STD 12 - Magnetism and matter PYQs: JEE Mains Physics

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1. 1. A short bar magnet placed with its axis at \(30^{\circ}\) with an external field of 800 Gauss, experiences a torque of \(0.016 N . m\). The work done in moving it from most stable to most unstable position is \(\alpha \times 10^{-3} J\). The value of \(\alpha\) is _________ . 2026 Medium
2. 2. A solenoid has a core made of material with relative permeability \(400\). The magnetic field produced in the interior of solenoid is \(1.0\) T. The magnetic intensity in SI units is \(\alpha \times 10^5\). The value of \(\alpha\) is ______.
   (Free space permeability \(\mu_0=4\pi \times 10^{-7}\) SI units.) 2026 Medium
3. 3. Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Consider a ferromagnetic material :
   Assertion (A) : The individual atoms in a ferromagnetic material possess a magnetic dipole moment and interact with one another in such a way that they spontaneously align themselves forming domains.
   Reason (R) : At high enough temperature, the domain structure of ferromagnetic material disintegrates. Thus, magnetization will disappear at high enough temperature known as Curie temperature.
   In the light of the above statements, choose the correct answer from the options given below : 2026 Hard
4. 4. Two identical small bar magnets each of dipole moment \(3\sqrt{5}\) J/T are placed at a center to center separation of \(10\) cm, with their axes perpendicular to each other as shown in figure. The value of magnetic field at the point P midway between the magnets is \(\alpha \times 10^{-3}\) T. The value of \(\alpha\) is ______.
   (\(\mu_0=4\pi \times 10^{-7}\) Tm/A)
   2026 Hard
5. 5.
   A bar magnet has total length \(2 l=20\) units and the field point \(P\) is at a distance \(\mathrm{d}=10\) units from the centre of the magnet. If the relative uncertainty of length measurement is \(1 \%\), then uncertainty of the magnetic field at point P is : 2025 Hard
6. 6. A magnetic dipole experiences a torque of \(80 \sqrt{3} \mathrm{~N} \mathrm{~m}\) when placed in uniform magnetic field in such a way that dipole moment makes angle of \(60^{\circ}\) with magnetic field. The potential energy of the dipole is : 2025 Easy
7. 7. Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason(R).
   Assertion (A) : Magnetic monopoles do not exist.
   Reason (R) : Magnetic field lines are continuous and form closed loops.
   In the light of the above statements, choose the most appropriate answer from the options given below : 2025 Easy
8. 8. The percentage increase in magnetic field (B) when space within a current carrying solenoid is filled with magnesium (magnetic susceptibility \(\left.\chi_{\mathrm{mg}}=1.2 \times 10^{-5}\right)\) is : 2025 Medium
9. 9. The relationship between the magnetic susceptibility \((\chi)\) and the magnetic permeability \((\mu)\) is given by :
   (\(\mu_0\) is the permeability of free space and \(\mu_{\mathrm{r}}\) is relative permeability) 2025 Easy
10. 10. A straight magnetic strip has a magnetic moment of \(44 \mathrm{Am}^2\). If the strip is bent in a semicircular shape, its magnetic moment will be _______\(\mathrm{Am}^2\) \(\left(\right.\) Given \(\left.\pi=\frac{22}{7}\right)\) 2024 Hard
11. 11. Paramagnetic substances: \(A\). align themselves along the directions of external magnetic field. \(B\). attract strongly towards external magnetic field. \(C\). has susceptibility little more than zero. \(D\). move from a region of strong magnetic field to weak magnetic field. Choose the most appropriate answer from the options given below: 2024 Hard
12. 12. The coercivity of a magnet is \(5 \times 10^3 \mathrm{~A} / \mathrm{m}\). The amount of current required to be passed in a solenord of length \(30 \mathrm{~cm}\) and the number of turns \(150\) , so that the magnet gets demagnetised when inside the solenoid is _______ A. 2024 Hard
13. 13. The magnetic potential due to a magnetic dipole at a point on its axis situated at a distance of \(20 \mathrm{~cm}\) from its center is \(1.5 \times 10^{-5} \  \mathrm{Tm}\). The magnetic moment of the dipole is _______ \(\mathrm{Am}^2\). (Given : \(\frac{\mu_0}{4 \pi}=10^{-7} \  \mathrm{TmA}^{-1}\) ) 2024 Hard
14. 14. A bar magnet with a magnetic moment \(5.0\,Am ^2\) is placed in parallel position relative to a magnetic field of \(0.4\,T\). The amount of required work done in turning the magnet form parallel to antiparallel position relative to the field direction is \(.........\,J\) 2023 Medium
15. 15. A solenoid of \(1200\) turns is wound uniformly in a single layer on a glass tube \(2\,m\) long and \(0.2\,m\) in diameter. The magnetic intensity at the center of the solenoid when a current of \(2\,A\) flows through it is: 2023 Easy
