- Two oppositely charged parallel plates are a distance 8.0 cm apart. The potential difference between the plates is 120 V. An alpha particle is placed on the positively charged plate and released from rest. Gravity is ignored.
parallel‑plate diagram with 8.0 cm separation and 120 V potential difference
(a) Calculate the electric field between the plates. [1]
(b) (i) Show that the acceleration of the alpha particle is about 7 × 10¹⁰ m s⁻². [2]
(ii) Calculate the time taken for the alpha particle to reach the negative plate. [2]
(iii) State, in eV, the kinetic energy of the alpha particle when it arrives at the negative plate. [1]
(c) A magnetic field directed into the plane of the page is now established between the plates. An alpha particle enters the region between the plates with a horizontal speed of 5.0 × 10⁵ m s⁻¹. The particle is not deflected.
parallel‑plate diagram with magnetic field (crosses) into the page
Calculate the magnitude of the magnetic field. [2]
(d) The alpha particle in (c) is replaced by an electron. The electron enters the region between the plates with the same velocity as the alpha particle. Draw, on the diagram, the path of the electron. [1]