Transcript Basic Circuit Ideas

Moving Electricity
If charges in a conductor (like a metal)
are connected to a battery or source of
electric potential difference, they will
move.
Electric Current



Current is the movement or flow of
charges.
Current = I = charges/time =
coulombs/sec = amps
1 Amp of current is a lot of current
(relatively speaking)
Electric Current & People







Range of current and its affects on humans
1 mA (.001A) Slight tingling
5 mA (.005A) Slight shock, disturbing
6-30 mA painful shock, muscle control lost
50-150 mA Extreme pain, resp. arrest. Death possible
1000-4300 mA Death likely, rhythmic pumping of heart
ceases
The good thing is our bodies have a lot of resistance
(100,000 ohms – ish) so we have lots of resistance to
current flow (but, our resistance goes down if we’re wet
or wearing copper clothing)
Ohm’s Law: resistance & resistors





To produce a current a “difference in
potential” is required (voltage) .
The Current (I) which flows in a conductor
is proportional to this Voltage (V).
The Resistance of the circuit also
influences the flow of charge.
Ohm’s Law: V = I R
R = resistance = ohms Ω
Resistors




Resistors resist the flow of current.
Resistors are used in circuits to control or
regulate the amount of current
Many simple electrical devices are simple
resistors, examples include hot glue guns,
waffle irons, clothes irons, toasters.
In these examples resistors heat up as
they absorb energy provided by the
moving charges.
Resistivity



The resistance of a material depends on
its geometry and the type of material its
made of.
Resistivity is a property of a material
which tells you how much it resists current
flow. The symbol is ρ.
R (resistance) = ρL/A where L = length of
the conductor and A is the cross-sectional
area.
Resistivity
Material
Copper
Gold
Iron
Waffle
Resistivity
1.68 x 10-8
2.44 x 10-8
9.71 x 10-8
812 x 108
Electric Power





Watt?, not another electricity topic
Electric Power = energy used per time
P = J/sec = ? (yes)
For electricity, P = VI = I2R = V2/R
Many electrical devices are rated by their
power usage. For example, a 100W bulb
uses 100 joules/sec.