Self Induction

When there is change in current through a solonoid then there will be induced emf in opposite direction of cause which produces it. This process is called as self induction
Now flux linked with the coil of solonoid
φ α I
φ = LI----------1 where L is called inductance of coil
Now we have
e = -dφ/dt
e = -d(LI)/dt
= -LdI/dt--------2
If dI/dT = 1amp/sec
Then e=L
Hence inductance of a solonoid can be defined as the back emf induced when the rate of change of current is 1 unit

Self inductance of a solonoid
Let a solonoid of length L having total no, of turns of coil N
Let Current I passes through it
then B = UonI
= UoN/l *I

φ = BAN
= UoAN^2I/L
we have
L = φ/I = UoAN^2/L