A bar magnet's external field is strikingly similar to that of a finite current-carrying solenoid — the comparison is what suggested to Ampere that magnetism is fundamentally the effect of circulating currents, with no need for isolated magnetic charges. Just as a solenoid of turns, area and current is assigned a dipole moment , a bar magnet is assigned a **magnetic dipole
Magnetism and Matter
Class 126 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Bar magnet and magnetic field lines
Exam focus: Magnetic field lines always form closed loops with no start or end point, since isolated magnetic poles don't exist — unlike electric field lines, which begin and end on charges. A bar magnet's field falls off as 1/r³, its axial value twice the equatorial one.
Bar Magnet, Field Lines and Dipole Moment
Physics Wallah - Alakh Pandey
Dedicated single-concept lecture, first in the series; covers field lines and bar-magnet-in-field behaviour fully.
PhysicsNEET 2024show ▾An iron bar of length has magnetic moment . It is bent at the middle of its length such that the two arms make an angle of with each other. The magnetic moment of this new magnet is:
- A.✓
- B.
- C.
- D.
Solution
Bending does not change the pole strength ; it changes the distance between the poles. The two end poles are now separated by the chord of two arms of length at : . So .
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Save for spaced revision (free account)PhysicsNEET 2024show ▾In a uniform magnetic field of 0.049 T, a magnetic needle performs 20 complete oscillations in 5 seconds. The moment of inertia of the needle is . If the magnitude of the magnetic moment of the needle is , then the value of is:
- A.
- B.
- C.✓
- D.
Solution
Oscillation period s. For a magnetic needle, , so . Hence .
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Save for spaced revision (free account)PhysicsNEET 2023show ▾The net magnetic flux through any closed surface is:
- A.Zero✓
- B.Positive
- C.Infinity
- D.Negative
The worked solution is part of a paid pack.
2. Earth's magnetism
Exam focus: Dip angle is 0° at the magnetic equator, where the field is purely horizontal, and 90° at the magnetic poles, where it's purely vertical — and Earth's actual magnetic south pole sits near the geographic north.
Earth's Magnetism: Declination and Dip
Physics Wallah - Alakh Pandey
Directly matches the subtopic — angle of dip and angle of declination.
PhysicsNEET 2019show ▾At a point A on the earth's surface the angle of dip is . At a point B on the earth's surface the angle of dip is . We can interpret that:
- A.A and B are both located in the northern hemisphere
- B.A is located in the southern hemisphere and B is located in the northern hemisphere
- C.A is located in the northern hemisphere and B is located in the southern hemisphere✓
- D.A and B are both located in the southern hemisphere
The worked solution is part of a paid pack.
3. Dia-, para- and ferromagnetism
Exam focus: Diamagnetism is present in every material, including paramagnetic and ferromagnetic ones — it's just too weak to notice once a stronger attractive effect is present. Above its Curie temperature, a ferromagnetic material loses its domains and simply becomes paramagnetic.
Diamagnetism, Paramagnetism and Ferromagnetism
Physics Wallah - Alakh Pandey
Directly matches the subtopic, covering magnetisation, magnetic intensity, and the cause of dia/para/ferromagnetism.
PhysicsNEET 2024show ▾Match List I with List II.
List I (Material) List II (Susceptibility ) A. Diamagnetic I. B. Ferromagnetic II. C. Paramagnetic III. D. Non-magnetic IV. (a small positive number)
Choose the correct answer from the options given below:
- A.A-II, B-I, C-III, D-IV
- B.A-III, B-II, C-I, D-IV
- C.A-IV, B-III, C-II, D-I
- D.A-II, B-III, C-IV, D-I✓
Solution
Diamagnetic: small negative susceptibility, (II). Ferromagnetic: (III). Paramagnetic: small positive, (IV). Non-magnetic: (I).
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