Tiêu đề 05. MAGNETISM and MATTER(H).pdf ✅

NEET REVISION 9. The length of a magnet is . Its pole strength is . When it is cut into four equal pieces parallel to its axis, the magnetic length, pole strength and moments of each piece are: (respectively) [Q360615] (1) (2) (3) (4) 10. A short bar magnet is oscillating in a magnetic field and its time period is 2 seconds. If another piece of brass of double moment of inertia be placed over that magnet the time period of that combination in that field is [Q360763] (1) (2) (3) 2 (4) 11. A sheet is placed on a horizontal surface in front of a strong magnetic pole. A force is needed to: A. hold the sheet there if it is magnetic. B. hold the sheet there if it is non-magnetic. C. move the sheet away from the pole with uni‐ form velocity if it is conducting. D. move the sheet away from the pole with uni‐ form velocity if it is both, non-conducting and non-polar. Choose the correct statement(s) from the options given below: [Q360577] (1) B and D only (2) A and C only (3) A, C and D only (4) C only 12. A thin rectangular magnet suspended freely has period of oscillation equal to . Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscil‐ late freely in the same field. If its period of oscil‐ lation is , then ratio is [Q360777] (1) 2 (2) (3) (4) 13. The curve for a ferromagnet is shown in the figure. The ferromagnet is placed inside a long solenoid with 1000 turns/ . The current that should be passsed in the solenoid to demag‐ netise the ferromagnet completely is: [Q360522] (1) (2) (3) (4) 14. The magnet of a vibration magnetometer is heated so as to reduce its magnetic moment by . By doing this the periodic time of the mag‐ netometer will [Q360793] (1) Increase by (2) Decrease by (3) Increase by (4) Decrease by 15. Assertion : Magnetism is relativistic. Reason : When we move along with the charge (like elec‐ tron with ) so that there is no motion relative to us, we find no magnetic field associ‐ ated with the charge. [Q360571] (1) Both Assertion and Reason are correct and Reason is the correct ex- planation of the Assertion. (2) Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion. (3) Assertion is correct but Reason is incorrect. (4) Assertion is incorrect but reason is correct. 16. Assume that each iron atom has a permanent magnetic moment of . The density of atoms in iron is . The maxi‐ mum magnetic field on the axis inside the cylinder. [Q360492] (1) 1 (2) 2 (3) 3 (4) 4 17. The work done in turning a magnet of magnetic moment by an angle of from the meridian is times the corresponding work done to turn it through an angle of : [Q360408] (1) (2) (3) (4) 18. Magnets and are geometrically similar but the magnetic moment of is twice that of . If and be the time periods of the oscillation when their like poles and unlike poles are kept 16 cm 250 mA. m 4 cm; 62.5 milli Am; 250 milli amp. cm2 8 cm; 500 milli Am; 400 milli amp. cm2 16 cm; 250 milli Am; 4000 milli amp. cm2 16 cm; 62.5 milli Am; 0.01A. m2 2√3s 2√2s s 1/√2s T T ′ T ′/T 1 2√2 1 2 1 4 B − H cm 2mA 20μA 1mA 40μA 19% 11% 19% 19% 21% 10 7 m/s 2μB (1μB = 9.27 × 10 −24Am−2) 8.52 × 10 28 m−3 B T T T T M 90 ∘ n 60 ∘ n = 1/2 n = 2 n = 1/4 n = 1 A B A B T1 T2
NEET REVISION together respectively, then will be [Q360767] (1) (2) (3) (4) 19. A bar magnet is demagnetized by inserting it in‐ side a solenoid of length 0.2 , 100 turns, and carrying a current of 5.2 . The coercivity of the bar magnet is [Q360519] (1) (2) (3) (4) 20. An example of a perfect diamagnet is a super‐ conductor. This implies that when a supercon‐ ductor is put in a magnetic field of intensity , the magnetic field inside the superconductor will be such that : [Q360469] (1) (2) (3) (4) 21. A long bar magnet has time period 2 in a vi‐ bration magnetometer. The magnet is cut along its length into 3 equal parts and the three parts are placed one over the other, like poles together. The time period of this combination will be : [Q360779] (1) 2 (2) (3) (4) 22. A rod of ferromagnetic material with dimen‐ sions is placed in a magnetic field of strength as a result of which a magnetic moment of is produced in the rod. The value of magnetic in‐ duction will be [Q360539] (1) (2) (3) (4) 23. Two bar magnets of the same masses, lengths and breadths but having magnetic moments and , are joined together pole to pole and sus‐ pended by a string. The time period of assembly in a magnetic field of strength is . If the po‐ larity of one of the magnets is reversed and com‐ bination is again made to oscillate in the same field, the time of oscillating is [Q360781] (1) (2) (3) (4) 24. A