It is desired to construct a solenoid that will have a resistance of 4.10 ω (at 20°c) and produce a magnetic field of 4.00 ✕ 10^−2 t at its center when it carries a current of 3.95 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 the following. (the resistivity of copper at 20°c is 1.7 ✕ 10^−8 ω · m.) (a) the number of turns of wire needed to build the solenoid turns (b) the length the solenoid should have.