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1
4290-4293
This is unlike the electric dipole where these field lines begin from a positive charge and end on the negative charge or escape to infinity FIGURE 5 1 The arrangement of iron filings surrounding a bar magnet The pattern mimics magnetic field lines
1
4291-4294
FIGURE 5 1 The arrangement of iron filings surrounding a bar magnet The pattern mimics magnetic field lines The pattern suggests that the bar magnet is a magnetic dipole
1
4292-4295
1 The arrangement of iron filings surrounding a bar magnet The pattern mimics magnetic field lines The pattern suggests that the bar magnet is a magnetic dipole * In some textbooks the magnetic field lines are called magnetic lines of force
1
4293-4296
The pattern mimics magnetic field lines The pattern suggests that the bar magnet is a magnetic dipole * In some textbooks the magnetic field lines are called magnetic lines of force This nomenclature is avoided since it can be confusing
1
4294-4297
The pattern suggests that the bar magnet is a magnetic dipole * In some textbooks the magnetic field lines are called magnetic lines of force This nomenclature is avoided since it can be confusing Unlike electrostatics the field lines in magnetism do not indicate the direction of the force on a (moving) charge
1
4295-4298
* In some textbooks the magnetic field lines are called magnetic lines of force This nomenclature is avoided since it can be confusing Unlike electrostatics the field lines in magnetism do not indicate the direction of the force on a (moving) charge Rationalised 2023-24 Physics 138 FIGURE 5
1
4296-4299
This nomenclature is avoided since it can be confusing Unlike electrostatics the field lines in magnetism do not indicate the direction of the force on a (moving) charge Rationalised 2023-24 Physics 138 FIGURE 5 3 Calculation of (a) The axial field of a finite solenoid in order to demonstrate its similarity to that of a bar magnet
1
4297-4300
Unlike electrostatics the field lines in magnetism do not indicate the direction of the force on a (moving) charge Rationalised 2023-24 Physics 138 FIGURE 5 3 Calculation of (a) The axial field of a finite solenoid in order to demonstrate its similarity to that of a bar magnet (b) A magnetic needle in a uniform magnetic field B
1
4298-4301
Rationalised 2023-24 Physics 138 FIGURE 5 3 Calculation of (a) The axial field of a finite solenoid in order to demonstrate its similarity to that of a bar magnet (b) A magnetic needle in a uniform magnetic field B The arrangement may be used to determine either B or the magnetic moment m of the needle
1
4299-4302
3 Calculation of (a) The axial field of a finite solenoid in order to demonstrate its similarity to that of a bar magnet (b) A magnetic needle in a uniform magnetic field B The arrangement may be used to determine either B or the magnetic moment m of the needle (ii) The tangent to the field line at a given point represents the direction of the net magnetic field B at that point
1
4300-4303
(b) A magnetic needle in a uniform magnetic field B The arrangement may be used to determine either B or the magnetic moment m of the needle (ii) The tangent to the field line at a given point represents the direction of the net magnetic field B at that point (iii) The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B
1
4301-4304
The arrangement may be used to determine either B or the magnetic moment m of the needle (ii) The tangent to the field line at a given point represents the direction of the net magnetic field B at that point (iii) The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B In Fig
1
4302-4305
(ii) The tangent to the field line at a given point represents the direction of the net magnetic field B at that point (iii) The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B In Fig 5
1
4303-4306
(iii) The larger the number of field lines crossing per unit area, the stronger is the magnitude of the magnetic field B In Fig 5 2(a), B is larger around region ii than in region i
1
4304-4307
In Fig 5 2(a), B is larger around region ii than in region i (iv) The magnetic field lines do not intersect, for if they did, the direction of the magnetic field would not be unique at the point of intersection
1
4305-4308
5 2(a), B is larger around region ii than in region i (iv) The magnetic field lines do not intersect, for if they did, the direction of the magnetic field would not be unique at the point of intersection One can plot the magnetic field lines in a variety of ways
1
4306-4309
