Permanent Magnets
OBJECTIVE-II
1. Pick the correct options.
(a) Magnetic field is produced by electric charges only.
(b) Magnetic poles are only mathematical assumptions having no real existence.
(c) A north pole is equivalent to a clockwise current and a south pole is equivalent to an anticlockwise current.
(d) A bar magnet is equivalent to a long, straight current.
ANSWER: (a), (b).
Explanation: Magnetic field is produced by moving charges only. Even in permanent magnets, the magnetic properties come from the moving charges at atomic levels. (a) is correct.
The magnetic poles are mathematical assumptions to study the magnetic effects. And we call a positive magnetic charge the North Pole and a negative magnetic charge the south pole. Option (b) is also correct.
(c) is not correct because a north pole is equivalent to an anticlockwise current and a south pole is equivalent to a clockwise current.
Option (d) is also not correct because a bar magnet is not equivalent to a long, straight current because the magnetic fields produced by them are different.
2. A horizontal circular loop carries a current that looks clockwise when viewed from above. It is replaced by an equivalent magnetic dipole consisting of a south pole S and a north pole N.
(a) The line SN should be along the diameter of the loop.
(b) The line SN should be perpendicular to the plane of the loop.
(c) The south pole should be below the loop.
(d) The north pole should be below the loop.
ANSWER: (b), (d).
Explanation: If a circular loop is replaced by an equivalent magnetic dipole, then the SN line should be perpendicular to the plane of the loop. It is because the north pole is towards the side from which the current in the loop is anticlockwise and the south pole is to that side from which the current in the loop is viewed clockwise. Hence only the options (b) and (d) are correct.
3. Consider a magnetic dipole kept in the north-south direction. Let P₁, P₂, Q₁, Q₂ be four points at the same distance from the dipole towards the north, south, east, and west of the dipole respectively. The directions of the magnetic field due to the dipole are the same at
(a) P₁ and P₂
(b) Q₁ and Q₂
(c) P₁ and Q₁
(d) P₂ and Q₂
ANSWER: (a), (b).
Explanation: The points P₁ and P₂ are equidistant from the dipole on both sides of its axis. At P₁, the direction of the field will be from the dipole towards the north pole. Similarly at P₂, the direction of the field will also be towards the north and the south end of the dipole. Option (a) is correct.
Q₁ and Q₂ are symmetrical points on both sides of the perpendicular bisector of the dipole. Hence the directions of the magnetic field will also be the same at these points. The direction will be from north to south. Hence the option (b) is also correct.
The directions of the field at points in options (c) and (d) are opposite to each other. Hence not correct.
4. Consider the situation of the previous problem. The directions of the magnetic field due to the dipole are opposite at
(a) P₁ and P₂
(b) Q₁ and Q₂
(c) P₁ and Q₁
(d) P₂ and Q₂
ANSWER: (c), (d).
Explanation: As we can see in the diagram below, 
Diagram for Q-4
at points P₁ and Q₁ the directions of the magnetic field are opposite. Also at points P₂ and Q₂ the directions are opposite. Hence only options (c) and (d) are correct.
5. To measure the magnetic moment of a bar magnet, one may use
(a) a tangent galvanometer
(b) a deflection galvanometer if the earth's horizontal field is known
(c) an oscillation magnetometer if the earth's horizontal field is known
(d) both deflection and oscillation magnetometer if the earth's horizontal field is not known.
ANSWER: (b), (c), (d).
Explanation: To measure the magnetic moment of a bar magnet we can measure M/BH using a deflection magnetometer or MBH using an oscillation magnetometer if we know BH. Hence options (b), (c) and (d) are correct not option (a).
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Links to the Chapters
Links to the Chapters
CHAPTER- 36- Permanent Magnets
CHAPTER- 35- Magnetic Field due to a Current
CHAPTER- 34- Magnetic Field
CHAPTER- 33- Thermal and Chemical Effects of Electric Current
CHAPTER- 36- Permanent Magnets
CHAPTER- 35- Magnetic Field due to a Current
CHAPTER- 34- Magnetic Field
CHAPTER- 33- Thermal and Chemical Effects of Electric Current
CHAPTER- 32- Electric Current in ConductorsCHAPTER- 31- CapacitorsCHAPTER- 30- Gauss's Law
CHAPTER- 29- Electric Field and Potential
CHAPTER- 28- Heat Transfer
OBJECTIVE -I
CHAPTER- 26-Laws of Thermodynamics
CHAPTER- 25-CALORIMETRY
Questions for Short Answer
OBJECTIVE-I
OBJECTIVE-II
EXERCISES - Q-11 to Q-18
CHAPTER- 24-Kinetic Theory of Gases
CHAPTER- 23 - Heat and Temperature
CHAPTER- 21 - Speed of Light
CHAPTER- 20 - Dispersion and Spectra
CHAPTER- 19 - Optical Instruments
CHAPTER- 18 - Geometrical Optics
CHAPTER- 17 - Light Waves
CHAPTER- 16 - Sound Waves
CHAPTER- 15 - Wave Motion and Waves on a String
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
CHAPTER- 11 - Gravitation
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 32- Electric Current in Conductors
CHAPTER- 31- Capacitors
CHAPTER- 30- Gauss's Law
CHAPTER- 29- Electric Field and Potential
CHAPTER- 28- Heat Transfer
CHAPTER- 26-Laws of Thermodynamics
CHAPTER- 25-CALORIMETRY
Questions for Short Answer
OBJECTIVE-I
OBJECTIVE-II
CHAPTER- 24-Kinetic Theory of Gases
CHAPTER- 23 - Heat and Temperature
CHAPTER- 21 - Speed of Light
CHAPTER- 20 - Dispersion and Spectra
CHAPTER- 19 - Optical Instruments
CHAPTER- 18 - Geometrical Optics
CHAPTER- 17 - Light Waves
CHAPTER- 16 - Sound Waves
CHAPTER- 15 - Wave Motion and Waves on a String
CHAPTER- 14 - Fluid Mechanics
CHAPTER- 13 - Fluid Mechanics
CHAPTER- 12 - Simple Harmonic Motion
CHAPTER- 11 - Gravitation
CHAPTER- 10 - Rotational Mechanics
CHAPTER- 9 - Center of Mass, Linear Momentum, Collision
CHAPTER- 8 - Work and Energy
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CHAPTER- 7 - Circular Motion
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CHAPTER- 6 - Friction
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CHAPTER- 6 - Friction
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CHAPTER- 5 - Newton's Laws of Motion
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Click here for→Newton's Laws of Motion,Exercises(Q.No. 13 to 27)
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CHAPTER- 4 - The Forces
The Forces-
"Questions for short Answers"
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CHAPTER- 3 - Kinematics - Rest and Motion
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CHAPTER- 2 - "Physics and Mathematics"
CHAPTER- 2 - "Physics and Mathematics"
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