Electric current, circuits
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Electric current:
under influence of the electric field, mobile charges
will move towards positions of lower potential
energy;
 positive charges will move toward lower potential,
negative charges toward higher potential;
 a conductor is a material which has mobile charges;
 when a potential difference is maintained between
the ends of a conductor, charges will move
 “electric current flows”
 Current:
 electric current = ordered flow of electric
charge, = rate at which charge moves past a
reference point:
I = q/t
 unit of current =
1 Ampère = 1A = 1 Coulomb/second
 potential difference (voltage) can be maintained by
battery or other “voltage source” (often referred
to as “power source”)
electric circuit:
 = assembly of conductors, voltage sources and
other “circuit elements”
“Ohm's law”:
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relates the current to the applied voltage:
I = V/R, V = I R
current = voltage / resistance,
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Resistance, power
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power consumption in a circuit:
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where “resistance” is a measure for the opposition
against charge flow within the conducting material
(e.g. due to collisions with atoms, other charge
carriers,..)
unit of resistance = 1 ohm = 1  = 1 V/A
due to resistance, not all electric potential energy is
converted into kinetic energy of charge carriers and
eventually useful work - some (or all) of it is
“dissipated” as heat
when current is allowed to flow, charges move from
higher potential energy to lower potential energy;
total change in potential energy = amount of charge
moved x voltage = q · V;
this change in potential energy can be used to do work
and/or is converted into heat.
loss in potential energy has to be made up by energy
supplied from the power source;
power P = (energy converted) / time
=  q ·V /t = V ·(q/t) = V ·I
power = current x voltage
under the influence of a voltage ( electric
field) applied across a conducting medium, a
current (of positive charges) flows from higher
to lower voltage. The potential energy lost by
the charges is converted into work and/or heat,
and has to be replenished by the “power source”.