ASHISH KUMAR
Last Activity: 3 Years ago
magnetic field for solenoid = B =

NI
and formula for self inductance is
N

= L I ( where L is self inductance )
and

(flux) = BACos

(

= 0 so Cos

= 1)
case 1 ) N (

NI * A) = LI
L =

N^2 A
case 2) now no of turn is doubled
so 2N (

(2N) I *A ) = L' I
L' = 4

N^2 A
hence Its new self inductance will be four times
option 1 Four times is correct