paramagnetic material has atoms/ . Its magnetic susceptibility at temperature 350 is . Its susceptibility at 300 is [Q360475] (1) (2) (3) (4) 25. The soft-iron is a suitable material for making an electromagnet. This is because soft-iron has: [Q360516] (1) Low coercivety and high retentivety (2) Low coercivety and low permeability (3) High permeability and low retentivety (4) High permeability and high retentivety 26. Two identical bar magnets each of magnetic moment , separated by some distance are kept perpendicular to each other. The magnetic induc‐ tion at a point at the same distance from the centre of magnets, is ( permeability of free space) [Q360629] (1) (2) (3) (4) 27. Match the Column I and Column II Choose the correct answer from the options given below : [Q360579] (1) A – R, B – S, C – P, D – Q (2) A – R, B – P, C – S, D – Q T1 T2 1 3 1 2 1 √3 √3 m A 520 A/m 1200 A/m 2600 A/m 285 A/m B Bs Bs < B but Bs ≠ 0 Bs = B Bs = 0 Bs = −B s s s 2 3 2√3 s s 3 2 10 cm × 0.5 cm × 0.2 cm 0.5 × 10 4amp/m 5 amp m2 0.54 T 0.358 T 2.519 T 6.28 T m 2m H 3s √3s 3√3s 3s 6s 10 28 m3 K 2.8 × 10 −4 K 3.267 × 10 −4 3.672 × 10 −4 2.672 × 10 −4 3.726 × 10 −4 M d μ0 = (√3) μ0 4π M d3 (√2) μ0 4π M d3 (√5) μ0 4π M d3 2μ0 π M d3
NEET REVISION (3) A – S, B – P, C – R, D – Q (4) A – P, B – R, C – Q, D – S 28. The dipole moment of each molecule of param‐ agnetic gas is . The temperature of gas is and the number of molecules per unit volume in it is . The maxi‐ mum possible intensity of magnetisation in the gas will be (in ) is [Q360550] (1) (2) (3) (4) 29. The magnetic moment of a bar magnet is 0.256 amp. . Its pole strength is 400 milli amp.m. It is cut into two equal pieces and these two pieces are arranged at right angles to each with their un‐ like poles in contact (or like poles in contact). The resultant magnetic moment of the system is [Q360624] (1) (2) (3) (4) 30. An iron ring of mean radius 0.25 and cross‐ sectional area is wound uni‐ formly with 1500 turns of wire. A current of 5 is set up in the wire. If relative permeability of iron is 1500 the magnetic flux density of the ring is [Q360648] (1) 4.5 (2) 3 (3) 9 (4) None of these 31. The mathematical equation for magnetic field lines of force is [Q360575] (1) (2) (3) (4) 32. The dipole moment associated with an iron atom in an iron bar is . Assume the bar is 5 long, has cross-sectional area of and all iron atoms have their dipole mo‐ ment aligned. The dipole moment of the bar is [density [Q360599] (1) (2) (3) (4) None of these 33. Assertion : A device for storing memory displays a hystere‐ sis loop such as by a ferromagnetic substance. Reason : Ferromagnetic substances are those in which each individual atom has a non zero magnetic moment. [Q360514] (1) Both Assertion and Reason are correct and Reason is the correct ex- planation of the Assertion. (2) Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion. (3) Assertion is correct but Reason is incorrect. (4) Assertion is incorrect but reason is correct. 34. Two identical short bar magnets are arranged as shown in figure. The resultant induction at cor‐ ner is [Q360625] (1) (2) (3) (4) 35. In a uniform magnetic field of , a mag‐ netic needle performs 20 complete oscillations in 5 seconds as shown. The moment of inertia of the needle is . If the magnitude of magnetic moment of the needle is , then the value of ' ' is : [Q360776] (1) (2) (3) (4) 36. Rate of change of torque with deflection is maximum for a magnet suspended freely in a uniform magnetic field of induction , when [Q360422] (1) (2) (3) (4) 37. A short bar magnet is placed in the magnetic meridian of the earth with north pole pointing north. Neutral points are found at a distance of 30 from the magnet on the East-West line, drawn through the middle point of the magnet. The magnetic moment of the magnet in is close to: (Given in SI units and Horizontal component of earth's magnetic field tesla) [Q360706] (1) 14.6 (2) 19.4 (3) 9.7 (4) 4.9 38. A bar magnet of magnetic moment ' ' is bent in the form of an arc which makes angle . The percentage change in the magnetic moment is [Q360595] 1.5 × 10 −23 Am2 27 ∘C 2 × 10 26 m−3 A/m 3 × 10 3 4 × 10 −3 5 × 10 5 6 × 10 −4 m2 √2 × 256 × 10 −3 Am2 250 × 10 −3 Am2 × 10 −3 256 Am2 √2 × 10 −3 128 Am2 √2 m 7.4 × 10 −4 m2 A T T T ∇ ⋅ B = 0 ∇ ⋅ B ≠ 0 ∇ ⋅ B > 0 ∇ ⋅ B < 0 1.8 × 10 −23Am2 cm 1 cm2 = 7.8 g/cc] 6.6A. m2 5.6 A. m2 7.6A. m2 B μo 4π 3M d 3 μo 4π 2M d 3 μo 4π M d 3 μo 4π 4M d 3 0.049T 9.8 × 10 −6 kg m2 x × 10 −5Am 2 x 5 π 2 128 π 2 50 π 2 1280 π 2 τ θ B θ = 0 ∘ θ = 45 ∘ θ = 60 ∘ θ = 90 ∘ cm Am2 = 10 −7 μ0 4π BH = = 3.6 × 10 −5 M 60 ∘