Flowing Charges | MCAT 2015
Conductors – objects through which
charge can flow
• Good conductors – allow free
movement of charge (i.e. metals)
• Poor conductors (aka resistors) –
restrict movement of charge (i.e.
plastic & wood)
…and placing another conductor
beside the first one will allow
those electrons to jump to the
new conductor…
…thereby giving the first
conductor a +2 charge.
Conductors & Resistors
The metal wire conducts electricity to electric
devices, while the plastic wire resists the
movement of charge, thereby confining the
electrons to the wire.
Induction – a method of charging a
conductor
• First, a conductor is placed
beside a strong negative charge...
…causing the conductor’s
electrons to move to the opposite
end of the conductor…
Current – unified flow of charge
• Originally defined as the flow of
positive charge
• Later learned to be the flow of
negative charge (electrons)
o Because of this mistake,
current flows in the
opposite direction of
electrons
Current vs. Actual Charge Flow
Though electrons actually flow clockwise (blue)
here (from the negative positive battery
terminal), current flows the opposite way (red).
•
Despite this error, current is still
an accurate measure of charge
flow
o A positive charge flowing
counterclockwise has the
same effect as a negative
charge flowing clockwise
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© 2016 J Co Review, Inc., Accessed by Guest on 09-29-2016
Flowing Charges | MCAT 2015
•
Current is actually a rate of flow
o Measured in
coulombs/sec, aka
amperes aka amps
Current as a Flow Rate
Current is the number of charges to pass through
an arbitrary point (red) in each second. Current is
thus measured in coulombs per second, or amps.
Motion of Charge in a Wire
o Though our diagrams often show
the wire much narrower than the
electrons, this isn’t really true
Wire is Much Thicker than Electrons
o Electrons have the freedom to
move around within the wire
o Their motion isn’t strictly
linear from left right
o Rather, they have some
random motion in all
directions (red), but their
overall uniform motion is
towards the right
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© 2016 J Co Review, Inc., Accessed by Guest on 09-29-2016