Class – XII
Time-3 hr.Date- 10/02/11Marks-70
i) All questions are compulsory.
ii) There are 30 questions in total. Questions 1 to 8 carry one mark each, questions 9 to 18 carry two marks each, questions 19 to 27 carry three marks each and questions 28 to 30 carry five marks each. iii) There is no overall choice. However ,an internal choice has been provided in one question of two marks, one question of three marks and all three questions of five marks each. You have to attempt only one of the choices in such questions. iv) Use of calculators is not permitted.
v) You may use the following values of physical constants wherever necessary :
c = 3 x 108 ms-1
h = 6.626 x 10-34 Js
e = 1.602 x 10-19 C
µ0= 4π x 10-7 TmA-1
1 = 9 x 109 Nm2C-2
Mass of electron me= 9.1 x 10-31 kg
Mass of neutron mn= 1.675 x 10-27 kg
Boltzmann’s constant k =1.381 x 10-23 JK-1
Avogadro’s number NA = 6.022 x 1023 mol-1
Radius of earth = 6400 km
UNITS- 1. ELECTROSTATICS 2.CURRENT ELECTRICITY 3.MAGNETIC EFFECT OF CURRENT AND MAGNETISM 4. EMI & AC 5. EM Waves.
Q.1 How is the relative permeability (µr) of a material related to its susceptibility (χm) ?1 Q.2 A metallic wire 1 m in length is moving normally across a field of 0.1 T with a speed of 5 ms-1. Find the emf between the ends of the wire.1 Q.3 What is the angle between the directions of electric field at any (i) axial point and (ii) equatorial point due to an electric dipole ?1 Q.4 A(hypothetical) bar magnet (AB) is cut into two equal parts. One part is now kept over the other, so that pole C2 is above C1. If M is the magnetic moment of the original magnet, what would be the magnetic moment of the combination so formed ?1
Q.5 The graph shown here, shows the variation of the total energy (E) stored in a capacitor against the value of the capacitance (C) itself .Which of the two-the charge on the capacitor or the potential used to charge it is kept constant for this graph ? 1
Q.6 An α-particle and a proton are moving in the plane of the paper in a region where there is a uniform magnetic field (B) directed normal to the plane of the paper. If the two particles have equal linear momenta, what will be the ratio of the radii of their trajectories in the field ?1 Q.7 An electrical element X, when connected to an alternating voltage source, has the current through it leading the voltage by π/2 radians . Identify X and write an expression for its reactance.1 Q.8 Two plane sheets of charge densities +σ and – σ are kept in air as shown in Fig. what are the electric field intensities at points A and B ?1
Q.9 What is the magnitude of magnetic force per unit length on a wire carrying a current of 8 A and making an angle of 300 with the direction of a uniform magnetic field of 0.15 T ?2 Q.10 State Lenz’s law. Predict the polarity of the capacitor in the situation described by fig.
Q.11 (i) Draw the graphs showing variation of inductive reactance and capacitive reactance with frequency of applied a.c. source. (ii) Can the voltage drop across the inductor or the capacitor in a series LCR-circuit be greater than the applied voltage of the a.c. source ? Justify your answer.2 Q.12 Calculate the temperature at which the resistance of a conductor becomes 20% more than its resistance at 270C .The value of the temperature coefficient of resistance of the conductor is 2.0 x 10-4 /K.2
.13 Two cells of emf E1 and E2 have internal resistance r1 and r2. Deduce an expression for...