The
current
from
a
cell
is
____________________
____________________
,
a
constant
flow
of
electricity
which
travels
around
a
circuit
in
one
direction
.
The
electricity
supplied
to
homes
and
other
buildings
,
called
____________________
____________________
,
is
____________________
current
.
Unlike
DC
supply
,
an
AC
supply
flows
backwards
and
forwards
(
its
direction
continually
alternates
)
.
The
rate
at
which
the
current
alternates
,
called
the
____________________
,
is
measured
in
____________________
.
For
example
,
in
the
UK
,
AC
supply
is
50
Hz
,
it
alternates
50
times
per
second
.
On
a
graph
,
the
AC
supply
of
mains
electricity
forms
a
sine
wave
.
The
current
supplied
to
most
homes
is
____________________
-
____________________
,
it
forms
one
single
wave
.
In
factories
and
large
buildings
,
which
have
powerful
electrical
equipment
,
the
supply
is
often
____________________
-
____________________
,
effectively
three
currents
,
each
with
a
different
phase
(
timing
)
.
This
provides
a
smoother
supply
as
it
reduces
the
gaps
between
the
voltage
peaks
.
