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KEAM 2021 Physics and Chemistry Solved Paper
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© examsnet.com
Question : 15
Total: 120
If air core is replaced by an iron core in an inductor, its self-inductance is increased from
0.02
m
H
to
40
m
H
. The relative permeability of iron is
5000
2000
200
500
400
Validate
Solution:
Inductance of a solenoid coil of length
L
, total number of turns
N
and cross-sectional area
A
, is given as
L
=
µ
0
N
2
A
l
....(i)
where,
µ
0
is the permeability in vacuum (or air).
If air core is replaced by iron core, inductance will be given as
L
′
=
µ
N
2
A
l
....(ii)
On dividing Eq. (ii) by Eq (i). we get
L
′
L
=
µ
N
2
A
l
/
µ
0
N
2
A
l
=
µ
µ
0
=
µ
r
where,
µ
r
is the relative permeability of iron. Given,
L
=
0.02
m
H
,
L
′
=
40
m
H
∵
µ
r
=
40
0.02
=
2000
© examsnet.com
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