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Write out Maxwell's equations as they would appear if we had magnetic charge and magnetic currents as well as electric charge and electric currents. Invent any new symbols you need and define carefully what they stand for. Be particularly careful about \(+\) and \(-\) signs.

Short Answer

Expert verified
By introducing new symbols \( q_m \) for magnetic charges (mono-poles) and \( J_m \) for magnetic currents and incorporating them into the traditional Maxwell's equations, these equations are adjusted. Therefore, the four modified Maxwell's equations now include both electric and magnetic charges and currents, and they are as follows: \(\nabla\cdot B = 渭_0 q_m\), \(\nabla\cdot E = \frac{蟻 - 渭_0 q_m}{\varepsilon_0}\), \(\nabla\times B = 渭_0J+渭_0 J_m +渭_0\varepsilon_0\frac{\partial E}{\partial t}\), \(\nabla\times E = -\frac{\partial B}{\partial t}\ - 渭_0 J_m\).

Step by step solution

01

Understand Maxwell's Traditional Equations

We first need to recall Maxwell's traditional equations. These equations are given by: \n\n Gauss Law: \(\nabla\cdot E = \frac{蟻}{\varepsilon_0}\)\n\n Gauss's Law for Magnetism: \(\nabla\cdot B = 0\)\n\n Faraday's Law of Induction: \(\nabla\times E = -\frac{\partial B}{\partial t}\)\n\n Ampere's Law with Maxwell's Addition: \(\nabla\times B = 渭_0J+渭_0\varepsilon_0\frac{\partial E}{\partial t}\)
02

Add Magnetic Charges and Currents

To include magnetic charges (described as \(q_m\)), and magnetic current with a density (\(J_m\)), it is needed to integrate a magnetic scalar field into the equations. Let's denote this scalar field as \(\vec{M}\), representing magnetic charges. The new symbols \(q_m\) represent magnetic charges and \(J_m\) represent magnetic currents.
03

Revise Maxwell's Equations

Now, alter Maxwell's equations to include these new magnetic charges (\(q_m\)) and currents (\(J_m\)). The equations change as follows: \n\n Magnetic Gauss Law: \(\nabla\cdot B = 渭_0 q_m\)\n\n Electric Gauss's Law : \(\nabla\cdot E = \frac{蟻 - 渭_0 q_m}{\varepsilon_0}\)\n\n The Ampere's Law with Maxwell's Addition becomes: \(\nabla\times B = 渭_0J+渭_0 J_m +渭_0\varepsilon_0\frac{\partial E}{\partial t}\)\n\n The Faraday's Law of Induction changes to: \(\nabla\times E = -\frac{\partial B}{\partial t} - 渭_0 J_m\)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Magnetic Gauss Law
Imagine a universe with magnetic charges, similar to electric charges, and how that would affect one of Maxwell's equations known as the Magnetic Gauss Law. Traditionally, this law states that the net magnetic flux out of any closed surface is zero, mathematically expressed as \(abla\bullet B = 0\). This implies that magnetic poles always exist as dipoles, with no isolated north or south poles, commonly referred to as 'magnetic monopoles'.

However, if magnetic charges did exist, which we'll represent with \(q_m\), the law would be modified to include these charges, and would be written as \(abla\bullet B = \text{渭}_0 q_m\). Here, \(B\) is the magnetic field, \(q_m\) represents the hypothetical magnetic charge, and \(\text{渭}_0\) is the permeability of free space. This equation would now imply that magnetic charges can be sources or sinks of magnetic fields, just like electric charges are for electric fields.
Electric Gauss's Law
In the realm of electromagnetism, the Electric Gauss's Law is a fundamental principle that relates the electric charges within a given volume to the electric field emanating from that volume. The standard law is given by \(abla\bullet E = \frac{蟻}{\text{蔚}_0}\), where \(E\) is the electric field, \(蟻\) is the electric charge density, and \(\text{蔚}_0\) stands for the permittivity of free space.

