What objects experience a force in an electric field? Chapter 23 gives the answer: any electric charge, stationary or moving, other than the charge that created the field. What creates an electric field? Any electric charge, stationary or moving, as you studied in Chapter 23 What objects experience a force in a magnetic field? An electric current or a moving electric charge, other than the current or charge that created the field, as discussed in Chapter 29. What creates a magnetic field? An electric current, as you studied in Section 30.1, or a moving electric charge, as shown in this problem.
(a) To display how a moving charge creates a magnetic field, consider a charge q moving with velocity v. Define the vector r = r r to lead from the charge to some location. Show that the magnetic field at that location is
(b) Find the magnitude of the magnetic field 1.00 mm to the side of a proton moving at 2.00 x 107 m/s.
(c) Find the magnetic force on a second proton at this point, moving with the same speed in the opposite direction.
(d) Find the electric force on the second proton.

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