[" Ciealf,coction of the solenoid,and (iii) directly as sqyare of number of turns "(N)" in solenoid."],[" rea "A" of cross-section of the solenoid,and (iii) directly as sqyare of number of length "40cm," area of cross "],[" sample Problem What is the self inductance of a solenoid of length "40cm" ,area of cross "],[" fon "20cm^(2)" and total number of turns "=800?],[" Sol.Here,"L=?l=40cm=0.4m,A=20cm^(2)=20times10^(-4)m^(2),N=800]