7 A circle centered at the origin, with radius R, is carrying a steady current I in the direction shown. What is the magnitude AND direction of the magnetic field at (0,0,z) in this coordinate? (b) A solenoid can be constructed by putting a lot of rings next to each other. Use the result in (a) to derive the formula for the B-field of an "ideal" solenoid. i.e. to evaluate the magnetic field at the center of an ideal solenoid made of infinite rings packed closely together, such that there are n turns ner unit length along the z-axis. (M12b Sp18 2)

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