Tiêu đề MAGNETIC EFFECT OF CURRENT & MAGNETISM.pdf ✅

Magnetic Effect of Current and Magnetism  Digital www.allendigital.in [ 93 ] MAGNETIC FIELD & BIOT-SAVART LAW 1. A stationary magnet does not interact with :- (1) iron rod (2) moving charge (3) moving magnet (4) stationary charge 2. Figure shows a square shape loop, whose one arm BC produces magnetic field B at the centre of coil. The resultant magnetic field due to all the arms will be :- (1) 4B (2) B/2 (3) B (4) 2B 3. A wire is parallel to one arm of a square current carrying loop, which also carries current. Now at any point A within the coil the magnetic field will be :- (1) less than the magnetic field produced due to loop only. (2) more than the magnetic field produced due to loop only. (3) equal to the earlier. (4) zero 4. A current of 10 A is established in a long wire along positive z -direction. The magnetic field B at the point (1m, 0, 0) is :- (1) 1 T along the –y direction (2) 2T along the +y direction (3) 1T along the –xdirection (4) 2T along the +x direction 5. Radius of current carrying coil is 'R'. Then ratio of magnetic fields at the centre of the coil to the axial point, which is R 3 distance away from the centre of the coil :- (1) 1 : 1 (2) 1 : 2 (3) 1 : 4 (4) 8 : 1 6. A coil of one loop is made by a wire of length L and there after a coil of two loops is made by same wire. The ratio of magnetic field at the centre of coils respectively :- (1) 1 : 4 (2) 1 : 1 (3) 1 : 8 (4) 4 : 1 7. Magnetic field at point O will be :- (1) μ I0 2R  (2) μ I0 2R (3) 0 μ I 1 1 2R     −     (4) μ I0 1 1 2R     +    8. The vector form of Biot savart law for a current carrying element is :- (1) 0 2 id sin dB 4 r   =  (2) 0 2 id rˆ dB 4 r   =  (3) 0 3 id rˆ dB 4 r   =  (4) 0 2 id r dB 4 r   =  9. A and B are two concentric circular loop carrying current i1 and i2 as shown in figure. If ratio of their radii is 1:2 and ratio of the flux densities at the centre O due to A and B is 1:3 then the value of 1 2 i i will be :- (1) 1 2 (2) 1 3 (3) 1 4 (4) 1 6 10. For the given current distribution the magnetic field at point, 'P' is :- (1) 0 4   (2) 0   (3) 0 2    (4) 0 2   – + i O i C B i i A O R I B A O i1 i2 5m 2.5m 5A P 2.5A Exercise - I
NEET : Physics [ 94 ] www.allendigital.in  Digital 11. 1A current flows through an infinitely long straight wire. The magnetic field produced at a point 1m. away from it is :– (1) 2 × 10–3 T (2) 2 10 T (3) 2 × 10–7 T (4) 2 × 10–6 T 12. Two infinite long parallel wires carry equal currents in same direction. The magnetic field at mid point between the two wires is :– (1) Twice the magnetic field produced due to each of the wires (2) Half of the magnetic field produced due to each of the wires (3) Square of the magnetic field produced due to each of the wires (4) Zero 13. A closely wound flat circular coil of 25 turns of wire has diameter of 10 cm and carries a current of 4 ampere. Determine the magnetic flux density at the centre of the coil :- (1) 1.679 × 10–5 T (2) 2.028 × 10–4 T (3) 1.257 × 10–3 T (4) 1.512 × 10–6 T 14.  ampere current is flowing through a long straight wire. Due to this a field of 5 × 10–5 T produced, then distance of the point from the axis of the wire is :- (1) 1040 m (2) 1050 m (3) 1060 m (4) 1080 m 15. Radius of a current carrying coil is ‘R’. The ratio of magnetic field at a axial point which is R distance away from the centre of the coil to the magnetic field at the centre of the coil :- (1) 1/2 1 2       (2) 1 2 (3) 3/2 1 2       (4) 1 4 16. When the current flowing in a circular coil is doubled and the number of turns of the coil in it is halved, the magnetic field at its centre will become :- (1) Same (2) Four times (3) Half (4) Double 17. Which of the following statement is not true; magnetic field at the centre of current carrying loop :- (1) proportional to current (2) inversely proportional to radius (3) proportional to number of turns (4) none 18. A circular coil of radius R carries an electric current. The magnetic field due the coil at a point on the axis of the coil located at a distance r from the center of the coil, such that r >> R varies as :- (1) 1/r (2) 1/r3/2 (3) 1/r2 (4) 1/r3 19. Two concentric circular loops of radii 0.08m and 0.1m carries current such that magnetic field at the centre is zero. If the current in the outer loop is 8A clockwise, current in the inner loop is :- (1) 6.4 A anticlockwise (2) 6.4 A clockwise (3) 8A anticlockwise (4) 3.2 A clockwise 20. In the shown figure magnetic field at point A will be :- (1) 0 I 4   (2) 0 I 4R  (3) 0 I 4 R   (4) Zero 21. If radius of coil becomes two times and current becomes half then magnetic field at centre of the coil will be :- (1) Two times (2) Four times (3) Half (4) One fourth 22. 2A current is flowing in a circular loop of radius 1m. Magnitude of magnetic field at the centre of circular loop will be :- (1) 0 2  (2) 20 (3) 0 (4) 0 2   I A R
