Four particles enter a region of uniform magnetic field. Their trajectories are shown in figure. What are the signs of the charge of all four particles ?

Explanation

Particle A deflects to the right as it passes through the magnetic field, so we conclude that it is negatively charged. Particle B also deflects to the right, so it also must be negatively charged. Note that it may appear that particle B deflects opposite to particles A, but it is also traveling in the opposite direction. Particle C deflects to the left. so it is positively charged. Particle D travels along a straight line and so must be uncharged.