16. 16. Given below are two statements; one is labelled as Assertion \(A\) and the other is labelled as Reason \(R\). Assertion \(A:\) Electromagnets are made of soft iron. Reason \(R:\) Soft iron has high permeability and low retentivity. In the light of above, statements, choose the most appropriate answer from the options given below. 2023 Medium
17. 17. Given below are two statements: Statement \(I:\) For diamagnetic substance \(-1 \leq \chi < 0\), where \(\chi\) is the magneticsusceptibility. Statement \(II:\) Diamagnetic substances when placed in an external magnetic field, tend to move from stronger to weaker part of the field. In the light of the above statements, choose the correct answer from the options given below. 2023 Medium
18. 18. Given below are two statements: Statement \(I\) : The diamagnetic property depends on temperature. Statement \(II\) : The included magnetic dipole moment in a diamagnetic sample is always opposite to the magnetizing field. In the light of given statement, choose the correct answer from the options given below: 2023 Medium
19. 19. The current required to be passed through a solenoid of \(15\,cm\) length and 60 turns in order to demagnetise a bar magnet of magnetic intensity \(2.4 \times 10^3\,Am ^{-1}\) is \(.........A\). 2023 Medium
20. 20. The magnetic intensity at the centre of a long current carrying solenoid is found to be \(1.6 \times 10^3 Am ^{-1}\). If the number of turns is 8 per cm, then the current flowing through the solenoid is \(................\,A\) 2023 Easy
21. 21. A bar magnet having a magnetic moment of \(2.0 \times\) \(10^{5} \; JT ^{-1}\), is placed along the direction of uniform magnetic field of magnitude \(B =14 \times 10^{-5}\; T\). The work done in rotating the magnet slowly through \(60^{\circ}\) from the direction of field is .............. \(J\)  2022 Medium
22. 22. A compass needle of oscillation magnetometer oscillates \(20\) times per minute at a place \(P\) of dip \(30^{\circ}\). The number of oscillations per minute become \(10\) at another place \(Q\) of \(60^{\circ} dip\). The ratio of the total magnetic field at the two places \(\left(B_{Q}: B_{p}\right)\) is. 2022 Hard
23. 23. A magnet hung at \(45^{\circ}\) with magnetic meridian makes an angle of \(60^{\circ}\) with the horizontal. The actual value of the angle of dip is. 2022 Medium
24. 24. At a certain place the angle of dip is \(30^{\circ}\) and the horizontal component of earth's magnetic field is \(0.5 G\). The earth's total magnetic field (in \(G\) ), at that certain place, is ................ 2022 Easy
25. 25. Given below are two statements: Statement\(- I\) : Susceptibilities of paramagnetic and ferromagnetic substances increase with decrease in temperature. Statement\(- II\): Diamagnetism is a result of orbital motions of electrons developing magnetic moments opposite to the applied magnetic field. Choose the \(CORRECT\) answer from the options given below : - 2022 Medium
26. 26. The susceptibility of a paramagnetic material is \(99\) . The permeability of the material in \(Wb / A - m\) is : [Permeability of free space \(\left.\mu_{0}=4 \pi \times 10^{-7} Wb / A -m\right]\) 2022 Medium
27. 27. The vertical component of the earth's magnetic field is \(6 \times 10^{-5} T\) at any place where the angle of dip is \(37^{\circ}\). The earth's resultant magnetic field at that place will be \(\left(\right.\) Given \(\left.\tan 37^{\circ}=\frac{3}{4}\right)\) 2022 Easy
28. 28. Two bar magnets oscillate in a horizontal plane in earth's magnetic field with time periods of \(3\,s\) and \(4\,s\) respectively. If their moments of inertia are in the ratio of \(3: 2\) then the ratio of their magnetic moments will e. 2022 Medium
29. 29. A bar magnet of length \(14 \,cm\) is placed in the magnetic meridian with its north pole pointing towards the geographic north pole. A neutral point is obtained at a distance of \(18\, cm\) from the center of the magnet. If \(B _{ H }=0.4 \,G ,\) the magnetic moment of the magnet is \(\left(1\, G =10^{-4} T \right)\) 2021 Hard
30. 30. A long solenoid with \(1000\, turns/m\) has a core material with relative permeability \(500\) and volume \(10^{3}\, {cm}^{3} .\) If the core material is replaced by another material having relative permeability of \(750\) with same volume maintaining same current of \(0.75\, {A}\) in the solenoid, the fractional change in the magnetic moment of the core would be approximately \(\left(\frac{{x}}{499}\right) .\) Find the value of \({x}\). 2021 Hard
31. 31. A soft ferromagnetic material is placed in an external magnetic field. The magnetic domains: 2021 Medium
32. 32. At an angle of \(30^{\circ}\) to the magnetic meridian, the apparent dip is \(45^{\circ} .\) Find the true dip : 2021 Medium
33. 33. Choose the correct option: 2021 Medium
34. 34. Following plots show Magnetization \((M)\) \(vs\) Magnetising field \((H)\) and Magnetic susceptibility \((\chi)\) vs temperature \((T)\) graph : Which of the following combination will be represented by a diamagnetic material?
