Charged particle in a magnetic field

[cherioslover]

Just doing some homework with magnetic fields and was just wondering, why is a charged particle affected by a magnetic field only when its in motion? Physics teacher didn't know so, just wondering if any of you do.

 

[ShayanJ]

Well,as I know,there is no explanation in classical physics.
But in Special Relativity,magnetic fields become emergent fields.They become an effect of the motion of the reference frame in regions that an electric field is present and that explains it.
And about QED,the quantum theory of Electromagnetism,my guess is that because it agrees with Special Relativity,it uses the same explanation.

 

[Vanadium 50]

It's convention.

Particles are affected by the electromagnetic interaction. We define the electric piece as the velocity-independent part, and the magnetic piece as the velocity-dependent part. We could have factorized this differently or not at all. The choice we made is convenient and historical, so we keep using it.

 

[ShayanJ]

It's convention.

Particles are affected by the electromagnetic interaction. We define the electric piece as the velocity-independent part, and the magnetic piece as the velocity-dependent part. We could have factorized this differently or not at all. The choice we made is convenient and historical, so we keep using it.

Its not completely conventional!
Imagine we haven't made the factorization,then one would ask why the Elemgetic force(!) depends on velocity!
In fact no factorization can eliminate the velocity-dependence and so the question can always be asked,only the field which is mentioned in the question would be different!

 

[sardar]

This is a great question! The reason why a charged particle is affected by a magnetic field only when it is in motion is because a magnetic field exerts a force on a moving charged particle. This force is known as the Lorentz force and it is given by the equation F = qv x B, where q is the charge of the particle, v is its velocity, and B is the magnetic field. This force acts perpendicular to both the velocity of the particle and the direction of the magnetic field.

When a charged particle is at rest, there is no velocity component in the equation, so the force would be zero. However, when the particle is in motion, the velocity component is non-zero and the particle experiences a force that causes it to move in a circular path perpendicular to the direction of the magnetic field. This is known as circular motion and is a result of the Lorentz force.

In summary, a charged particle is affected by a magnetic field only when it is in motion because the magnetic field exerts a force on the particle, causing it to move in a circular path. This phenomenon is crucial in many applications, such as in particle accelerators and magnetic resonance imaging (MRI) machines. I hope this helps clarify your question!