Tiêu đề 20. Magnetism And Matter.pdf ✅

1. A magnetised wire of moment M is bent into an arc of a circle subtending an angle of 60° at the centre; then the new magnetic moment is : (1) (2M/) (2) (M/) (3) (3 3 M/) (4) (3M/) 2. Which is incorrect? (1) The angle of dip at magnetic poles is 90° (2) Due to earth magnetic field cosmic articles which coming from space can never reach the magnetic equator. (3) At magnetic poles density of cosmic particles is maximum (4) Magnetic meridian is a straight line. 3. The coercive force for a certain permanent magnet is 4.0 × 104 A/m. This magnet is placed inside along solenoid of 40 turns/cm and a current is passed in the solenoid to demagnetise it completely. Find the current. (1) 1 A (2) 5 A (3) 10 A (4) 20 A 4. Relative magnetic permeability (μr) is negative for which of the following substances? (1) Dimagnetic (2) Paramagnetic (3) Ferromagnetic (4) None of these 5. A coil of area A = 0.5 m2 is situated in a uniform magnetic field B = 4.0 wb/m2 and area vector makes an angle of 60o with respect to the magnetic field as shown in figure. The value of the magnetic flux through the area A would be equal to 6. Magnets A and B are geometrically similar but the magnetic moment of A is twice that of B. IfT1 and T2 be the time periods of the oscillation when their like poles and unlike poles are kept together respectively, then 1 2 T T will be 7. At curie point, a ferro magnetic material becomes:- (1) Non magnetic (2) Diamagnetic (3) Paramagnetic (4) Strongly ferromagnetic 8. Dip angle are 30o & 45o at two different places, then ratio of horizontal component of earth magnetic field at these place will be :- 9. Consider the following figure, a uniform magnetic field of 0.2 T is directed along the positive x-axis. What is the magnetic flux through top surface of the figure (1) Zero (2) 0.8 m-wb (3) 1.0 m-wb (4) – 1.8 m-wb 10. Which of the following statements is correct for diamagnetic materials : (1) r< 1 (2)  is negative and low (3)  does not depend on temperature (4) All of the above 11. A super conductor exhibits perfect : (1) Ferromagnetism (2) Antiferromagnetism (3) Paramagnetism (4) Diamagnetism 12. Following figures show the arrangement of bar magnets in different configurations. Each magnet has magnetic dipole moment m . Which configuration has highest net magnetic dipole moment ? Magnetism and Matter
(1) (a) (2) (b) (3) (c) (4) (d) 13. A negative charge is given to a non- conducting loop and the loop is rotated in the plane of paper about its centre as shown in figure. The magnetic field produced by the ring affects a small magnet placed above the ring in the same plane :- (1) The magnet does not rotate (2) The magnet rotates clockwise as seen from below (3) The magnet rotates anticlockwise as seen from below (4) No effect on magnet is there 14. A magnet makes 40 oscillations per minute at a place having magnetic field of 0.1 × 10–5T. At another place, it takes 2.5 sec to complete one vibration. The value of earth's horizontal field at that place is : (1) 0.25 × 10–6 T (2) 0.36 × 10–6T (3) 0.66 × 10–8 T (4) 1.2 × 10–6T 15. If the dip circle is set at 45° to the magnetic meridian, then the apparent dip is 30°. The true dip. of the place is :- 16. The intensity of magnetisation I is plotted against the magnetising field H for different substances. The curves A and B shown in the adjoining figure are associated with :- (1) Soft iron and steel respectively (2) Steel and soft iron respectively (3) A diamagnetic and paramagnetic substance respectively (4) A paramagnetic and diamagnetic substance respectively 17. If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material are denoted by ,   d p and  f respectively, then :- (1) 0  p = and 0  f  (2) 0 d  and 0  p = (3) 0 d  and 0  f  (4) 0 d = and 0  p  18. There are four light-weight rod samples A,B,C D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted :- (i) A is feebly repelled (ii) B is feebly attracted (iii) C is strongly attracted (iv) D remains unaffected Which one of the following is true? (1) B is of a paramagnetic material (2) C is of a diamagnetic material (3) D is of a ferromagnetic material (4) A is of a non-magnetic material
