Question on magnetism: Circular motion of charged particle in a Magnetic Field

[PeroK]

here's the deal, if you can prove the answer is B using high school physics then I will send the examiners report

The answer is B whether you use the Lorentz force law or the Fleming rule.

 

[physicals]

With learning must come humility and acceptance as well, i am sorry to have lied about the examiner report, after some proper thinking i have concluded that the right answer is B, using my earlier reasoning for the centripetal force and magnetic force, the magnetic field indeed goes into the page. But were all this confusion really came from is this (Flemings right hand rule here is Lorentz force law) i dont understand the difference between the two:

 

[vela]

For the left-hand rule, the current is the input and force is the output. That is, it tells you how to calculate the direction of $\vec F = I \vec l \times \vec B$ given a current moving in the direction of $\vec l$ in a field $\vec B$. For the right-hand rule, the roles are switched. The motion (misleadingly called force in the diagram) is the input, and the current is the output. It tells you how the calculate the direction of $\vec F = q \vec v \times \vec B$, the force exerted on a charge moving with velocity $\vec v$ in a magnetic field $\vec B$. The force on the charge may cause the charge to move, producing a current.

Both rules are actually the Lorentz force law, but you have to identify the quantities in the problem correctly.

 

[physicals]

so the magnetic field pushes the particle instead of pull? then how is there circular motion?

 

[PeroK]

so the magnetic field pushes the particle instead of pull? then how is there circular motion?

A force is a force. A force of constant magnitude that is always perpendicular to the velocity results in circular motion.