(This follows from the direct proportionality
between field and charge implied by Coulomb’s
law and the superposition principle ) Now,
potential difference V is the work done per unit
positive charge in taking a small test charge from
the conductor 2 to 1 against the field Consequently, V is also proportional to Q, and the
ratio Q/V is a constant:
Q
C
=V
(2 38)
The constant C is called the capacitance of the capacitor