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Page 1

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Introduction
Electricity is NOT a source
of energy. It is just a
convenient way of
TRANSFERRING energy
from one place to another
with relatively little energy
loss.

Page 2

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Introduction
TAP HERE

...for a video on Charge
and Current.

Page 3

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Introduction
Electric current is a
measure of the flow of free
electrons.
Electric Potential (a.k.a.
Voltage) is a measure of
how closely those
electrons are packed
together.

Page 4

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Free Electrons
The outer electrons
orbiting the atoms of
metals can be forced out
of orbit and made to drift
through the atomic lattice.
If a very large number of
such electrons all move at
once then this forms an
electric current.

Page 5

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Electric Current
Electric current is the rate
of flow of charge
I = Q/t
1 Ampere (A) is 1 Coulomb
(C) per second (s)
1 A = 1 Cs-1

Page 6

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The Coulomb
1 Coulomb is the amount
of electrical charge
transferred when a
constant current of 1 Amp
flows for 1 second.
Q = I x t

Page 7

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Electric Current
Since each electron has a
charge of 1.6x10-19
coulombs (C) then a
current of 1 Amp is also a
flow of 6.25x1018 electrons
passing a fixed point every
second.

Page 8

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Electric Current
The direction of electric
current flow is defined in
terms of the flow of
positive charges ­ this is
"conventional current".
Electrons flow in the
opposite direction.

Page 9

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Electric Current



A wire has length L,
cross-sectional area A and
contains n charge-carriers
per unit volume and each
has a charge q

Page 10

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Electric Current



So the total charge, Q
contained in this section of
wire is nq x volume.
Q=nALq.

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