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Problem 2 A long cylindrical wire of radius R carries a current density J(r) that varies as a function of the radius r, given by r R2. R2 J R1 (a) Given J(r), find an expression for lenc as a function of radius. Remember to find lenc within all three regions. (Hint: Use the fact that Ienc = f J . dA, and in this case dA = 2mr dr, so Ienc(r) = 27 So J(r') r'dr'. ) (b) What is the magnitude of the magnetic field for r R2