2(a), B is larger around region ii than in region i (iv) The magnetic field lines do not intersect, for if they did, the direction of the magnetic field would not be unique at the point of intersection One can plot the magnetic field lines in a variety of ways One way is to place a small magnetic compass needle at various positions and note its orientation
1
4307-4310
(iv) The magnetic field lines do not intersect, for if they did, the direction of the magnetic field would not be unique at the point of intersection One can plot the magnetic field lines in a variety of ways One way is to place a small magnetic compass needle at various positions and note its orientation This gives us an idea of the magnetic field direction at various points in space
1
4308-4311
One can plot the magnetic field lines in a variety of ways One way is to place a small magnetic compass needle at various positions and note its orientation This gives us an idea of the magnetic field direction at various points in space 5
1
4309-4312
One way is to place a small magnetic compass needle at various positions and note its orientation This gives us an idea of the magnetic field direction at various points in space 5 2
1
4310-4313
This gives us an idea of the magnetic field direction at various points in space 5 2 2 Bar magnet as an equivalent solenoid In the previous chapter, we have explained how a current loop acts as a magnetic dipole (Section 4
1
4311-4314
5 2 2 Bar magnet as an equivalent solenoid In the previous chapter, we have explained how a current loop acts as a magnetic dipole (Section 4 10)
1
4312-4315
2 2 Bar magnet as an equivalent solenoid In the previous chapter, we have explained how a current loop acts as a magnetic dipole (Section 4 10) We mentioned Ampere’s hypothesis that all magnetic phenomena can be explained in terms of circulating currents
1
4313-4316
2 Bar magnet as an equivalent solenoid In the previous chapter, we have explained how a current loop acts as a magnetic dipole (Section 4 10) We mentioned Ampere’s hypothesis that all magnetic phenomena can be explained in terms of circulating currents FIGURE 5
1
4314-4317
10) We mentioned Ampere’s hypothesis that all magnetic phenomena can be explained in terms of circulating currents FIGURE 5 2 The field lines of (a) a bar magnet, (b) a current-carrying finite solenoid and (c) electric dipole
1
4315-4318
We mentioned Ampere’s hypothesis that all magnetic phenomena can be explained in terms of circulating currents FIGURE 5 2 The field lines of (a) a bar magnet, (b) a current-carrying finite solenoid and (c) electric dipole At large distances, the field lines are very similar
1
4316-4319
FIGURE 5 2 The field lines of (a) a bar magnet, (b) a current-carrying finite solenoid and (c) electric dipole At large distances, the field lines are very similar The curves labelled i and ii are closed Gaussian surfaces
1
4317-4320
2 The field lines of (a) a bar magnet, (b) a current-carrying finite solenoid and (c) electric dipole At large distances, the field lines are very similar The curves labelled i and ii are closed Gaussian surfaces Rationalised 2023-24 139 Magnetism and Matter The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid
1
4318-4321
At large distances, the field lines are very similar The curves labelled i and ii are closed Gaussian surfaces Rationalised 2023-24 139 Magnetism and Matter The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid Cutting a bar magnet in half is like cutting a solenoid
1
4319-4322
The curves labelled i and ii are closed Gaussian surfaces Rationalised 2023-24 139 Magnetism and Matter The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid Cutting a bar magnet in half is like cutting a solenoid We get two smaller solenoids with weaker magnetic properties
1
4320-4323
Rationalised 2023-24 139 Magnetism and Matter The resemblance of magnetic field lines for a bar magnet and a solenoid suggest that a bar magnet may be thought of as a large number of circulating currents in analogy with a solenoid Cutting a bar magnet in half is like cutting a solenoid We get two smaller solenoids with weaker magnetic properties The field lines remain continuous, emerging from one face of the solenoid and entering into the other face
1
4321-4324
Cutting a bar magnet in half is like cutting a solenoid We get two smaller solenoids with weaker magnetic properties The field lines remain continuous, emerging from one face of the solenoid and entering into the other face One can test this analogy by moving a small compass needle in the neighbourhood of a bar magnet and a current-carrying finite solenoid and noting that the deflections of the needle are similar in both cases
