physics help PLEASE!?

Question

hello, does anyone know how to derive the expression of the electric field from the magnetic field, mass, and velocity?

Update:

by the way it’s asking for the expression of the electric field between the two plates

Answer 1

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Let's say the particle has mass m, charge q, and leaves the parallel plate region with a speed v.  Then

 F = qvB*sin(x) = mv^2/r  x = 90 deg (angle between B and v) so

  r = mv/(qB)  or v = qBr/m  or B = mv(qr)

In the region of the parallel plates the charge has no net force acting on it so

F = 0 =qE + qvB  -->  E = -vB = -mv^2/(qr)

Since I'm not sure what the given parameters are  (e.g. do you know B?) this  is the best I can do.