Finding Magnetic Field from Electric Field: A Classical Physics Problem

In summary, the conversation discusses finding an expression for the magnetic field associated with a given electric field in classical physics. The usual method of finding the propagation direction and taking the cross product with the direction of E does not work in this case due to the standing wave nature of the given equation. Instead, the speaker suggests using the curl of E and integrating with respect to time to obtain the equation for B. The other person in the conversation agrees that this approach seems correct.
  • #1
OhNoYaDidn't
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Hey guys, i just came across this on my classical physics course.
So, I'm given that: [tex]E(z, t) = {E_{0}}sin(wt)sin(kz)\widehat{x}[/tex], and I'm supposed to find an expression for the associated magnetic field B.

Usually, i just find the propagation direction, and do it's cross product with the direction of E, and then write it as [tex]\overrightarrow{B}(r,t)=\frac{1}{c}\widehat{k}\times \overrightarrow{E} [/tex]but in this case, it doesn't seem to be as straightforward.

I thought of using [tex]\triangledown \times \overrightarrow{E} = -\frac{\partial \overrightarrow{B}}{\partial t}[/tex], finding the curl of E, and then integrate with respect to time, this would give me:

[tex] B(z, t) = \frac{k}{w}{E_{0}}cos(kz)cos(wt)\widehat{y} [/tex]

Is this right?
Thank you.
 
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  • #2
Yes seems right to me. It is just that the equation that is given for E, represents a standing wave, so the propagation vector cannot be defined (standing waves do not propagate).
 
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1. How do you find the magnetic field from an electric field?

In classical physics, the magnetic field can be found by using the following equation: B = μ0 * (1/c^2) * (E x v), where B is the magnetic field, μ0 is the permeability of free space, c is the speed of light, E is the electric field, and v is the velocity of the charged particle. This equation is known as the Lorentz force law and it shows that the magnetic field is directly proportional to both the electric field and the velocity of the charged particle.

2. What is the relationship between electric and magnetic fields?

Electric and magnetic fields are two fundamental components of the electromagnetic force. They are closely related and can be thought of as two different aspects of the same force. A changing electric field can produce a magnetic field, and a changing magnetic field can produce an electric field. This is known as electromagnetic induction and is the basis for many technologies, such as generators and transformers.

3. Can you calculate the magnetic field without knowing the velocity of the charged particle?

No, the velocity of the charged particle is a crucial component in calculating the magnetic field using the Lorentz force law. Without knowing the velocity, it is not possible to accurately determine the strength and direction of the magnetic field. However, it is possible to estimate the velocity by measuring the electric and magnetic fields at different points and using mathematical techniques such as integration or differentiation.

4. How does the strength of the magnetic field change with distance from the charged particle?

The strength of the magnetic field decreases as the distance from the charged particle increases. This is because the magnetic field is inversely proportional to the square of the distance from the source. In other words, the farther away you are from the charged particle, the weaker the magnetic field will be. This relationship is similar to the inverse-square law for gravitational force.

5. Can the magnetic field from an electric field be shielded or blocked?

Yes, the magnetic field from an electric field can be shielded or blocked in a similar way to how electric fields can be shielded or blocked. This can be achieved by using materials with high magnetic permeability, which can redirect or absorb the magnetic field. Additionally, the orientation and arrangement of these materials can also affect the effectiveness of the shielding or blocking. This principle is used in devices such as magnetic shields and MRI machines.

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