    2021 Medium
35. 35. In a ferromagnetic material, below the curie temperature, a domain is defined as: 2021 Medium
36. 36. In a uniform magnetic field, the magnetic needle has a magnetic moment \(9.85 \times 10^{-2} \,{A} / {m}^{2}\) and moment of inertia \(5 \times 10^{-6} \,{kgm}^{2}\). If it performs \(10\) complete oscillations in \(5\, seconds\) then the magnitude of the magnetic field is \(....\,mT.\) [ Take \(\pi^{2}\) as \(9.85\) ] 2021 Medium
37. 37. Statement \(I :\) The ferromagnetic property depends on temperature. At high temperature, ferromagnet becomes paramagnet. Statement \(II :\) At high temperature, the domain wall area of a ferromagnetic substance increases. In the light of the above statements, choose the most appropriate answer from the options given below : 2021 Medium
38. 38. The magnetic susceptibility of a material of a rod is \(499 .\) Permeability in vaccum is \(4 \pi \times 10^{-7}\; {H} / {m}\). Absolute permeability of the material of the rod is \(....\,\pi \times 10^{-4} {H} / {m}\) 2021 Medium
39. 39. The value of aluminium susceptibility is \(2.2 \times 10^{-5}\). The percentage increase in the magnetic field if space within a current carrying toroid is filled with aluminium is \(\frac{x}{10^{4}}\). Then the value of \(x\) is ...... . 2021 Hard
40. 40. Two short magnetic dipoles \({m}_{1}\) and \({m}_{2}\) each having magnetic moment of \(1\, {Am}^{2}\) are placed at point \({O}\) and \(P\) respectively. The distance between \(OP\) is \(1\, meter.\) The torque experienced by the magnetic dipole \({m}_{2}\) due to the presence of \({m}_{1}\) is ...... \(\times 10^{-7}\, {Nm}\)
    2021 Medium
41. 41. Which of the following statements are correct? \((A)\) Electric monopoles do not exist whereas magnetic monopoles exist. \((B)\) Magnetic field lines due to a solenoid at its ends and outside cannot be completely
    straight and confined. \((C)\) Magnetic field lines are completely confined within a toroid. \((D)\) Magnetic field lines inside a bar magnet are not parallel. \((E)\) \(\chi=-1\) is the condition for a perfect diamagnetic material, where \(\chi\) is its
    magnetic susceptibility. Choose the correct answer from the options given below: 2021 Medium
42. 42. A paramagnetic sample shows a net magnetisation of \(6 \,A / m\) when it is placed in an external magnetic field of \(0.4 \,T\) at a temperature of \(4\, K\). When the sample is placed in an external magnetic field of \(0.3\, T\) at a temperature of \(24\, K\), then the magnetisation will be\(......A/m\) 2020 Medium
43. 43. A perfectly dimagnetic sphere has a small spherical cavity at its centre, which is filled with a paramagnetic substance. The whole system is placed in a uniform magnetic field \(\overrightarrow{ B }\). Then the field inside the paramagnetic substance is:
    2020 Medium
44. 44. A small bar magnet placed with its axis at \(30^{\circ}\) with an external field of \(0.06\, T\) experiences a torque of \(0.018\, Nm\). The minimum work required to rotate it from its stable to unstable equilibrium position is 2020 Hard
45. 45. An iron rod of volume \(10^{-3}\, m ^{3}\) and relative permeability \(1000\) is placed as core in a solenoid with \(10\) \(turns/cm.\) If a current of \(0.5\, A\) is passed through the solenoid, then the magnetic moment of the rod will be\(...........Am^2\) 2020 Medium
46. 46. Magnetic materials used for making permanent magnets \((P)\) and magnets in a transformer \((T)\) have different properties of the following, which property best matches for the type of magnet required \(?\) 2020 Medium
47. 47. The figure gives experimentally measured \(\mathrm{B}\) vs. \(H\) variation in a ferromagnetic material. The retentivity, co-ercivity and saturation. respectively, of the material are
    2020 Medium
48. 48. A bar magnet is demagnetized by inserting it inside a solenoid of length \(0.2\, m\), \(100\, turns\), and carrying a current of \(5.2\, A\). The coercivity of the bar magnet is.....\(A/m\) 2019 Medium
49. 49. A hoop and a solid cylinder of same mass and radius are made of a permanent magnetic material with their magnetic moment parallel to their respective axes. But the magnetic moment of hoop is twice of solid cylinder. They are placed in a uniform magnetic field in such a manner that their magnetic moments make a small angle with the field. If the oscillation periods of hoop and cylinder are \(T_h\) and \(T_c\) respectively, then the relation between them is.... 2019 Medium
50. 50. A magnet of total magnetic moment \({10\,^{ - 2}}\hat i\,A - {m^2}\) is placed in a time varying magnetic field, \(B\,\hat i\,\left( {\cos \,\omega t} \right)\) where \(B = 1\, Tesla\) and \(\omega  = 0.125\, rad/s\). The work done for reversing the direction of the magnetic moment at \(t = 1\, second\), is 2019 Medium

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