# Electromagnetism problems with answers

Recent questions in Electromagnetism

### Magnetic force on open circuit?Let's say we have a straight horizontal wire and we let it drop inside a magnetic field which will be parallel to the ground(coming out of the screen). Charges inside the wire feel a force due to their movement inside the magnetic field .Let's say the field is coming out of the screen. Positive charges gather on the left and negative on the right. If we had a loop I would have no trouble with this but during the charges' movement do we consider that we have a current? Therefore leading to a magnetic force opposing the bar's drop or not?

Ashley Fritz 2022-05-15 Answered

### Direction of magnetic forceDoes magnetic force act along the line joining the centres like gravitational and electric forces do?Are the directions of magnetic field and magnetic lines of force the same? I have read that the direction of the field is tangential to the direction of the line of force.

Alisa Durham 2022-05-15 Answered

### Is magnetic force pseudo?Magnetic force exist only if charge is moving, so it must be pseudo. Imagine, a positively charged man who has the same speed as electron (charge). So, he doesn't feel any magnetic force as charge is at rest with respect to him. Therefore, he only experience electric force.However a man who is at rest or has different speed than electron feels a magnetic forceTherefore magnetic force must be pseudo. Pls answer me

Jayden Mckay 2022-05-14 Answered

### Gauss's Law of Magnetism shows us that the divergence of Magnetic field is 0, $▽\cdot \stackrel{\to }{B}=0$Then how do you derive that statement by showing the divergence of a magnetic field upon an axis of a current carrying coil where radius is much smaller that distance so that we can use,${B}_{z}=\frac{{\mu }_{o}I}{2{z}^{3}}\stackrel{^}{z}$$\therefore$$▽\cdot B\equiv \frac{\mathrm{\partial }}{\mathrm{\partial }z}\cdot \frac{{u}_{o}I}{2{z}^{3}}\stackrel{^}{z}\ne 0$This doesn't equal zero? What am I missing?

Brooklynn Hubbard 2022-05-13 Answered

### Why are the electric force and magnetic force classified as electromagnetism?I confuse the four kinds of fundamental interactions, so I think the electric force and magnetic force should not be classified as a big class called electromagnetism.Here is my evidence:1.The Gauss law of electric force is related to the surface integration but the Ampere's law corresponds with path integration.2.The electric field can be caused by a single static charge while the magnetic force is caused by a moving charge or two moving infinitesimal current.3.The electric field line is never closed, but the magnetic field line (except those to infinity) is a closed curve.

Blaine Stein 2022-05-13 Answered

### Magnetic force between moving chargesGiven two infinite parallel charged rods with equal charge density $\lambda$. They are moving with same constant velocity $\stackrel{\to }{v}$ parallel to the rods. Find the speed $v$ for which the magnetic attraction is equal to the electrostatic repulsion.Well, I know how to solve this problem: we first find out the magnetic field created by one rod on the other using Biot's and Savart's law, then we use the definition of $\stackrel{\to }{B}$ ( $d\stackrel{\to }{F}=\stackrel{\to }{v}dq×\stackrel{\to }{B}$ ) to find the magnetic force, then equate magnetic and electrostatic forces to find $v$, which will be greater than or equal to $c$, thus conclude it is impossible for the forces to be equal.However, one can argue as the following:We all know that "same laws of physics apply in all inertial frames". With a constant velocity $\stackrel{\to }{v}$,the rest frame of the rods is an inertial frame. Therefore, if Biot-Savart law applies in our frame, it has to apply in the rest frame. If so, none of the rods will feel a magnetic field from the other one because their relative speed is zero, and there will be no magnetic force between the rods.I've seen this question several times before in references, exams, exercise sheets,and in many different forms (parallel planes, beam of electrons ...),but no one ever used this argument.What is the problem in it ? Is it something related to Maxwell's equations or special relativity ? Or what else ?I know a similar question was asked before, but the answers weren't satisfying. Please provide your answers with necessary mathematics.

Bernard Mora 2022-05-10 Answered

### In Maxwell's equations, I understand intuitively how: $\oint B\cdot da=0$ (because there are no monopoles and so equal number of field lines going in and coming out of the surface).And then using the divergence theorem:${\int }_{V}\left(\mathrm{\nabla }\cdot B\right)d\tau ={\oint }_{S}B\cdot da$Then ${\int }_{V}\left(\mathrm{\nabla }\cdot B\right)d\tau$ must be = 0.But then I'm not sure why I can say: $\mathrm{\nabla }\cdot B=0$ and forget about the integral.Does it just mean that $\mathrm{\nabla }\cdot B$ must be zero everywhere?

Damion Hardin 2022-05-10 Answered

### Electric Force is to Magnetic Force as Gravitational Force is to ...?One can no nothing about the magnetic force and yet arrive at it by taking the relativistic effects of a current and a moving charge system into account. I ask whether there exists such an inherent force in case of gravity.\

Yasmine Larson 2022-05-10 Answered

### Magnetic force and workIf the magnetic force does no work on a particle with electric charge, then: How can you influence the motion of the particle? Is there perhaps another example of the work force but do not have a significant effect on the motion of the particle?

Lexi Chandler 2022-05-10 Answered