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Pre Council Examination - 2019 Class XII Paper- I Physics (Theory) Time:-3hrs AL-70 M.M.70 Candidate are allowed additional 15 minutesfor only reading the paper They must not start writing during the time. SECTION - A Question 1. (A) Choose the correct al~ernative (a), (b), (c) or (d) for each of the questions given below : (i) The air between the plates of a capacitor is replaced by a medium of permittivity K. The potential difference between the plates : (a) increases K times (b) decreases K times (c) increas~s .JK times (d) decreases .JK times (ii) The time-constant of a circuit having a capacitor C and a resistor R in series is : (a) (c) (iii) CR (b) C R (d) ./CR R C A ligh~ raf passes from vacuum into a medium of refractive index n. The angle of refraction IS found to be half of the angle of incidence. The angle of incidence is : (a) cos- 1 (b) (~) 2cos-1 ( ~ ) 2 (c) ,_M__ 2 - ~ ' ~}~J._, ----- 2 2sin-1 (n) (d) Jt 2Y1-J {J " 1~ l ~ (iv) Dimensions of Planck's constant are same as of : . (a) force x time (c) energy/time (v) As a result of radioactive decay, emitted during lhis decay are : 92 U 238 (b) energy x distance (d) energy x time nucleus is converted into rj~ 91 c/ ~ fx Pa 234 Th particles (a) a proton and a neutron (b) an a-particle and a J3-particle (c) two fl-particles and a neutron (d) two f3-particles and a proton (B) Answer the following questions briefly and to the point : (i) \ (ii) In an a.c: circ1:it, the voltage of supply is 300 V. What is rms voltage ? How does an induct<;>r behave in a d.c. circuit? field B and velocity_ vector c are mutually perpendicular to each other, for a linearly polarized ray of light. Identify (name) three different planes, which are mutually perpendicular to each other. (iv) When thin transparent film is placed just infront of one of the slits in the Young's double slit experiment using white light, what change results in frin ge system? (v) Give two differences between diffraction fringes formed by a single slit and interference fringes formed by Young's double slit. (vi) A lens whose radii of curvature are different is forming the image of an object placed on its~s. If the lens is reversed, will the position of the imagE> change? (vii) What will be the nature of graph between de-Broglie wavelength and momentum of a moving particle ? (iii) At any instant, the electric field E, magnetic a (1) +2 Paper - I Physics (Theory) (1-4)
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