Sample Class 12 Physics Exam Paper (2019-20), Exams of Physics

Download Sample Class 12 Physics Exam Paper (2019-20) and more Exams Physics in PDF only on Docsity! 1 CLASS - XII PHYSICS (042) SAMPLE QUESTION PAPER (2019-20) Time allowed: 3 hours Max. Marks: 70 General Instructions: 1. All questions are compulsory. There are 37 questions in all. 2. This question paper has four sections: Section A, Section B, Section C and Section D. 3. Section A contains twenty questions of one mark each, Section B contains seven questions of two marks each, Section C contains seven questions of three marks each, and Section D contains three questions of five marks each. 4. There is no overall choice. However, internal choices have been provided in two questions of one mark each, two questions of two marks, one question of three marks and three questions of five marks weightage. You have to attempt only one of the choices in such questions. 5. You may use the following values of physical constants where ever necessary. 2 Section – A Directions (Q1-Q10) Select the most appropriate option from those given below each question 1. A charge q is placed at the point of intersection of body diagonals of a cube. The electric flux passing through any one of its face is (a) (b) (c) (d) 1 2. The electric potential of earth is taken to be zero because earth is a good (a) Insulator (b) conductor (c) semiconductor (d) dielectric 1 3. If the ammeter in the given circuit shown in the diagram reads 2A, the resistance R is (a) 1Ω (b) 2Ω (c) 3Ω (d) 4Ω 1 4. The heat produced by 100W heater in 2 minutes is equal to (a) 10.5kJ (b) 16.3kJ (c) 12.0kJ (d) 14.2kJ 1 5. Time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of (a) speed of the particle (b) mass of the particle (c) charge of the particle (d) magnetic field 1 6. The final image formed in an astronomical refracting telescope with respect to the object is (a) Real inverted (b) Real erect (c) Virtual erect (d) Virtual inverted 1 7. The shape of the interference fringes in Young’s double slit experiment when D (distance between slit and screen) is very large as compared to fringe width is nearly (a) straight line (b) parabolic (c) circular (d) hyperbolic 1 5 Section – C 28 State working principle of potentiometer. Explain how the balance point shifts when value of resistor R increases in the circuit of potentiometer, given below. 3 29 Using Biot-Savart’s law, derive an expression for magnetic field at any point on axial line of a current carrying circular loop. Hence, find magnitude of magnetic field intensity at the centre of circular coil. 3 30 Obtain the resonant frequency and Q – factor of a series LCR circuit with L = 3H, C = 27𝛍F, R = 7.4Ω. It is desired to improve the sharpness of resonance of circuit by reducing its full width at half maximum by a factor of 2. Suggest a suitable way. 3 31 State the conditions of total internal reflection. Refractive indices of the given prism material for Red, Blue and Green colors are respectively 1.39, 1.48 and 1.42 respectively. Trace the path of rays through the prism. 3 32 Define resolving power of an astronomical refracting telescope and write expression for it in normal adjustment.Assume that light of wave length 6000Å is coming from a star, what is the limit of resolution of a telescope whose objective has a diameter of 2.54m? OR Write the basic assumptions used in the derivation of lens – maker’s formula and hence derive this expression. 3 3 6 33 Show that can not spontaneously emit a proton. Given: = 238.05079u, = 237.05121u = 1.00783u 3 34 Suggest an idea to convert a full wave bridge rectifier to a half wave rectifier by changing the connecting wire/s. Draw the diagram and explain your answer. 3 Section – D 35 (a) Using Gauss’s law, derive expression for intensity of electric field at any point near the infinitely long straight uniformly charged wire. (b)The electric field components in the following figure are Ex = αx, Ey = 0, Ez= 0; in which α = 400 N/C m. Calculate (i) the electric flux through the cube, and (ii) the charge within the cube assume that a = 0.1m. OR a) Define electrostatic potential at a point. Write its SI unit. Three charges q1 , q2 and q3 are kept respectively at points A, B and C as shown in figures. Write the expression for electrostatic potential energy of the system. b) Depict the equipotential surfaces due to (i) an electric dipole (ii) two identical negative charges separated by a small distance. 5 5 36 In the following diagram, the arm PQ of the rectangular conductor is moved from x = 0; outwards. 5 7 The uniform magnetic field is perpendicular to the plane and extends from x = 0 to x = b and is zero for x >b. Only the arm PQ possesses substantial resistance ‘r’. consider the situation when the arm PQ is pulled outwards from x = 0 to x = 2b, and is then moved back to x = 0 with constant speed ‘ѵ’. Obtain expressions for the (i) electric flux, (ii) the induced emf,(iii)the force necessary to pull the arm and (iv) the power dissipated as Joule heat. Sketch the variation of these quantities with distance. OR Write working principle of cyclotron and with a suitable diagram explain its working. Give any two applications of cyclotron. 5 37 Derive mirror equation for a convex mirror. Using it, show that a convex mirror always produces a virtual image, independent of the location of object. OR (a) Draw a ray diagram for final image formed at distance of distinct vision (D) by a compound microscope and write expression for its magnifying power. (b) An angular magnification (magnifying power) of 30x is desired for a compound microscope using as objective of focal length 1.25cm and eye piece of focal length 5cm. How will you set up the compound microscope? 5 5