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An electrostatic force of 5 N exists between two identical point charges, each of mass 0.01 g, placed 4 mm apart.

a.) Find the magnitude of each charge.

b.) One of these charges is placed into a magnetic field. Assuming that the charge has a speed of 50 m/s and travels a circular path of radius 5 mm, what is the strength of the magnetic field?

c.) Now the charge is removed and a 0.5 m long wire is placed into the magnetic field from part b. What magnitude current would have to pass through the wire in order for it to feel the same magnetic force as the charges in part a?

(a) Use the Coulomb force formula for the force acting on each of two charges.
F = k Q1 Q2/R^2
In your case Q1 = Q2 = Q, and R = 0.004 m. Look up k is you don't kow what it is. Solve for Q.

The mass won't matter in the answer to (a).

(b) This time the mass matters. Set the centripetal force m V^2/R equal to the magnetic force q V B. Thet is what keeps the particle moving in a circle.
Solve for the megnetic field B, in units of Tesla. Make sure R = 0.005 m this time.

(c)Force on a wide of length L, carrying a current I perpendicular to a field B is
F = B I L. Set this equal to the 5 N force of part (a). Solve for I

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