A charged particle enters at right angles into a uniform magnetic field as shown. What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field ?

Quick Oral Answer

The particle should be positively charged because the force on a charged particle in a magnetic field is given by the right-hand rule. If the particle moves in a direction pointing vertically out of the page, then the force must be directed in the same direction. Since the magnetic field is uniform and the particle enters at right angles, the force will be perpendicular to both the magnetic field and the velocity of the particle. Using the right-hand rule, we can see that the force will be directed out of the page if the particle is positively charged.