c1 is a transistor / electrical regulator which allows electric current c2 = df1 to flow under conditions c3 in / on / through df2 flowing in direction to / towards df3 from direction/source df4.
c1 is an electromagnetic relay which allows electric current c2 = df1 to flow under conditions c3 in / on / through df2 flowing in direction to / towards df3 from direction/source df4.