Question

if the velocity of a charges particle is in the same direction as the applied magnetic field, what is the force experienced by it going to do?
a) slow it down
b) speed it up
c) no force

Explanation:

The magnetic - force on a charged particle is given by $\vec{F}=q\vec{v}\times\vec{B}$, where $\vec{F}$ is the force, $q$ is the charge of the particle, $\vec{v}$ is the velocity vector, and $\vec{B}$ is the magnetic - field vector. The magnitude of the cross - product $|\vec{v}\times\vec{B}| = |\vec{v}||\vec{B}|\sin\theta$, where $\theta$ is the angle between $\vec{v}$ and $\vec{B}$. When $\vec{v}$ and $\vec{B}$ are in the same direction, $\theta = 0^{\circ}$ and $\sin\theta=0$. So, the magnetic force on the charged particle is zero.

Answer:

C. No force