
27-1
Electric charge, a basic property of elementary particles, is dened by convention as negative for the
electron and positive for the proton. In 1910, Robert Andrews Millikan (1868–1953) demonstrated the
qu
antization
an
d
de
termined
th
e
va
lue
of th
e
el
ementary
ch
arge
by me
asuring
th
e
mo
tion
of sm
all
ch
arged
dr
oplets
in an ad
justable
el
ectric
e
ld
. e SI un
it
of ch
arge,
th
e
co
ulomb
(C
),
is de
ned
in te
rms
of b
ase
S
I
u
nits
a
s
1 c
oulomb
= 1 a
mpere
× 1 s
econd
(2
7
.1a
)
In terms of fundamental physical constants, the coulomb is measured in units of the elementary
ch
arge
e:
1C = 1.60217733 10
19
× e
(27.1b)
where
t
he
r
elative
u
ncertainty
i
n
t
he
v
a