Transcript Direct Current and Alternating Current. Series Circuits and Parallel

Direct Current (DC) and Alternating
Current (AC).
Series Circuits and Parallel Circuits.
Direct Current (DC)
• Direct Current is a flow of
charge that always flows
in one direction
• A DC current is a current
that does not change
direction in time.
• A battery produces direct
current in a circuit.
Example: Portable
flashlight circuit.
Alternating Current (AC)
• An Alternating Current
(AC) current is a current
that changes direction in
time.
• If the high & low voltage
terminals switch locations
periodically, the current
will flow back and forth in
the circuit. This is called
alternating current (AC).
Alternating Current
• In alternating current (AC) electrons in a
circuit move in one directions and then in
opposite direction, alternating back and forth
about relatively fixed position.
• Alternating current is accomplished by
alternating polarity voltage at the generator
or other voltage source.
• AC current flows in your home.
AC in the USA
• In public power distribution systems in the
United States, (including household current),
the voltage reverses itself 60 times per
second. In some countries, the voltage
reverses itself 50 times per second.
• Normal outlet voltage in the US is 110-120
volts, although some large household
appliances run on 220-240 volts.
Converting AC and DC
• The current in your home is AC.
The current in a battery
operated device is DC. AC is
converted to DC using devices
called diodes, which allow
charges to move in only 1
direction.
• Diode is a tiny electronic device
that acts a one way valve to
allow electron flow in only one
direction.
• Because alternating current
vibrate in two directions , only
half of each cycle will pass
through a diode. A capacitor is
used to have continuous
current.
Series and Parallel Circuits
• Series Circuits:
only one end of each
component is connected
Example: Christmas tree
lights
• Parallel Circuits:
both ends of a component
are connected
Example: household
lighting
Series Circuits
Series circuit:
• All in a row
• Current has one path for
electrons
• Current flows through every
part of the circuit
• 1 light goes out and the
circuit is broken
Adding Resistor to Series
• If you add a resistor (like another
light):
• Total resistance goes up since all the
current has to go through each
resistor.
• If you remove a light bulb or one
burns out—all go out!
Current, Voltage, and Resistance in
Series
• Current is the same at all points
• Use Ohm’s Law to find current using resistance
and voltage
• I=
𝑉
𝑅
• Voltage is reduced by each resistance – voltage
drop
• Add up all resistors to get total
• Total resistance will go up because all of the
current must go through each resistor.
Parallel Circuits
Parallel circuit:
• More than one path for
current to flow
• Paths are also known as
branches
• Has at least one point
where current divides
• 1 light goes out and the
others stay on
Parallel Circuits
• If you add a resistor:
–Total resistance goes down
–Total current goes up when you
add another path
• If you remove a light bulb or one
burns out, the others stay on
because the circuit is still closed.
Current and Voltage in Parallel Circuits
• Current flows into a branching point, the same
total current must flow out again
• Current depends on resistance in each branch
• Voltage is the same across each branch –
because each branch is on the same wire
Series and Parallel Circuits
• Series Circuit: Current is
the same at all points in
the circuit.
• Parallel Circuit: Current is
shared between the
components
• Adding resistor in series
increases resistance and
slows the current flow.
• Adding resistor in parallel
lowers resistance and
increases the current
flow.