance [2] of 50 cm from it. Where is the needle placed in front of the convex lens if the size of the object? Also find the power of the lens. Question10 a) i) Sketch a graph to show the change in potential difference across the ends [2] of an ohmic resistor and the current flowing in it. Label the axes of four graph. ii) What does the slope of the graph represent? b) State two differences between natural vibrations and damped vibration. [2] c) State two conditions for an echo to be heard distinctly. [2] d) An electrical heater is rated 4 kW, 220 V. Find the cost of using this heater [2] for 12 hours if one kWh of electrical energy costs Rs. 3.25. e) A man standing between two vertical cliffs and 680 m away from the [2] nearest cliff, produces sound. He hears the first echo after 4 s and second echo 5 s later. Calculate : (i) the speed of sound in air and (ii) the distance between the cliffs. ***************************
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