71. (a) We assume the current is changing at (nonzero) rate
di/dt
and calculate the total emf across both
coils. First consider the coil 1. The magnetic ±eld due to the current in that coil points to the right.
The magnetic ±eld due to the current in coil 2 also points to the right. When the current increases,
both ±elds increase and both changes in ﬂux contribute emf’s in the same direction. Thus, the
induced emf’s are
E
1
=
−
(
L
1
+
M
)
di
dt
and
E
2
=
−
(
L
2
+
M
)
di
dt
.
Therefore, the total emf across both coils is
E
=
E
1
+
E
2
=
−
(
L
1
+
L
2
+2
M
)
di
dt
which is exactly the emf that would be produced if the coils were replaced by a single coil with
inductance
L
eq
=
L
1
+
L
2
+2
M
.
(b) We imagine reversing the leads of coil 2 so the current enters at the back of coil rather than the
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.
 Fall '08
 SPRUNGER
 Physics, Current

Click to edit the document details