magnetism

1. A cell is connected between two points of a uniformly thick circular conductor. The magneeti field at the centre of the loop will be (a) Zero (b) (i1-i2) (c) (i1+ i2) (d) (i1-i2) 2. Two concentric coplanar circular loops of radii r1 and r2 carry currents of respectively i1 and i2 in opposite directions (one clockwise and the other anticlockwise.) The magnetic inducctio at the centre of the loops is half that due to i1 alone at the centre. If r2 = 2r1. the value of i2 /i1 is (a) 2 (b) 1/2 (c) 1/4 (d) 1 3. PQRS is a square loop made of uniform conducctin wire the current enters the loop at P and leaves at S. Then the magnetic field will be (a) Maximum at the centre of the loop (b) Zero at the centre of loop (c) Zero at all points inside the loop (d) Zero at all points outside of the loop 4. Two similar coils are kept mutually perpendiccula such that their centres coincide. At the centre, find the ratio of the magnetic field due to one coil and the resultant magnetic field by both coils. If the same current is flown (a) 1 : 2 (b) 1 : 2 (c) 2 : 1 (d) 3 : 1 5 In the figure, what is the magnetic field at the point O (a) (b) (c) (d) 6. Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half way between the wires is (a) (b) (c) (d) (e) 7. A proton moving with a constant velocity passes through a region of space without any change in its velocity. If and repressen the electric and magnetic fields respectivvely then this region of spece may have (a) E = 0, B = 0 (b) E = 0, B  0 (c) E  0, B = 0 (d) E  0, B  0 8. A uniform electric field and a uniform magneeti field are produced, pointed in the same direction. An electron is projected with its velocity pointing in the same direction (a) The electron will turn to its right (b) The electron will turn to its left (c) The electron velocity will increase in magnitude (d) The electron velocity will decrease in magnitude 9. Two particles X and Y having equal charges, after being accelerated through the same potenntia difference, enter a region of uniform magnetic field and describes circular path of radius R1 and R2 respectively. The ratio of max of X to that of Y is(a) (b) (c) (d) 10. The radius of curvature of the path of the charged particle in a uniform magnetic field is directly proportional to (a) The charge on the particle (b) The momentum of the particle (c) The energy of the particle (d) The intensity of the field 11. An electron is moving with a speed of 108 m/sec perpendicular to a uniform magnetic field of intensity B, Suddenly intensity of the magneeti field is reduced to B/2. The radius of the path becomes from the original value of r (a) No change (b) Reduces to r/2 (c) Increases to 2r (d) Stops moving 12. If a proton is projected in a direction perpendiicula to a uniform magnetic field with velocity v and an electron is projected along the lines of force, what will happen to proton and electron (a) The electron will travel along a circle with constant speed and the proton will move along a straight line. (b) Proton will move in a circle with constant speed and there will be no effect on the motion of electron (c) There will not be any effect on the motion of electron and proton (d) The electron and proton both will follow the path of a parabola 13. If a proton, deutron and a -particle on being accelerated by the same potential difference enters perpendicular to the magnetic field, then the ratio of their kinetic energies is (a) 1:2:2 (b) 2:2:1 (c) 1:2:1 (d) 1:1:2 14. A proton and a deutron both having the same kinetic energy, enter perpendicularily into a uniform magnetic field B. For motion of protto and deutron on circular path of radius Rp and Rd respectively, the correct statement is (a) Rd = 2 Rp (b) Rd = Rp 2 (c) Rd = Rp (b) Rd = 2 Rp 15. A proton (or charged particle) moving with velocity v is acted upon by eledctric field E and magnetic field B. The proton will move undeflected if (a) E is perpendicular to B (b) E is parallel to v and perpendicular to B (c) E, B and v are mutually perpendicular and v = (d) E and B both are parallel to v 16. A proton and electron both moving with the same velocity v enter into a region of magneeti field directed perpendicular to the veloccit of the particles. They will now move in circular orbits such that (a) Their time periods will be same (b) The time period for proton will be higher (c) The time period for electron will be higher (d) Their orbital radii will be same 17. A charge + Q is moving upwards vertically. It enters a magnetic field directed to the north. The force on the charge will be towaard (a) North (b) South (c) East (d) West 18. A charged particle of mass m and charge q describes circular motion of radius r in a uniform magnetic field of strength B. The frequency of revolution is (a) (b) (c) (d) 19. A particle of charge q and mass m moving with a velocity along the x-axis enters the region x > 0 with uniform magnetic field B along the direction. The particle will penetrate in this region in the x-direction upto a distance equal to (a) Zero (b) (c) (d) Infinity 20. A charged particle is moving in a uniform magnetic field in a circular path. Radiusof circular path is R. When energy of partiicl is doubled, then new radius will be (a) R2 (b) R3 (c) 2R (d) 3R 20. A charge q is moving in a magnetic field then the magnetic force does not depend upon (a) Charge (b) Mass (c) Velocity (d) Magnetic field 21. Two particles A and B of masses mA and mB respectively and having the same charge are moving in a plane. A uniform magnetic field exist perpendicular to this plane. The speeds of the particles are vA and vB respectively, and the trajectories are as shown in the figure. Then (a) mAvA< mBvB (b) mAvA> mBvB (c) mA