You wish to design a velocity selector (see figure below) that will allow proton

Question

You wish to design a velocity selector (see figure below) that will allow protons to pass through only if they have a speed of 548 m/s. +q traveling eastward, electric field directed upward, and magnetic field directed down/west ward at 45 degree angle of the electri field, F(electric) upward, and F(magnetic) downward. a) If the magnetic field is B = 0.055 T, what electric field do you need? ____________________ N/C b) You decide to produce this electric field using a parallel-plate capacitor with a plate spacing of 11 mm. What is the electric potential across the plates? ____________________ V c) Will your velocity selector work for Li+ ions? 1. Yes 2. No ____________________ d) Will your velocity selector work for Mg2+ ions? 1. Yes 2. No

Explanation / Answer

Part A:

F = Fb = qvB = Fe = Eq

==> E = vB = 548*0.055 = 30.14 V/m

Part B:

V = Ed = 30.14 *0.011= 0.33154 V

Part C:

Yes

Part D:

Yes

The selector works for any charge, any mass. It simply compares a particle's velocity-dependent force with its velocity-independent force and selects the particles that experience equal forces.

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