試題詳解

58. The figure shows a velocity selector that can be used to measure the speed of a charged particle. A beam of particles is directed along the axis of the instrument. A parallel plate capacitor sets up an electric feld E, which is oriented perpendicular to a uniform magnetic field B. If the plates are separated by 2.0 mm and the value of the magnetic field is 0.90 I, what voltage between the plates will allow particles of speed 5.0x10⁵ m/s to pass straight through without deflection?
(A) 900V 
(B) 1900 V
(C) 3800 V
(D) 190 V
(E) 94 V Capaeitor xxxxx plates