48. It is desired to construct a solenoid that has a resistance of 5.00 (at 20C) and that produces a magnetic field at its center of 4.00 102 T when it carries a current of 4.00 A. The solenoid is to be constructed from copper wire having a diameter of 0.500 mm. If the radius of the solenoid is to be 1.00 cm, determine (a) the number of turns of wire needed and (b) the length the solenoid should have.