1
4322-4325
We get two smaller solenoids with weaker magnetic properties The field lines remain continuous, emerging from one face of the solenoid and entering into the other face One can test this analogy by moving a small compass needle in the neighbourhood of a bar magnet and a current-carrying finite solenoid and noting that the deflections of the needle are similar in both cases To make this analogy more firm we calculate the axial field of a finite solenoid depicted in Fig
1
4323-4326
The field lines remain continuous, emerging from one face of the solenoid and entering into the other face One can test this analogy by moving a small compass needle in the neighbourhood of a bar magnet and a current-carrying finite solenoid and noting that the deflections of the needle are similar in both cases To make this analogy more firm we calculate the axial field of a finite solenoid depicted in Fig 5
1
4324-4327
One can test this analogy by moving a small compass needle in the neighbourhood of a bar magnet and a current-carrying finite solenoid and noting that the deflections of the needle are similar in both cases To make this analogy more firm we calculate the axial field of a finite solenoid depicted in Fig 5 3 (a)
1
4325-4328
To make this analogy more firm we calculate the axial field of a finite solenoid depicted in Fig 5 3 (a) We shall demonstrate that at large distances this axial field resembles that of a bar magnet
1
4326-4329
5 3 (a) We shall demonstrate that at large distances this axial field resembles that of a bar magnet 0 3 2 4 m B r µ π = (5
1
4327-4330
3 (a) We shall demonstrate that at large distances this axial field resembles that of a bar magnet 0 3 2 4 m B r µ π = (5 1) This is also the far axial magnetic field of a bar magnet which one may obtain experimentally
1
4328-4331
We shall demonstrate that at large distances this axial field resembles that of a bar magnet 0 3 2 4 m B r µ π = (5 1) This is also the far axial magnetic field of a bar magnet which one may obtain experimentally Thus, a bar magnet and a solenoid produce similar magnetic fields
1
4329-4332
0 3 2 4 m B r µ π = (5 1) This is also the far axial magnetic field of a bar magnet which one may obtain experimentally Thus, a bar magnet and a solenoid produce similar magnetic fields The magnetic moment of a bar magnet is thus equal to the magnetic moment of an equivalent solenoid that produces the same magnetic field
1
4330-4333
1) This is also the far axial magnetic field of a bar magnet which one may obtain experimentally Thus, a bar magnet and a solenoid produce similar magnetic fields The magnetic moment of a bar magnet is thus equal to the magnetic moment of an equivalent solenoid that produces the same magnetic field 5
1
4331-4334
Thus, a bar magnet and a solenoid produce similar magnetic fields The magnetic moment of a bar magnet is thus equal to the magnetic moment of an equivalent solenoid that produces the same magnetic field 5 2
1
4332-4335
The magnetic moment of a bar magnet is thus equal to the magnetic moment of an equivalent solenoid that produces the same magnetic field 5 2 3 The dipole in a uniform magnetic field Let’s place a small compass needle of known magnetic moment m and allowing it to oscillate in the magnetic field
1
4333-4336
5 2 3 The dipole in a uniform magnetic field Let’s place a small compass needle of known magnetic moment m and allowing it to oscillate in the magnetic field This arrangement is shown in Fig
1
4334-4337
2 3 The dipole in a uniform magnetic field Let’s place a small compass needle of known magnetic moment m and allowing it to oscillate in the magnetic field This arrangement is shown in Fig 5
1
4335-4338
3 The dipole in a uniform magnetic field Let’s place a small compass needle of known magnetic moment m and allowing it to oscillate in the magnetic field This arrangement is shown in Fig 5 3(b)
1
4336-4339
This arrangement is shown in Fig 5 3(b) The torque on the needle is [see Eq
1
4337-4340
5 3(b) The torque on the needle is [see Eq (4
1
4338-4341
3(b) The torque on the needle is [see Eq (4 23)], ttttt = m × B (5
1
4339-4342
The torque on the needle is [see Eq (4 23)], ttttt = m × B (5 2) In magnitude t = mB sinq Here ttttt is restoring torque and q is the angle between m and B
1
4340-4343
(4 23)], ttttt = m × B (5 2) In magnitude t = mB sinq Here ttttt is restoring torque and q is the angle between m and B An expression for magnetic potential energy can also be obtained on lines similar to electrostatic potential energy
