Title MOVING CHARGES AND MAGNETISM.docx.pdf ✅

4.MOVING CHARGES AND MAGNETISM Single Correct Answer Type 1. A particle moving in a magnetic field increases its velocity then its radius of the circle a) Decreases b) Increases c) Remains the same d) Becomes half 2. A wire carrying current I and other carrying 2I in the same direction produces a magnetic field B at the mid point. What will be the field when 2I wire is switched off a) B/2 b) 2B c) B d) 4B 3. Two long parallel copper wires carry currents of 5A each in opposite directions. If the wires are separated by a distance of 0. 5m, then the force between the two wires is a) 10 , attractive −5N b) 10 , repulsive −5N c) 2×10 , attractive −5N d) 2×10 , repulsive −5N 4. An infinitely long straight conductor AB is fixed and a current is passed through it. Another movable straight wire CD of finite length and carrying current is held perpendicular to it and released. Neglect weight of the wire a) The rod CD will move upwards parallel to itself b) The rod CD will move downward parallel to itself c) The rod CD will move upward and turn clockwise at the same time d) The rod CD will move upward and turn anti-clockwise at the same time 5. Two similar coils of radius R are lying concentrically with their planes at right angles to each other. The currents flowing in them are Iand 2I, respectively. The resultant magnetic field induction at the centre will be a) 5μ 0 I 2R b) 3μ 0 I 2R c) μ 0 I 2R d) μ 0 I R 6. A current (i) carrying circular wire of radius R is placed in a magnetic field B perpendicular to its plane. The tension T along the circumference of wire is a) BiR b) 2πBiR c) πBiR d) 2BiR 7. A current of i ampere flows in a circular area of wire which subtends an angle of (3π/2) radian at its centre, whose radius is R. The magnetic induction B at the centre is a) μ 0 i/R b) μ 0 i/2R c) 2μ 0 i/R d) 3μ 0 i/8R Page| 1
8. A wire in the form of a circular loop of one turn carrying a current produces a magnetic field B at the centre. If the same wire is looped into a coil of two turns and carries the same current, the new value of magnetic induction at the centre is a) 3B b) 5B c) 4B d) 2B 9. In which orientation the resultant magnetic moment of two magnets, will be zero, if magnetic moment of each magnets is M in the following figures? a) b) c) d) 10. A square frame of side 1 m carries a current i, produces a magnetic field B at its centre. The same current is passed through a circular coil having the same perimeter as the square. The magnetic field at the centre of the circular coil is B'. The ratio B/B’ is a) 8 π 2 b) 8 2 π 2 c) 16 π 2 d) 16 2π 2 11. Two charged particles are projected into a region in which a magnetic field is perpendicular to their velocities. After they enter the magnetic field, you can conclude that a) The charges are deflected in opposite directions b) The charges continue to move in a straight line c) The charges move in circular paths d) The charges move in circular paths but in opposite directions 12. Through two parallel wires A and B, 10A and 2A of currents are passed respectively in opposite directions. If the wire A is infinitely long and the length of the wire B is 2m, then force on the conductor B, which is situated at 10 cm distance from A, will be a) 8 ×10 N −7 b) 8 ×10 N −5 c) 4 ×10 N −7 d) 4 ×10 N −5 13. A circular loop carrying a current is replaced by an equivalent magnetic dipole. A point on the axis of the loop is a) An end-on position b) A broad side-on position c) Both (a) and (b) d) Neither (a) nor (b) 14. A horizontal rod of mass 10 gm and length 10 cm is placed on a smooth plane inclined at an angle of 60° with the horizontal, with the length of the rod parallel to the edge of the inclined plane. A uniform magnetic field of induction B is applied vertically downwards. If the current through the rod is 1. 73 ampere, then the value of B for which the rod remains stationary on the inclined plane is a) 1.73 tesla b) 1 1.73 tesla c) 1 tesla d) None of the above 15. An electron revolves in a circle of radius 0. 4 Å with a speed of 10 . The magnitude of the magnetic 5 ms −1 field, produced at the center of the circular path due to the motion of the electron, in weber metre is −2 a) 0.01 b) 10.0 c) 1.0 d) 0.005 16. A 100 turns coil shown in figure carries a current of 2 amp in a magnetic field B = 0. 2 Wb/m . The torque 2 acting on the coil is Page| 2
