Figure 28-22 shows three situations in which a positively charged particle moves at velocity$\overrightarrow{\mathbf{V}}$through a uniform magnetic field $\overrightarrow{\mathbf{B}}$and experiences a magnetic force$\overrightarrow{{\mathbf{F}}_B}$In each situation, determine whether the orientations of the vectors are physically reasonable.

Use the right hand rule to find the direction of force. For the possible orientation, with three vectors mutually perpendicular. From this, predict whether the orientation of the vectors is physically reasonable or not in the given figures.

For fig. (a) Orientation of vectors is not possible because velocity$\overrightarrow{V}$is not perpendicular to magnetic force$\overrightarrow{F_B}$.

For fig. (b) Orientation of vectors is possible because force$\overrightarrow{F}$is perpendicular to velocityand magnetic field$\overrightarrow{B}$.

For fig. (c) Orientation of vectors is not possible because velocity $\overrightarrow{B}$is not perpendicular to magnetic force $\overrightarrow{F_B}$

Hence, the orientation of vectors in figure(b) is the only physically reasonable vectors.

Therefore, using the right hand rule find the direction of force, and it must be perpendicular to both velocity and magnetic field.