Buds Public School, Dubai NAME: PHYSICS GRADE-12 Topic – Moving Charges and Magnetism __worksheet_-1_____________________________________________________ 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? 2. An electron in an atom revolves round the nucleus in an orbit of radius r with frequency v. Write the expression for the magnetic moment of the electron. 3. Write the expression for the magnetic force acting on a charged particle moving with velocity in the presence of magnetic field B. 4. An electron does not suffer any deflection while passing through a region of uniform magnetic field. What is the direction of the magnetic field? 5. Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why? 6. Show the variation of resistivity with temperature for a typical semiconductor 7. 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. 8. 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 9. .State 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 turn and carrying a steady current ‘I’. Draw the magnetic field lines of a finite solenoid carrying current I. 9. State Ampere’s circuital law. Use this law to find magnetic field due to straight infinite current carrying wire. How are the magnetic field lines different from electrostatic field lines? OR A long straight wire of a circular cross-section of radius ‘a’ carries a steady current ‘I’. The current is uniformly distributed across the cross-section. Apply Ampere’s circuital law to calculate the magnetic field at a point ‘r’ in the region for (i) r < a and (ii) r > a. 3 10. State Ampere’s circuital law. Use this law to obtain the expression for the magnetic field inside an air cored toroid of average radius ‘r’, having ‘n’ turns per unit length and carrying a steady current I. 11. A neutron, an electron and an alpha particle moving with equal velocities, enter a uniform magnetic field going into the plane of the paper as shown. Trace their paths in the field and justify your answer. 12a) A point charge q moving with speed v enters a uniform magnetic field B that is acting into the plane of the paper as shown. What is the path followed by the charge q and in which plane does it move? (b) How does the path followed by the charge get affected if its velocity has a component parallel to B (c) If an electric field E is also applied such that the particle continues moving along the original straight line path, what should be the magnitude and direction of the electric field E OR Describe the path of a charged particle moving in a uniform magnetic field with initial velocity (i) Parallel to the field (ii) Perpendicular to the field (iii) At an arbitrary angle Ѳ (0˂ Ѳ˃ 90̊) 13. Two long straight parallel conductors carry steady current I1 and I2 separated by a distance d. If the currents are flowing in the same direction, show how the magnetic field set up in one produces an attractive force on the other. Obtain the expression for this force. Hence define one ampere (b) Show with the help of a diagram how the force between the two conductors would change when the currents in them flow in the opposite directions. 14. Deduce the expression for the torque acting on a planar loop of area A and carrying current I placed in a uniform magnetic field B. If the loop is free to rotate, what would be its orientation in stable equilibrium? OR Derive the expression for the torque on a rectangular current carrying loop suspended in a uniform magnetic field. 15. With the help of a labelled diagram, state the underlying principle of a cyclotron. Explain clearly how it works to accelerate the charged particles. Show that cyclotron frequency is independent of energy of the particle. Is there an upper limit on the energy acquired by the particle ? Give reason. 16. Deduce an expression for the cyclotron frequency and show that it does not depend on the speed and radius of the charged particle. What is resonance condition? How is it used to accelerate charged particle? 17. Draw a labelled diagram of a moving coil galvanometer. State the underlying principle of working of a moving coil galvanometer. Write two reasons why a galvanometer cannot be used as such to measure current in a given circuit. Name any two factors on which the current sensitivity of a galvanometer 18. (a) Why is the magnetic field radial in a moving coil galvanometer? Explain how it is achieved. (b) A galvanometer of resistance ‘G’ can be converted into a voltmeter of range (0-V) volts by connecting a resistance ‘R’ in series with it. How much resistance will be required to change its range from 0 to V/2 ? (C)Write two factors on which the current sensitivity of a moving coil galvanometer depend. 19. Deduce the expression for magnetic dipole moment of an electron revolving around the nucleus in a circular orbit of radius r. Indicate direction of dipole moment. 20. __________________________________
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