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ISC Class XI Prelims 2024 : Physics (Delhi Public School (DPS), Newtown, Kolkata)

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Snigdha Patra
Delhi Public School (DPS), Newtown, Kolkata

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DELHI PUBLIC SCHOOL NEWTOWN SESSION 2024-2025 FINAL EXAMINATION CLASS XI SUBJECT: PHYSICS [SET A] FULL MARKS: 70 TIME: 3 HOURS Instructions to Candidates You are allowed an additional 15 minutes for only reading the question paper. You must NOT start writing during reading time. This question paper has 5 printed pages and 20 questions. There are four sections in the paper: A, B, C and D. Internal choices have been provided in two questions each in Sections B, C and D. Section A consists of one question having fourteen sub-parts of one mark each. Section B consists of seven questions of two marks each. Section C consists of nine questions of three marks each. Section D consists of three questions of five marks each. The intended marks for questions are given in brackets [ ]. A simple scientific calculator without a programmable memory may be used for calculations. SECTION A [14 marks] Question 1 [1 7] A. Choose the correct answers to the questions from the given options. (i) The magnitude of the cross product of two vectors is equal to their dot product. The angle between the vectors is (a) /4 (b) /2 (c) (d) 0 (ii) The coefficient of restitution for perfectly elastic collision is (c) 1 (a) 0 (b) <1 (iii) The separation between two successive nodes or successive antinodes is (a) (b) (c) 2 (d) >1 (d) (iv) In a wire of Young s modulus Y the strain produced is X. The value of potential energy stored per unit volume will be (a) YX2 (b) 2YX2 (c) Y2X (d) YX2 (v) Assertion: Angular velocity of planets increases when they are nearest to the sun. Reason: Angular momentum of a planet is proportional to angular velocity. (a) Both Assertion and Reason are true and Reason is the correct explanation of the Assertion (b) Both Assertion and Reason are true but Reason does not correctly explain the Assertion (c) Assertion is true but Reason is false (d) Both the Assertion and Reason are false A/1 (vi) Pressure of an ideal gas is increased by keeping temperature constant. The kinetic energy of molecules (a) increases (b) decreases (c) remains the same (d) increases or decreases depending on the nature of the gas (vii) Assertion: The graph between velocity and displacement is parabolic in SHM. Reason: The velocity changes uniformly with displacement in SHM. (a) Both Assertion and Reason are true and Reason is the correct explanation of the Assertion (b) Both Assertion and Reason are true but Reason does not correctly explain the Assertion (c) Assertion is true but Reason is false (d) Both the Assertion and Reason is false B. Answer the questions briefly and with reference to the context: [1 7] (i) Define the term steady state condition for thermal conductivity of a body. (ii) What is the effect of temperature on Young s modulus of a material? (iii) What does the term isolated system mean with respect to motion of centre of mass? (iv) At what temperature will the rms speed of oxygen be equal to the rms speed of nitrogen at 0 C? (v) Mention any one condition for linear SHM. (vi) How many degrees of freedom are associated with a triatomic nonlinear rigid molecule at moderate temperature? (vii) What is meant by the term streamline flow of a liquid? SECTION B [14 marks] Question 2 State any two points of difference between isothermal and adiabatic processes. OR Why is a reversible process not realized in practice for working of a heat engine? [2] Question 3 The sum of two unit vectors is also a unit vector. Find the angle between them. [2] Question 4 [2] A projectile has a range 50 m and reaches a maximum height of 10 m. What is the angle of projection OR The trajectory of a projectile in a vertical plane is y = 3x projection and the speed of projection. Take g as 10 ms-2. m. Find the angle of Question 5 [2] A spring of spring constant K is cut into two equal pieces. Determine the spring constant of each individual piece. Question 6 [2] The density of material of a wire is 7500 kgm-3 and speed of transverse wave in the wire is 200 ms-1. What is the stress produced in the wire? A/2 Question 7 [2] With reference to amplitude of vibration and transfer of