Electricity
Think how different your life would be without
electricity. Not only do we have vast energy
resources at our fingertips, but technologies
based on electricity like electronic
communication and computers have changed
the ways that people live.
EM
electron
proton
Neutron
electron repulsive attractive
None
proton attractive repulsive
None
neutron
none
none
None
We’ve studied the EM force between charged
particles, summarized in the table above. We
have also seen that metal atoms bond together
in such a way that electrons can move freely
through solid metal. Electrons can be forced
through a long thin piece of metal (a wire), and
we call this electric current. Forcing them in
one end causes current in the whole wire
because the EM force insures that electrons and
protons remain evenly distributed within the
wire.
one Coulomb is 6.24 million trillion. So in a wire
with one Amp of current, 6.24 million trillion
electrons pass a point each second.
Energy Per Charge
We use electricity to transport energy, and
there is a unit to express the amount of energy
per unit charge in electricity. One 𝑣𝑜𝑙𝑡 is one
𝐽𝑜𝑢𝑙𝑒 𝑝𝑒𝑟 𝐶𝑜𝑢𝑙𝑜𝑚𝑏. If a 6 volt battery is
connected in circuit to a light bulb, then every
Coulomb of charge that passes through the light
bulb will deliver 6 Joules of energy there.
Electrical receptacles in your home are designed
for 120 volt electricity. Every Coulomb of
charge that flows through a wire to for instance
your TV will deliver 120 Joules to make the TV
run.
High voltage does not necessarily mean a large
flow of energy. Charge coming from the Van
Der Graaff generator in the picture below has
about two hundred thousand volts.
Electric Current
The unit of electric charge is the 𝐶𝑜𝑢𝑙𝑜𝑚𝑏, and
an electron has −1.6 × 10−19 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 of
electric charge. The unit of electric current is
thus the 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑; one Coulomb
passes a point in a wire in one second. As with
a lot of units in physics, a name has been given
to the unit of current. One 𝐴𝑚𝑝𝑒𝑟𝑒 is the same
as one 𝐶𝑜𝑢𝑙𝑜𝑚𝑏 𝑝𝑒𝑟 𝑠𝑒𝑐𝑜𝑛𝑑. It’s more
commonly called the 𝐴𝑚𝑝. Since each electron
has the amount of charge indicated above, then
the number of electrons that contain a total of
That’s means that each Coulomb of charge
flowing into the child has 200,000 Joules of
energy. But the machine can only produce a
very small electric current.
Power
Since the Amp is one Coulomb per second and
the volt is one Joule per Coulomb, then if you
multiply them:
𝐴𝑚𝑝 ∙ 𝑉𝑜𝑙𝑡
𝐶𝑜𝑢𝑙𝑜𝑚𝑏
𝐽𝑜𝑢𝑙𝑒
∙
𝑠𝑒𝑐𝑜𝑛𝑑 𝐶𝑜𝑢𝑙𝑜𝑚𝑏
𝐽𝑜𝑢𝑙𝑒
𝑠𝑒𝑐𝑜𝑛𝑑
You get Joules per second. This is the rate of
energy flow. And it has its own name. One
1 𝑊𝑎𝑡𝑡 = 1 𝐽𝑜𝑢𝑙𝑒/𝑠𝑒𝑐.