P which equals VI, can be expressed in two other ways.
Since
V = IR
then
P = IRI = I
2
R
Since
V
I = -
R
then
V V
2
p=V- = —
R R
The main units used are
1 The watt (W)
2 The megawatt (MW) = 10
6
W
3 The kilowatt (kW) where 1 kW = 10
3
W
4 The milliwatt (mW) where
1
mW = 1/10
3
W =
10
~
3
W
5 The microwatt (u.W) where 1 fiW = 1/10
6
W = 10"
6
W
It therefore follows that 1 MW = 10
3
kW. The relationships
between the subunits are the same as those for voltages, covered in
Chapter 1, and for current, covered in Section 3.2.
3.5 Types of circuit ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month, and much more.