energy, how do stationary and progressive waves differ from each other? Question 8 [2] The mass and diameter of a planet are twice that of earth. What will be the time period of a second s pendulum on this planet? SECTION C [27 marks] Question 9 [3] 2 The moment of inertia of a body about a given axis is 1.5 kgm . The body was initially at rest. What should be the duration to have an angular acceleration of 20rads-2 to produce rotational kinetic energy 1200J? Question 10 [3] (i) (a) State the principle of continuity applicable for the flow of liquids. (b) The cylindrical tube of a spray pump has an area of 8cm 2, one end of which has 40 holes each of diameter 1mm. Find the speed of ejection of liquid through the holes if inside the tube the flow is at the rate of 1.5 m per min. OR (ii) (a) Write a relation between surface tension and work done to increase the surface area of a given surface. (b) A mercury drop of radius 1 mm breaks into 27 equal size droplets. If the surface tension of mercury is 0.465 N/m, find the work done in the process. Question 11 [3] Derive an expression for the thermal conductivity of two conductors having same cross section and thickness but of different materials when they are kept in parallel. Question 12 [3] -2 (i) Find out the acceleration of the 20 kg mass if the acceleration of 10kg is 10ms . OR (ii) Determine the tension in the string connecting the two blocks. Take g as 10ms-2. Question 13 [3] A block of mass m is placed on a surface with a vertical cross-section given by y = where x and y are expressed in m. If = 0.5, find the maximum height above the ground at which the block can be placed without slipping. A/3 Question 14 [3] How do you prove Avogadro s law from expression of pressure as given by kinetic theory of gases? Question 15 [3] The displacement vs time graph for a particle executing SHM is shown below. Draw the corresponding velocity vs time and acceleration vs time graphs keeping the values along the axis same. Question 16 Derive an expression for work done during adiabatic expansion of a gas. Question 17 Two wires P and Q are equally thick and of same material but LP = 2LQ. (i) Which of the wires undergoes greater extension for a given load? (ii) Mention the wire that will have a greater strain under a given load? [3] [3] SECTION D [15 marks] Question 18 [5] (i) (a) Derive an expression for the speed of sound proposed by Laplace for an ideal gas. (b) A wire has its fundamental frequency increased by 6 Hz, if the tension is increased by 44% keeping the length constant. Find the change in fundamental frequency if the length is increased by 20%, keeping the tension of the wire constant. OR (ii) (a) With the help of a neat diagram find out the ratio of the frequencies of any three modes of vibrations in an open organ pipe. (b) The difference in frequencies between the second overtone of a closed pipe and the first overtone of an open pipe of same length is 150 Hz. Determine the values of the fundamental frequencies of both pipes. Question 19 [5] (i) (a) Draw the variation of maximum energy of emitted radiation versus wavelength at two different temperatures. (b) A body cools from 80 C to 50 C in 5 minutes. How long will it take to cool from 60 C to 30 C if surrounding temperature be 20 C? . OR (ii) (a) Show that the root mean square speed of the molecules of a gas is proportional to the square root of absolute temperature of the gas. (b) If the root-mean-square velocity of Helium atoms at NTP be 1300 ms-1, estimate the density of Helium at 0 C and the mass of the atom. Take P = 1.01 105 Nm-2. A/4 Question 20 [5] Carnot s theorem is applicable only for the cyclical devices like heat engines, which states that the efficiency of an irreversible heat engine is always less than efficiency of a reversible engine operating between the same two reservoirs. The efficiencies of all reversible heat engines operating between the same two reservoirs are the same. (i) Why a Carnot s heat engine cannot be conceptualized in practice? (ii) State any one statement of second law of thermodynamics. (iii) What is meant by the term coefficient of performance in case of a heat pump? (iv) A Carnot engine takes 100 calorie heat from the source at 400K and rejects 80 calorie to the sink. Find the temperature of the sink and efficiency of the engine. A/5 A/6 A/7

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