Magnetic Effect of Current and Magnetism  Digital www.allendigital.in [ 95 ] 23. A horizontal overhead powerline is at a height of 4m from the ground and carries a current of 100 A from east to west. The magnetic field directly below it on the ground is :- (1) 2.5 10–7 T, southward (2) 5 × 10–6 T, northward (3) 5 × 10–6 T, southward (4) 2.5 × 10–7 T, northward 24. The wire in the figure carries a current i and consists of a circular arc of radius R and central angle 2  rad, and two straight sections whose extensions intersect the centre C of the arc. The magnetic field B that the current produces at C is :- (1) 0 μ i B 8R = into the plane of the figure (2) 0 μ i B 8R = out of the plane of the figure (3) 0 μ i B 8 R =  into the plane of the figure (4) 0 μ i B 8 R =  out of the plane of the figure AMPERE'S LAW 25. For the hollow thin cylindrical current carrying pipe which statement is correct :- (1) magnetic field inside the pipe is not zero (2) magnetic field outside the pipe is zero (3) electric field outside the pipe is zero (4) electric field on the surface of pipe is zero 26. In a current carrying long solenoid the field produced does not depend on :- (1) number of turns per unit length (2) current in solenoid (3) radius of cross section of the solenoid (4) all of the above 27. If length and number of turns becomes half for a solenoid then value of magnetic field becomes:- (1) twice (2) same (3) half (4) one fourth 28. If number of turns and current become double for any solenoid, then value of magnetic field becomes:- (1) twice (2) same (3) half (4) four times 29. A current of 1/4 ampere is flowing through a toroid. It has 1000 number of turn per meter then value of magnetic field (in Wb/m2) along its axis is :- (1) 10–2 (2) 10–3 (3) 10–4 (4) 10–7 30. Mean radius of a toroid is 10 cm and number of turns are 500. If current flowing through it is 0.1 ampere then value of magnetic field (in tesla) for toroid :- (1) 10–2 (2) 10–5 (3) 10–3 (4) 10–4 31. A long solenoid has length L, average diameter D and n layer of turns. Each layer contains N turns. If current flowing through the solenoid is i the value of magnetic field at the centre :- (1) Proportional to D (2) Inversely proportional to D (3) Does not depend on D (4) Proportional to L 32. A long solenoid carrying a current produces a magnetic field B along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is :- (1) B/2 (2) B (3) 2B (4) 4B 33. A long solenoid having 200 turns/cm and carries current i. Magnetic field at its axis is 6·28 × 10–2 wb/m2. An another solenoid having 100 turns/cm and carries i 3 current, then magnetic field at its axis will be :- (1) 1.05 × 10–4 Wb/m2 (2) 1.05 × 10–2 Wb/m2 (3) 1.05 × 10–5 Wb/m2 (4) 1.05 × 10–3 Wb/m2 i i i R C
NEET : Physics [ 96 ] www.allendigital.in  Digital MAGNETIC FORCE & MOVING CHARGE IN MAGNETIC FIELD 34. A proton and an alpha particle are separately projected in a region where a uniform magnetic field exists. The initial velocities are perpendicular to the direction of magnetic field. If both the particles move along circles of equal radii, the ratio of momentum of proton to alpha particle Pp P       is :- (1) 1 (2) 1/2 (3) 2 (4) 1/4 35. Cathode rays are moving between the poles of a magnet. Due to the effect of magnetic field of magnet :- (1) velocity of rays increases (2) velocity of rays decreases (3) rays deflected towards south pole (4) rays deflected in upward direction and perpendicular to the plane of the paper 36. Following charge has maximum frequency of rotation in uniform transverse magnetic field :- (1) a proton (2) an alpha particle (3) an electron (4) a neutron 37. Which of the following particle will experiences maximum magnetic force, when projected with the same velocity perpendicular to a magnetic field :- (1) electron (2) proton (3) He+ (4) Li++ 38. When  and  rays are subjected to a magnetic field which is perpendicular to the direction of their motion, with their same speed. The curvature of path of both the particles are :- (1) equal (2) more for  particles (3) more for  particles (4) none 39. Two identically charged particles A and B initially at rest, are accelerated by a common potential difference V. They enters into a uniform transverse magnetic field B and describe a circular path of radii r1 and r2 respectively then their mass ratio is :- (1) 2 1 2 r r       (2) 2 2 1 r r       (3) 1 2 r r       (4) 2 1 r r       40. An -particle experiences a force of 3.84×10–14 N when it moves perpendicular to magnetic field of 0.2 Wb/m2 then speed of the  - particle is :- (1) 6.0 × 105 m/sec (2) 5.0 × 105 m/sec (3) 1.2 × 106 m/sec (4) 3.8 × 106 m/sec 41. If an electron enters a magnetic field with its velocity pointing in the same direction as the magnetic field then :– (1) the electron will turn towards right (2) the electron will turn towards left (3) the velocity of the electron will increase (4) the velocity of the electron will remain unchanged 42. A charge having q/m equal to 108C/kg and with velocity 3 × 105 m/s enters into a uniform magnetic field B = 0.3T at an angle 30° with direction of field. Then radius will be :- (1) 0.01 cm (2) 0.5 cm (3) 1 cm (4) 2 cm 43. When a charged particle enters in a uniform magnetic field its kinetic energy :- (1) remains constant (2) increases (3) decreases (4) becomes zero 44. Two particles x and y have equal charges and possessing equal kinetic energy enter in a uniform magnetic field and describe circular path of radius of curvature r1 and r2 respectively. The ratio of their masses is :- (1) 1 2 r r       (2) 1/2 1 2 r r       (3) 2 1 2 r r       (4) 2 1 r r       N S