a) 0.32 Nm tending to rotated the side AD out of the page b) 0.32 Nm tending to rotated the side AD into the page c) 0.0032 Nm tending to rotated the side AD out of the page d) 0.0032 Nm tending to rotated the side AD into the page 17. Two concentric coils each of radius equal to 2πcm are placed at right angles to each other. 3 A and 4 A are the currents flowing in each coil respectively. The magnetic induction in Wbm at the centre of the coils −2 will be μ 0 = 4π × 10 −7WbAm −1 ( ) a) 12×10 −5 b) 10 −5 c) 5×10 −5 d) 7×10 −5 18. A thin circular wire carrying a current I has a magnetic moment M. The shape of the wire is changed to a square and it carries the same current. It will have a magnetic moment a) M b) 4 π 2 M c) 4 π M d) π 4 M 19. Two parallel long wires carry currents i and with . When the currents are in the same direction, 1 i 2 i 1 > i 2 the magnetic field midway between the wires is 10μT. When the direction of i is reversed, it becomes 2 40 μT. The ratio i is 1 /i 2 a) 3 : 4 b) 11 : 7 c) 7 : 11 d) 5 : 3 20. A straight wire of length π is carrying a current of and the magnetic field due to it is measured 2 ( ) metre 2A at a point distance 1 cm from it. If the wire is to be bent into a circle and is to carry the same current as before, the ratio of the magnetic field at its centre to that obtained in the first case would be a) 50 : 1 b) 1 : 50 c) 100 : 1 d) 1 : 100 21. A proton of energy 8 eV is moving in a circular path in a uniform magnetic field. The energy of an alpha particle moving in the same magnetic field and along the same path will be a) 4 eV b) 2 eV c) 8 eV d) 6 eV 22. An electron and proton having same kinetic energy enter into magnetic field perpendicular to it. Then a) The path of electron is less curved b) The path of proton is less curved c) Both have equal curved paths d) Both have straight line paths 23. A coil of n number of turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current of strength I is passed through the coil, the magnetic field at its centre is a) μ 0 nI (b−a) a b b) μ 0 nI 2(b−a) c) 2μ 0 nI b d) μ 0 nI 2(b−a) b a 24. A beam of protons is moving parallel to a beam of electrons. Both the beams will tend to a) Repel each other b) Come closer c) Move more apart d) Either (b) or (c) Page| 3
25. A fixed horizontal wire carries a current of 200 A. Another wire having a mass per unit length 10 is −2 kg/m placed below the first wire at a distance of 2 cm and parallel to it. How much current must be passed through the second wire if it floats in air without any support? What should be the direction of current in it a) 25 A (direction of current is same to first wire) b) 25 A (direction of current is opposite to first wire) c) 49 A (direction of current is same to first wire) d) 49 A (direction of current is opposite to first wire) 26. A long solenoid of length L has a mean diameter D. It has n layers of winding of N turns each. If it carries a current I, the magnetic field at its centre will be a) Proportional to D b) Inversely proportional to D c) Independent of D d) Proportional to L 27. Two galvanometer A and B require 3mA and 5mA respectively to produce the same deflection of 10 divisions. Then a) A is more sensitive than B b) B is more sensitive than A c) A and B are equally sensitive d) Sensitiveness of B is 5/3 times that of A 28. A circular current carrying coil has a radius R. The distance from the centre of the coil on the axis of the coil, where the magnetic induction is th of its value at the centre of the coil is 1 8 a) 3R b) R/ 3 c) 2 ( 3 )R d) R 2 3 29. The coil of a galvanometer consists of 100 turns and effective area of 1 square cm. The restoring couple is 10 . The magnetic field between the pole pieces is . The current sensitively of this −8N − m/radian 5 T galvanometer will be a) 5×10 −4 rad/μ amp b) 5×10 −6 per amp c) 2×10 −7 per amp d) 5 rad/μ amp 30. A charged particle of mass m and charge q travels in a circular path of radius r that is perpendicular to a magnetic field B. The time taken by the particle to complete one revolution is a) 2πB m b) 2π m q B c) 2π mq B d) 2π q 2B m 31. Two circular coils are made of two identical wires of same length. If the number of turns of two coils are 4 and 2, then the ratio of magnetic induction at centres will be zero a) 4 : 1 b) 2 : 1 c) 1 : 2 d) 1 : 1 32. A long, straight wire is turned into a loop of radius 10 cm (see figure). If a current of 8 amperes is passed through the lop, then the value of the magnetic field and its direction as the centre C of the loop shall be close to a) 5. 0×10 Newton/(amp-meter), upward −5 Page| 4