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What is Power?

Power is an amount of energy supplied in a certain time.

Power is measured in watts. Energy is measured in joules.

1 watt = 1 joule per second.

The word "per" means "divided
by",

so power = energy ÷
time.
P =
E ÷ t.

Since 1
volt = 1 joule per coulomb

and
1 amp
= 1 coulomb per second

then watts
= volts x amps,

or power = voltage x current

P = V x I

The above equation
can be
rearranged to give

I = P
÷ V and V =
P ÷ I

On the next page
we shall see how to calculate the power

of any electrical component using a lamp as our example.

We can rearrange power =
energy ÷ time

to give energy = power
x time.
E = P x t.

Since power =
voltage x current (see above)

if we write V x I instead of
P

in the above equation we get
E = V x I
x t.

energy = voltage x current x time.

See all equations for electricity.

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