A radially pulsating charged sphere creates which of these effects?

[LCSphysicist]

Homework Statement

A radially pulsating charged sphere
(a) emits electromagnetic radiation
(b) creates a static magnetic field
(c) can set a nearby electrified particle into motion.

Relevant Equations

.

I know that (a) is right, and (b) is wrong. The problem is with (c)... It seems correct to me! I can't see how this is not true. The electric charge o the sphere by itself will create an electric field, which will move the particle.

 

[Orodruin]

Homework Statement:: A radially pulsating charged sphere
(a) emits electromagnetic radiation
(b) creates a static magnetic field
(c) can set a nearby electrified particle into motion.
Relevant Equations:: .

I know that (a) is right, and (b) is wrong. The problem is with (c)... It seems correct to me! I can't see how this is not true. The electric charge o the sphere by itself will create an electric field, which will move the particle.

What are your arguments?

 

[LCSphysicist]

What are your arguments?

"The electric charge of the sphere by itself will create an electric field, which will move the particle." is my argument.

 

[Orodruin]

"The electric charge of the sphere by itself will create an electric field, which will move the particle." is my argument.

I meant for all of the problems.

 

[LCSphysicist]

I meant for all of the problems.

(a) is correct. It emit radiation, obviously: Since the electric field configuration outside the sphere need to be oscillating, the information arriving at this point comes from the radiation that the oscillation of the sphere produces.
Now, i know there is a physical meaning for radiation, which is the term that didn't goes to zero at r infinity. If this is what the question is asking, that is, if this term is present on the potential, i can't say.

(b) This makes no sense, to create a static configuration of magnetic field, i think, we should have a constant current, or a uniform variating electric field ($\partial E / \partial t = c_{1} \neq 0$), not the case here.

(c) Should be right also. Unless, i can see in my head but not put on math, they are talking about the avarage motion of a particle. What i mean is that, the only system i can see that makes sense to say that the particle does not move, is the one in which the electric field attract the particle, the magnetic field generated by it curves it path so that it returns at the same position after a period, and so tecnically it didn't move. That i can't prove.

 

[Orodruin]

(a) is correct. It emit radiation, obviously: Since the electric field configuration outside the sphere need to be oscillating, the information arriving at this point comes from the radiation that the oscillation of the sphere produces.
Now, i know there is a physical meaning for radiation, which is the term that didn't goes to zero at r infinity. If this is what the question is asking, that is, if this term is present on the potential, i can't say.

Here is a hint: there is no electromagnetic monopole radiation.

 

[LCSphysicist]

Here is a hint: there is no electromagnetic monopole radiation.

I can think about it late, but thank you. By now, i would like to understand how can "c" be wrong.

 

[hutchphd]

Why do you think it wrong ?

 

[LCSphysicist]

Why do you think it wrong ?

OOp, right in time XD.
Because the answer provided is only a.

 

[hutchphd]

Where is this from?

 

[berkeman]

OOp, right in time XD.
Because the answer provided is only a.

Here is a hint: there is no electromagnetic monopole radiation.

I don't know it it will help you @LCSphysicist , but think about how an antenna works. You drive a voltage differentially between the two antenna elements to create a differential voltage and current, and that's what creates the EM field that propagates away from the antenna. If you drive the two antenna elements with the same common-mode current, there is no differential current, so no launching of the EM waveform.

 

[haruspex]

Since the electric field configuration outside the sphere need to be oscillating

What is the field outside a uniformly charged spherical shell of radius r?

 

[Orodruin]

OOp, right in time XD.
Because the answer provided is only a.

Well, that is wrong, so …