19. A magnetic needle is kept in a non-uniform magnetic field. It experiences :- (1) A force and a torque (2) A force but not a torque (3) A torque but not a force (4) Neither a torque nor a force 20. Assertion :-At Curie temperature ferro magnetic material converts to paramagnetic material. Reason :-At Curie temperature exchange coupling collapse. (1) A (2) B (3) C (4) D 21. The real angle of dip, if a magnet is suspended at an angle of 30° to the magnetic meridian and the dip needle makes an angle of 45° with the horizontal is:- (1) 1 2 tan 3 −       (2) 1 3 tan 2 −         (3) ( ) 1 tan 3 − (4) 1 1 tan 3 −       22. Assertion :-Copper is a paramagnetic substance. Reason:-Paramagnetic substance when placed in a magnetic field are feebly magnetised in a direction opposite to that of the magnetising field. (1) A (2) B (3) C (4) D 23. When a magnet of vibration magnetometer heated, its magnetic moment decreases by 36%. The time period of oscillation :- (1) Increases by 25% (2) Decreases by 25% (3) Increases by 64% (4) Decreases by 64% 24. Which one of the following characteristics is not associated with a ferromagnetic material :- (1) It is strongly attracted by a magnet (2) It tends to move from a region of strong magnetic field to a region of weak magnetic field (3) Its origin is the spin of electrons (4) Above the Curie temperature, it exhibits paramagnetic properties 25. The time period of a vibration magnetometer isT0. Its magnet is replaced by another magnet whose moment of inertia is 3 times and magnetic moment is 1/3 of the initial magnet. The time period now will be :- (1) 3T0 (2) T0 (3) 0 T / 3 (4) T0/3 26. Curie temperature is the temperature above which:- (1) Paramagnetic material becomes ferromagnetic material. (2) Ferromagnetic material becomes diamagnetic material (3) Ferromagnetic material becomes paramagnetic material (4) Paramagnetic material becomes diamagnetic material 27. For shown situation of two dipoles the nature of forces between them are :- (I) (II) (1) attraction, attraction (2) attraction, repulsion (3) repulsion, repulsion (4) repulsion, attraction
28. Two identical short bar magnets, each having magnetic moment M, are placed a distance of 2dapart with axes perpendicular to each other in a horizontal plane. The magnetic induction at a point midway between them is :- (1) ( ) 0 3 2 4 M d   (2) ( ) 0 3 3 4 M d   (2) 0 3 2 M d         (4) ( ) 0 3 5 4 M d   29. The magnetic susceptibility of a paramagnetic substance at –73oC is 0.0060, then its value at– 173oC will be :- (1) 0.0030 (2) 0.0120 (3) 0.0180 (4) 0.0045 KEY 1 – 10 4 4 3 1 2 3 3 1 3 4 11 – 20 4 3 2 2 2 2 4 1 1 1 21 – 29 2 4 1 2 1 3 2 4 2 Hints & Solutions 1. 1 2 sin 2 M M         = 2. Conceptual 3. H nI = 0 4. Conceptual 5.   = BAcos 6. 1 T M  2 1 2 2 2 1 2 1 M M T M M T + = − 7. Conceptual 8. cos B B H =  9.   = BAcos 10. Conceptual 11. Conceptual 12. 2 cos 2 M M net  = 13. Conceptual 14. 1 2 MBH f  I = 15. 1 tan tan cos    = 16. Conceptual 17. Conceptual 18. Conceptual 19. Conceptual 20. Conceptual 21. 1 tan tan cos    = 22. Conceptual 23. I T M  2 1 1 2 1 100 1 100 T M T M         −  = −                24. Conceptual 25. I T M  26. Conceptual 27. Conceptual 28. 2 2 B B B = + a e 29. 1 T  