11(a)], |dB| = 0 There is an interesting  relation between e0, the permittivity of free
space; m0, the permeability of free space; and c, the speed of light in vacuum:
(
)
0
0
0
0
4
µ4
ε µ
ε
 
 
=
π
 
 
 
π 
 
(
)
7
9
1
10
9
10
−
 
 
=  
 
 
 
×
8 2
2
1
1
(3
10 )
c
=
=
×
We will discuss this connection further in Chapter 8 on the
electromagnetic waves Since the speed of light in vacuum is constant,
the product m0e0 is fixed in magnitude Choosing the value of either e0 or
m0, fixes the value of the other