1 ) When current in a coil changes to 8 ampere from 2 ampere in 3 x 10 ^ ( -3 ) sec , then emf induced in the coil is 2 volts . The self inductance of coil is . . . . . . . . . ?
A ) 10 ^ ( +3 )
Henry , B ) 10 ^ ( -3 )
Henry ,
C ) 10 ^ ( -6 )
Henry , D ) 10 ^ ( -9
) Henry
,
Correct
Answer : - B ) 10 ^ ( -3 ) Henry
,
Solution
: -
Formula
: -
We
have formula that : -
E =
d ( NΦ ) / dt = d ( LI ) / dt = L
. dI / dt ,
Ø E
= L . dI /dt ,
Ø 2
= ( L x 6 ) / 3 x 10 ^ ( -3
) ,
Ø L = 10 ^ ( -3 ) Henry
, Answer .
2 )
If in a coil rate of change of area is 15
m² / millisecond and current become 1 amp from 2 amp in 2 x 10 ^ ( -3 ) sec magnitude of field 1
Tesla , then self inductance of coil is . . . . . . . ?
A ) 7 Henry , B )
10 Henry ,
C ) 13 Henry , D )
None of these ,
Correct
Answer : - B ) 10 Henry ,
Solution
: -
So
we have formula : -
N Φ
= LI ,
so we take derivative : -
Ø N ( dΦ / dt )
= L . ( dI / dt ) ,
………… eq.1
So Φ = B.A ,
dΦ / dt = 1 . ( dA / dt ) ,
since ( B = 1 ) .
So put in eq .1 : -
Ø N.1.( dA / dt ) = L (
dI / dt ) , so put values ;
Ø (1 x 1 x 5) / 10^(-3) = (L
x 1) / 2 x 10^(-3) ,
Ø L = 10 Henry
, Answer .