1
4341-4344
23)], ttttt = m × B (5 2) In magnitude t = mB sinq Here ttttt is restoring torque and q is the angle between m and B An expression for magnetic potential energy can also be obtained on lines similar to electrostatic potential energy The magnetic potential energy Um is given by U m = ∫τ θd θ ( ) = = − ∫mB d mB sin cos θ θ θ = –m
1
4342-4345
2) In magnitude t = mB sinq Here ttttt is restoring torque and q is the angle between m and B An expression for magnetic potential energy can also be obtained on lines similar to electrostatic potential energy The magnetic potential energy Um is given by U m = ∫τ θd θ ( ) = = − ∫mB d mB sin cos θ θ θ = –m B (5
1
4343-4346
An expression for magnetic potential energy can also be obtained on lines similar to electrostatic potential energy The magnetic potential energy Um is given by U m = ∫τ θd θ ( ) = = − ∫mB d mB sin cos θ θ θ = –m B (5 3) We have emphasised in Chapter 2 that the zero of potential energy can be fixed at one’s convenience
1
4344-4347
The magnetic potential energy Um is given by U m = ∫τ θd θ ( ) = = − ∫mB d mB sin cos θ θ θ = –m B (5 3) We have emphasised in Chapter 2 that the zero of potential energy can be fixed at one’s convenience Taking the constant of integration to be zero means fixing the zero of potential energy at q = 90°, i
1
4345-4348
B (5 3) We have emphasised in Chapter 2 that the zero of potential energy can be fixed at one’s convenience Taking the constant of integration to be zero means fixing the zero of potential energy at q = 90°, i e
1
4346-4349
3) We have emphasised in Chapter 2 that the zero of potential energy can be fixed at one’s convenience Taking the constant of integration to be zero means fixing the zero of potential energy at q = 90°, i e , when the needle is perpendicular to the field
1
4347-4350
Taking the constant of integration to be zero means fixing the zero of potential energy at q = 90°, i e , when the needle is perpendicular to the field Equation (5
1
4348-4351
e , when the needle is perpendicular to the field Equation (5 6) shows that potential energy is minimum (= –mB) at q = 0° (most stable position) and maximum (= +mB) at q = 180° (most unstable position)
1
4349-4352
, when the needle is perpendicular to the field Equation (5 6) shows that potential energy is minimum (= –mB) at q = 0° (most stable position) and maximum (= +mB) at q = 180° (most unstable position) Example 5
1
4350-4353
Equation (5 6) shows that potential energy is minimum (= –mB) at q = 0° (most stable position) and maximum (= +mB) at q = 180° (most unstable position) Example 5 1 (a) What happens if a bar magnet is cut into two pieces: (i) transverse to its length, (ii) along its length
1
4351-4354
6) shows that potential energy is minimum (= –mB) at q = 0° (most stable position) and maximum (= +mB) at q = 180° (most unstable position) Example 5 1 (a) What happens if a bar magnet is cut into two pieces: (i) transverse to its length, (ii) along its length (b) A magnetised needle in a uniform magnetic field experiences a torque but no net force
1
4352-4355
Example 5 1 (a) What happens if a bar magnet is cut into two pieces: (i) transverse to its length, (ii) along its length (b) A magnetised needle in a uniform magnetic field experiences a torque but no net force An iron nail near a bar magnet, however, experiences a force of attraction in addition to a torque
1
4353-4356
1 (a) What happens if a bar magnet is cut into two pieces: (i) transverse to its length, (ii) along its length (b) A magnetised needle in a uniform magnetic field experiences a torque but no net force An iron nail near a bar magnet, however, experiences a force of attraction in addition to a torque Why
1
4354-4357
(b) A magnetised needle in a uniform magnetic field experiences a torque but no net force An iron nail near a bar magnet, however, experiences a force of attraction in addition to a torque Why EXAMPLE 5
1
4355-4358
An iron nail near a bar magnet, however, experiences a force of attraction in addition to a torque Why EXAMPLE 5 1 Rationalised 2023-24 Physics 140 EXAMPLE 5
1
4356-4359
Why EXAMPLE 5 1 Rationalised 2023-24 Physics 140 EXAMPLE 5 1 (c) Must every magnetic configuration have a north pole and a south pole
1
4357-4360
EXAMPLE 5 1 Rationalised 2023-24 Physics 140 EXAMPLE 5 1 (c) Must every magnetic configuration have a north pole and a south pole What about the field due to a toroid
1
4358-4361
1 Rationalised 2023-24 Physics 140 EXAMPLE 5 1 (c) Must every magnetic configuration have a north pole and a south pole What about the field due to a toroid (d) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised
