In Thomson's experiment on cathode rays, the speed of the cathode ray particles that were undeflected through perpendicular magnetic and electric fields was found to be 4.0 x 107 m/s. The magnetic field was measured to be 1.0 x 104 T and the corresponding electric field was provided by a charged parallel plate capacitor that had a separation of 2.0 cm. What was the potential difference across the plates? A proton travels through a magnetic field at a speed of 5.60 x 105 m/s perpendicular to the field. If the radius of the arc of the deflected proton is 7.50 mm, what is the magnetic field strength? (0.779 T) In a cathode ray tube, electrons are accelerated from rest by a potential difference of 1.40 kV. If these electrons enter a perpendicular magnetic field with a strength of 0.0220 T, what is the radius of arc for the deflected electrons?