One can use crossed electric and magnetic fields to construct a velocity selector, a device that only passes charged particles having a certain specified velocity. The diagram below shows one way of constructing such a velocity selector. We send an ion through a region of space where we have a uniform magnetic field perpendicular to the particles' velocity v and an electric field perpendicular to both B and i. Only ions having a specific speed will be able to travel in a straight line through this apparatus. Ion i B (a) Find an expression for the electric field strength | E| required to select a given speed || if the magnetic field inside the device has a magnitude | B|. Does your answer depend on the ion's mass m? Its charge q? (Hint: Assume that you can ignore gravity.) (b) Find the value of E| required to select protons with a speed of 0.01c if B| inside the device is 0.01 T. (c) Explain why can we ignore gravity in the case in part (b).