1
4359-4362
1 (c) Must every magnetic configuration have a north pole and a south pole What about the field due to a toroid (d) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised (We do not know which one
1
4360-4363
What about the field due to a toroid (d) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised (We do not know which one ) How would one ascertain whether or not both are magnetised
1
4361-4364
(d) Two identical looking iron bars A and B are given, one of which is definitely known to be magnetised (We do not know which one ) How would one ascertain whether or not both are magnetised If only one is magnetised, how does one ascertain which one
1
4362-4365
(We do not know which one ) How would one ascertain whether or not both are magnetised If only one is magnetised, how does one ascertain which one [Use nothing else but the bars A and B
1
4363-4366
) How would one ascertain whether or not both are magnetised If only one is magnetised, how does one ascertain which one [Use nothing else but the bars A and B ] Solution (a) In either case, one gets two magnets, each with a north and south pole
1
4364-4367
If only one is magnetised, how does one ascertain which one [Use nothing else but the bars A and B ] Solution (a) In either case, one gets two magnets, each with a north and south pole (b) No force if the field is uniform
1
4365-4368
[Use nothing else but the bars A and B ] Solution (a) In either case, one gets two magnets, each with a north and south pole (b) No force if the field is uniform The iron nail experiences a non- uniform field due to the bar magnet
1
4366-4369
] Solution (a) In either case, one gets two magnets, each with a north and south pole (b) No force if the field is uniform The iron nail experiences a non- uniform field due to the bar magnet There is induced magnetic moment in the nail, therefore, it experiences both force and torque
1
4367-4370
(b) No force if the field is uniform The iron nail experiences a non- uniform field due to the bar magnet There is induced magnetic moment in the nail, therefore, it experiences both force and torque The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole
1
4368-4371
The iron nail experiences a non- uniform field due to the bar magnet There is induced magnetic moment in the nail, therefore, it experiences both force and torque The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole (c) Not necessarily
1
4369-4372
There is induced magnetic moment in the nail, therefore, it experiences both force and torque The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole (c) Not necessarily True only if the source of the field has a net non-zero magnetic moment
1
4370-4373
The net force is attractive because the induced south pole (say) in the nail is closer to the north pole of magnet than induced north pole (c) Not necessarily True only if the source of the field has a net non-zero magnetic moment This is not so for a toroid or even for a straight infinite conductor
1
4371-4374
(c) Not necessarily True only if the source of the field has a net non-zero magnetic moment This is not so for a toroid or even for a straight infinite conductor (d) Try to bring different ends of the bars closer
1
4372-4375
True only if the source of the field has a net non-zero magnetic moment This is not so for a toroid or even for a straight infinite conductor (d) Try to bring different ends of the bars closer A repulsive force in some situation establishes that both are magnetised
1
4373-4376
This is not so for a toroid or even for a straight infinite conductor (d) Try to bring different ends of the bars closer A repulsive force in some situation establishes that both are magnetised If it is always attractive, then one of them is not magnetised
1
4374-4377
(d) Try to bring different ends of the bars closer A repulsive force in some situation establishes that both are magnetised If it is always attractive, then one of them is not magnetised In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region
1
4375-4378
A repulsive force in some situation establishes that both are magnetised If it is always attractive, then one of them is not magnetised In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region This fact may be used to determine whether A or B is the magnet
1
4376-4379
