Use the following to answer the next question N P S 20. What is the direction of the magnetic field at point P? A. C. -> B. D. Use the following diagram to answer the next question An ion of charge +le in a mass spectrometer enters the velocity selector region as shown below. The purpose of the velocity selector is to only allow ions having a specific desired velocity to pass through the selector undeflected. This is done by balancing the electrostatic and magnetic forces on ions which move with the desired velocity. The direction of the electric field is indicated by the arrows in the diagram. The magnetic field is not shown. Tube (cutaway view) + 9 Capacitor plates 21. Suppose the electric field across the plates of the velocity selector has magnitude 2.63 x 10' N/C. What is the necessary magnetic field which will allow ions of velocity 6.67 x 105 m/s to pass through undeflected? A. 4.21x 10-16 T [out of the page] C. 4.21x 10-16 T [into the page] B. 3.94 mT [out of the page] D. 3.94 mT [into the page] Version: B