If magnetic charges, denoted as \(q_m\), were also present, we would need to consider their influence on the electric field. Therefore, the modified Electric Gauss's Law would take the form \(abla\bullet E = \frac{蟻 - \text{渭}_0 q_m}{\text{蔚}_0}\). The addition of \(- \text{渭}_0 q_m\) in the numerator reflects the potential impact of magnetic charges on the electric field, combining to show that both electric and magnetic charges have a role in determining the behavior of the electric field around them.
Ampere's Law with Maxwell's Addition
Ampere's Law with Maxwell's Addition is one of the cornerstones of classical electromagnetism, connecting the magnetic field around a current-carrying conductor with the electric current itself. Traditionally, this law can be articulated as \(abla\times B = \text{渭}_0J + \text{渭}_0\text{蔚}_0\frac{\text{鈭倉E}{\text{鈭倉t}\), where \(B\) is the magnetic field, \(J\) is the electric current density, and the term \(\text{渭}_0\text{蔚}_0\frac{\text{鈭倉E}{\text{鈭倉t}\) represents Maxwell's addition accounting for the changing electric field's contribution to the magnetic field.

Introducing magnetic currents, \(J_m\), to this scenario requires adapting the equation to accommodate these new sources of magnetism. The equation then evolves into \(abla\times B = \text{渭}_0J + \text{渭}_0J_m + \text{渭}_0\text{蔚}_0\frac{\text{鈭倉E}{\text{鈭倉t}\). This adjusted form asserts that magnetic currents, much like their electric counterparts, create a curling magnetic field, fundamentally altering the interaction between electricity and magnetism.
Faraday's Law of Induction
Faraday's Law of Induction is a basic principle that outlines how a changing magnetic field can induce an electric field. The standard expression for this law is \(abla\times E = -\frac{\text{鈭倉B}{\text{鈭倉t}\), signaling that a time-varying magnetic field \(B\) produces an electric field \(E\), whose curl is proportional to the negative rate of change of the magnetic field.

However, if magnetic currents existed, the equation would be modified to include the effects of these currents on the induced electric field, resulting in \(abla\times E = -\frac{\text{鈭倉B}{\text{鈭倉t} - \text{渭}_0 J_m\). In this updated equation, the term \(- \text{渭}_0 J_m\) represents the additional electric field induced by the magnetic current \(J_m\). Thus, both the change in the magnetic field over time, as well as the presence of magnetic currents, would contribute to the generation of an electric field.

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Most popular questions from this chapter

A sphere of radius \(R\) carries charge \(Q\) distributed uniformly over the surface, with density \(\sigma=Q / 4 \pi R^{2}\). This shell of charge is rotating about an axis of the sphere with angular speed \(\omega\). Find its magnetic moment. (Divide the sphere into narrow bands of rotating charge; find the current to which each band is equivalent, and its dipole moment, and then integrate over all bands.)

A cylindrical solenoid has a single-layer winding of radius \(r_{0}\). It is so long that near one end the field may be taken to be that of a semi-infinite solenoid. Show that the point on the axis of the solenoid where a small paramagnetic sample will experience the greatest force is located a distance \(r_{0} / \sqrt{15}\) in from the end.

In Problem \(11.8\) we found the magnetic field \(\mathbf{B}\) inside a sphere with uniform magnetization \(\mathbf{M}\). The task of this exercise is to rederive that result by making use of the result from Section \(10.9\) for a uniformly polarized sphere, namely \(\mathbf{E}=-\mathbf{P} / 3 \epsilon_{0}\). To do this, consider the following equations that are valid for static fields: $$ \begin{aligned} \nabla \cdot\left(\epsilon_{0} \mathbf{E}+\mathbf{P}\right) &=\rho_{\text {free }}, & \nabla \cdot \mathbf{B} &=0 \\ \nabla \times \mathbf{E} &=0, & \nabla \times\left(\mathbf{B} / \mu_{0}-\mathbf{M}\right) &=\mathbf{J}_{\text {free }} \end{aligned} $$ (The first and last of these are Eqs. (10.62) and (11.67).) If additionally \(\rho_{\text {free }}=0\) and \(\mathbf{J}_{\text {free }}=0\), which is the case for our polarized and magnetized spheres, the right-hand sides of all the equations are zero. Rewrite the two magnetic equations in terms of \(\mathbf{H}\), and then take advantage of the resulting similarity with the electric equations.

A disk with radius \(R\) has uniform surface charge density \(\sigma\) and spins with angular speed \(\omega\). Far away, it looks like a magnetic dipole. What is the magnetic dipole moment?

At the north magnetic pole the earth's magnetic field is vertical and has a strength of \(0.62\) gauss. The earth's field at the surface and further out is approximately that of a central dipole. (a) What is the magnitude of the dipole moment in joules/tesla? (b) Imagine that the source of the field is a current ring on the "equator" of the earth's metallic core, which has a radius of \(3000 \mathrm{~km}\), about half the earth's radius. How large would the current have to be?

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