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CONTINUOUS ASSESSMENT - II Academic Year Class Maximum Marks Duration Month Subject : : : : : : 2020 2021 12 25 1 hour October Physics Subject Teacher e-mail: binoy.shomeonlineexam@gmail.com PHYSICS (Candidates are allowed to write between 8:00 Am -8:50 am Last 10 minutes are to upload the answer script / answers on the mail Id) Answer all questions in Section -A and Section - B The intended marks for questions or part of questions are given in brackets [ ]. Additional instructions as the per the subject requirement. Section-A Answer all questions. Question 1 (A) Choose the correct alternative (a), (b), (c) or (d) for each of the questions given below: (i) (ii) [ 2 1] The magnetic dipole moment of a current carrying coil does not depend upon (a) number of turns of the coil. (b) cross-sectional area of the coil. (c) current flowing in the coil. (d) material of the turns of the coil. When a charged particle is projected perpendicular to a uniform magnetic field, it describes a circular path in which. (B) (a) its speed remains constant. (b) its velocity remains constant. (c) its momentum remains constant. (d) its kinetic energy increases. Answer the following questions briefly and to the point. (i) [3 1] A particle of mass m and charge q moving with velocity v enters the region of uniform magnetic field at right angle to the direction of its motion. How does its kinetic energy get affected? This paper consists of 4 printed pages. Turn Over (ii) 1. State Lenz' s Law. 2. Figure shows a current carrying solenoid moving towards a conducting loop. Find the direction of the current induced in the loop. (iii) Write an expression of magnetic flux density 'B' at a point in end - on position or an axial position of a magnetic dipole. (Derivation not required.) Section B Answer all questions Question 2 [2] An ammeter of resistance 0.80 can measure current up to 1.0 A. (a) (i) What must be the value of shunt resistance to enable the ammeter to measure current up to 5.0 A? (ii) What is the combined resistance of the ammeter and the shunt? OR (b) Figure alongside shows a point P near a long conductor XY carrying a current I. MN is a short current carrying conductor, kept at the point P, parallel to the conductor XY. (i) What is the direction of magnetic flux density 'B' at the point P due to the current flowing through XY? (ii) What is the direction of the force experienced by the conductor MN due to the current flowing through XY? Question 3 What is motional emf? State any two factors on which it depends. Page 2 of 4 [2] Question 4 (a) [3] A square loop of side 20 cm carrying current of 1A is kept near an infinite long straight wire carrying a current of 2A in the same plane as shown in the figure. Calculate the magnitude and direction of the net force exerted on the loop due to the current carrying conductor. OR (b) A square shaped plane coil of area 100 cm2 of 200 turns carries a steady current of 5A. It is placed in a uniform magnetic field of 0.2 T acting perpendicular to the plane of the coil. Calculate the torque on the coil when its plane makes an angle of 60 with the direction of the field. In which orientation will the coil be in stable equilibrium? Question 5 (i) [3] Derive the expression for the magnetic energy stored in a solenoid in terms of magnetic field B and area A of the coil. (ii) A solenoid of area A and length l carrying a steady current I. How does this magnetic energy per unit volume compare with the electrostatic energy density stored in a parallel plate capacitor? Question 6 (a) [5] (i) Derive the expression for the torque on a rectangular current carrying loop suspended in a uniform magnetic field. (ii) A proton and a deuteron having equal momenta enter in a region of uniform magnetic field at right angle to the direction of the field. Depict their trajectories in the field. OR (b) (i) Define mutual inductance of a pair of coils and write on which factors does it depend. Page 3 of 4 (ii) A square loop of side 20 cm is initially kept 30 cm away from a region of uniform magnetic field of 0.1 T as shown in the figure. It is then moved towards the right with a velocity of 10 cm s-1 till it goes out of the field. Plot a graph showing the variation of Question 7 (a) 1. magnetic flux ( ) through the loop with time (t). 2. induced emf ( ) in the loop with time t. 3. induced current in the loop if it has resistance of 0.1 . [5] (i) Show how Biot-Savart law can be alternatively expressed in the form of Ampere s circuital law. Use this law to obtain the expression for the magnetic field inside a solenoid of length l , cross-sectional area A having N closely wound turns and carrying a steady current I . Draw the magnetic field lines of a finite solenoid carrying current I. (ii) A straight horizontal conducting rod of length 0.45 m and mass 60 g is suspended by two vertical wires at its ends. A current of 5.0 A is set up in the rod through the wires. Find the magnitude and direction of the magnetic field which should be set up in order that the tension in the wire is zero. (b) (i) OR Use Biot-Savart law to derive the expression for the magnetic field due to a circular coil of radius R having N turns at a point on the axis at a distance x from its centre. Draw the magnetic field lines due to this coil. (ii) A current I enters a uniform circular loop of radius R at point M and flows out at N as shown in the figure. Obtain the net magnetic field at the centre of the loop. Page 4 of 4
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