Find the energy stored in a section of length l of a long solenoid (radius R. current I, n tums per unit length),

(a) Using Eq. 7.29 (you found L in Prob. 7.22);

(b) Using Eq. 7.30 (we worked out A in Ex. 5.12);

(c) Using Eq. 7.34;

(d) Using Eq. 7.33 (take as your volume the cylindrical tube from radius a < R out to radius b > R).