Download Ch 16.1 Electric Charge and Static Electricity

Ch 16.2 & 16.3 Current and
Circuits
• Electrical Potential Energy
– The amount of energy stored between two
charges
• Voltage
– Is the “push” behind making electrons
move
– Technically, the work it takes to move a
charge
– Measured in Volts (1J/C)
Voltage
• Batteries we used in class were 6V,
batteries in your calculator are
1.5V
• This means it would take 6 J to move
each Coulomb worth of charge…
but each electron is 1.6 x 10-19 C
• So each Volt can move a lot of
electrons
Current
• When the electrons move it is
called current
• If they flow in one direction, it is
called direct current (DC, e.g.
battery)
• If they move back and forth, it is
called alternating current (AC, e.g.
when you plug something in)
Amperage & Resistance
• A measure of the amount of
electrons flowing.
• Measured in Amps (A)
• As electrons move, they are
slowed down by friction. The
amount they are slowed is
resistance.
• Resistance is measured in
Ohms (W)
Like Water…
• So electricity is like flowing water:
– There’s something pushing the water or
some energy source making it flow
(push = voltage/volts)
– You can measure how fast it is flowing
(flow = amperage/amps)
– There are things that slow water down
(slowing = resistance/ohms)
• Conductors have low resistance and allow flow,
insulators have high resistance and block flow.
Semiconductors kinda allow flow.
Superconductors have almost no resistance at
very low temps (close to 0K).
Relationships
• For voltage staying the same:
– amperage and resistance are indirectly
proportional
– high slowing = low flow
• For current (amperage) staying the same:
– voltage must do whatever resistance does or
current will decrease
– If slowing increases, push must increase to
keep the same flow
Relationships
• For resistance staying the same:
– voltage must do the same thing as current
– You need a lot of push to keep a lot of flow
• Examples:
– voltage is high and current is low, resistance
is…
– voltage is low and resistance is high, current
is…
– current is high and resistance is low, voltage
is…
– Current is low and voltage is low, resistance is…
Circuits
• The actual pathway electrons flow
• Is like a circle…the electrons have
to go all the way around
• Schematics used to draw:
Series Circuits
• If there is only 1 way for the electrons to flow,
you have a series circuit
• If the circuit opens (by a switch or something
blows out) everything will go dead
• The lights are equally bright and will dim if you
add another (voltage is the same, but
resistance has increased so flow will decrease
Parallel Circuits
• If there are many pathways for electrons to flow, you
have a parallel circuit
• If the circuit opens (switch or blow out) some things
may still have current and work!
• Adding another light in parallel does not dim the
bulbs because you still have the same push, slow
and flow for each circuit!
Electrical Safety
• The amount of Power = voltage x
current
• Too much power = overload = fire!
• Grounding: providing a third wire to
the ground for electrons to flow
(third prong of plug)
• Fuse: metal that melts and opens
circuit if too much power
• Circuit breaker: magnet or strip of 2
metals that acts like a switch and
opens