If it is always attractive, then one of them is not magnetised In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region This fact may be used to determine whether A or B is the magnet In this case, to see which one of the two bars is a magnet, pick up one, (say, A) and lower one of its ends; first on one of the ends of the other (say, B), and then on the middle of B
1
4377-4380
In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region This fact may be used to determine whether A or B is the magnet In this case, to see which one of the two bars is a magnet, pick up one, (say, A) and lower one of its ends; first on one of the ends of the other (say, B), and then on the middle of B If you notice that in the middle of B, A experiences no force, then B is magnetised
1
4378-4381
This fact may be used to determine whether A or B is the magnet In this case, to see which one of the two bars is a magnet, pick up one, (say, A) and lower one of its ends; first on one of the ends of the other (say, B), and then on the middle of B If you notice that in the middle of B, A experiences no force, then B is magnetised If you do not notice any change from the end to the middle of B, then A is magnetised
1
4379-4382
In this case, to see which one of the two bars is a magnet, pick up one, (say, A) and lower one of its ends; first on one of the ends of the other (say, B), and then on the middle of B If you notice that in the middle of B, A experiences no force, then B is magnetised If you do not notice any change from the end to the middle of B, then A is magnetised 5
1
4380-4383
If you notice that in the middle of B, A experiences no force, then B is magnetised If you do not notice any change from the end to the middle of B, then A is magnetised 5 2
1
4381-4384
If you do not notice any change from the end to the middle of B, then A is magnetised 5 2 4 The electrostatic analog Comparison of Eqs
1
4382-4385
5 2 4 The electrostatic analog Comparison of Eqs (5
1
4383-4386
2 4 The electrostatic analog Comparison of Eqs (5 2), (5
1
4384-4387
4 The electrostatic analog Comparison of Eqs (5 2), (5 3) and (5
1
4385-4388
(5 2), (5 3) and (5 6) with the corresponding equations for electric dipole (Chapter 1), suggests that magnetic field at large distances due to a bar magnet of magnetic moment m can be obtained from the equation for electric field due to an electric dipole of dipole moment p, by making the following replacements: E→ B , p m → , 0 0 1 4 4 µ ε → π π In particular, we can write down the equatorial field (BE) of a bar magnet at a distance r, for r >> l, where l is the size of the magnet: 0 3 4 E r = −µ π m B (5
1
4386-4389
2), (5 3) and (5 6) with the corresponding equations for electric dipole (Chapter 1), suggests that magnetic field at large distances due to a bar magnet of magnetic moment m can be obtained from the equation for electric field due to an electric dipole of dipole moment p, by making the following replacements: E→ B , p m → , 0 0 1 4 4 µ ε → π π In particular, we can write down the equatorial field (BE) of a bar magnet at a distance r, for r >> l, where l is the size of the magnet: 0 3 4 E r = −µ π m B (5 4) Likewise, the axial field (BA) of a bar magnet for r >> l is: 0 3 2 4 A r =µ π m B (5
1
4387-4390
3) and (5 6) with the corresponding equations for electric dipole (Chapter 1), suggests that magnetic field at large distances due to a bar magnet of magnetic moment m can be obtained from the equation for electric field due to an electric dipole of dipole moment p, by making the following replacements: E→ B , p m → , 0 0 1 4 4 µ ε → π π In particular, we can write down the equatorial field (BE) of a bar magnet at a distance r, for r >> l, where l is the size of the magnet: 0 3 4 E r = −µ π m B (5 4) Likewise, the axial field (BA) of a bar magnet for r >> l is: 0 3 2 4 A r =µ π m B (5 5) Rationalised 2023-24 141 Magnetism and Matter Equation (5
1
4388-4391
6) with the corresponding equations for electric dipole (Chapter 1), suggests that magnetic field at large distances due to a bar magnet of magnetic moment m can be obtained from the equation for electric field due to an electric dipole of dipole moment p, by making the following replacements: E→ B , p m → , 0 0 1 4 4 µ ε → π π In particular, we can write down the equatorial field (BE) of a bar magnet at a distance r, for r >> l, where l is the size of the magnet: 0 3 4 E r = −µ π m B (5 4) Likewise, the axial field (BA) of a bar magnet for r >> l is: 0 3 2 4 A r =µ π m B (5 5) Rationalised 2023-24 141 Magnetism and Matter Equation (5 8) is just Eq
1
4389-4392
4) Likewise, the axial field (BA) of a bar magnet for r >> l is: 0 3 2 4 A r =µ π m B (5 5) Rationalised 2023-24 141 Magnetism and Matter Equation (5 8) is just Eq (5