42)
Hence, the potential difference between the terminals A and C of the
combination is
( )
( )
( )
( )
AC
(A)–
(C)
A –
B
B –
C
V
V
V
V
V
V
V
≡
=
+
 
 
 
 
 
 
 
 
       
(
)
(
)
1
2
1
2
– I r
r
ε
ε
=
+
+
(3 43)
If we wish to replace the combination by a single cell between A and
C of emf eeq and internal resistance req, we would have
VAC = eeq– I req
(3 44)
Comparing the last two equations, we get
  eeq = e1 + e2
(3 45)
and  req = r1 + r2
(3