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Section 2
Current
Voltage and Current
• Electrical Potential Energy: the ability
to move an electrical charge from one
point to another.
• Depends on position in the electric field
Potential Difference
• Potential Difference- between any two
points the work that must be done
against electric forces to move a unit
charge from one point to another
• Measured in volts (V)
• Common unit used for batteries
Voltage in batteries
• Batteries help power many things in our
daily lifes
• Range from 1.5 V to 12 V
• Cell: a device that is a source of electric
current because of a potential difference
or voltage between the two terminals
Dry and Wet cells
• Batteries contain an electrochemical cell.
• Each cell has an electrolyte and two
electrodes on either end
• Dry cells have a paste like electrolyte
that helps conduct electricity
• Wet cells contain a liquid electrolyte
Dry vs. Wet cell
Current
• Electricity flows from the negative to the
positive terminal
• Current: The rate that electric charge
moves through a conductor
• Measured in ampheres
Electrical Resistance
• Resistance: the opposition posed by a
material or device to the flow of a
current.
• Conductors have low resistance
• Insulators high resistance
Resistance Equation
• resistance = voltage/current
• R= V/I
• SI unit is ohm Ω (greek letter omega)
• Resistor special kind of conductor used to
control the rate of flow in an object
Resistance Problem
• The headlights of a typical car are
powered by a 12 V battery. What is the
resistance of the headlights if they draw a
3.0 A pf current when turned on?
Example problem
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Current = 3.0 A
Voltage = 12 V
Resistance =?
Equation R= V/I
R= 12 V/ 3.0A
R= 4.0Ω
Try this one
• Find the resistance of a portable lantern
that uses a 24 V power supply and draws
a current pf 0.80 A?
Solution
• R= V/I
• R= 24V / 0.80 A
• R= 30Ω
Superconductors
• Metals that have zero resistance when
they fall below certain temperatures
• Temperatures range from -272°C to 123° C
• Used in filters, magnets and high speed
trains
Semiconductors
• Contains properties of both conductors
and insulators
• In a pure state semiconductors are
insulators
• Controlled amounts of materials added
to the semiconductor control its ability
to conduct an electrical charge
• Common examples- computer boards
Circuits
Section 3
Warm-up
• Discuss amongst your group which circuit
would conduct the most electricity: A
parallel circuit or an open circuit
Electrical circuits
• When we want to light a lightbulb with
wires and a battery all the parts must be
connected in order for electricity to flow
• A set of electrical components
connected such that they provide one
or more complete paths for the
movement of charges
Closed circuits
• Circuits that provide a closed loop for
electricity to flow around
• Occurs when the wires are connected to
the battery and the lightbulb in a closed
loop
Open circuit
• When one part of the circuit is missing
the electricity can not flow
• This type of circuit is called an open circuit
Switches
• When applied to a circuit you can
switch the circuit from open to closed
• When the lights are on the circuit is closed
when they are off the circuit is open.
Schematic designs
• A graphical representation of a circuit
that uses lines to represent wires and
different symbols to represent
components
• Because schematic devices use
standard symbols they can be read by
people all over the world.
Series circuit
• The components of a circuit that form a
single path for current
• Since there is only one path for the
electricity to flow the time it takes to
charge this item is the same
Parallel circuit
• A circuit in which all of the components are
connected to each other side by side
• The current in each item doesn’t have to
be the same.
• Even if we remove a bulb from the circuit
the other light bulb would light
Electrical Energy
• The energy that is associated with
charged particles because of their
positions
• Electric power: rate at which electric
energy is used in a circuit
Electrical Power Equation
• Power = current x voltage
• P=IV
• SI Unit watt (W)
Example
• When a hair dryer us plugged into a 120 V
outlet it has a 9.1 A current in it. What is
the hair dryer’s power rating?
Steps to solve problem
• V= 120V
• I = 1.9 A
• P= VI
• P= 120 x 1.9
• P= 1.1 x 10 ^ 3 W
Try this one
• An electric space heater requires 29 A of
120 V current to adequately warm a room.
What is the power rating of the heater?
Solution
• P= VI
• P= 120 X 29
• P= 3480 W