4) implies:
Work done by an external force in bringing a unit positive charge
from infinity to a point = electrostatic potential (V ) at that point COUNT ALESSANDRO VOLTA (1745 –1827)
Count Alessandro Volta
(1745 – 1827) Italian
physicist, professor at
Pavia Volta established
that the animal electri-
city observed by Luigi
Galvani, 1737–1798, in
experiments with frog
muscle tissue placed in
contact with dissimilar
metals, was not due to
any exceptional property
of animal tissues but
was 
also 
generated
whenever any wet body
was sandwiched between
dissimilar metals This
led him to develop the
first voltaic pile, or
battery, consisting of a
large stack of moist disks
of cardboard (electro-
lyte) 
sandwiched
between disks of metal
(electrodes)