Why is Force perpendicular to the velocity and magnetic field ?

I know it's a cross product whose magnitude of force is given by

𝐹⃗=𝑞 𝑢⃗×𝐵⃗

but why is that ? I mean when an electrically charged particle with initially velocity perpendicular to electric field moves in direction of field lines why isn't it moving in direction of magnetic field ?

When i am searching google for that answer [1]:


it's giving me some answer which is not suitable for a high school student ?

  • $\begingroup$ It is law f=qvxb ,and universally valid ,actually there is no reason to define ,why the things happen like this. $\endgroup$
    – Jack Rod
    Aug 28, 2019 at 7:50

1 Answer 1


This in some sense has got to do with the fact that nature does not have magnetic charges. Only dipoles. These dipoles can be thought of as an arrow pointing perpendicular to the plane that the charge is rotating in.

The action of the magnetic field is to get this magnetic dipole to align with it. In order for the dipole to align with the field, the charge has to rotate perpendicular to the field. That’s why the force acts in the perpendicular direction.

Now if the charge isn’t initially rotating, then the magnetic field will make it rotate so as to have a dipole pointing along the field. And this can only happen if the force is perpendicular to the velocity and field both.


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