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Understanding
Electricity
Physical Science
Chapters 6,7,8,and 9
What is electricity?
 A form of energy that exists as an accumulation
of charge (static) or as the flow of charge
(current).
 These charges can be either protons (+) or
electrons (-).
VOCABULARY
 COULOMB - The unit of electric charge. The
quantity of charge conveyed in one second by
one ampere.
 AMP - One amp is a flow of one coulomb of
charge per second
 VOLT - One volt is an energy of one joule per
coulomb of charge
 OHM – The SI unit of electrical resistance. One
ohm of resistance exists in a circuit that has one
amp of current pushed by 1 Volt.
VOCABULARY
 CIRCUIT – A path through which electricity can
flow.
 CIRCUIT DIAGRAM – A drawing that uses symbols
to represent the real circuit.
Circuits
 Circuits are paths through
which electricity can flow.
 Open circuits are broken
circuits.
 Close circuits are
complete circuits.
Circuits, Symbols, and Circuit
diagrams
Types of circuits
 Series Circuits
 Only one
possible path
for current to
flow.
Characteristic of Series Circuit
Types of Circuits
 Parallel Circuit
 More than one
possible path for
current to flow.
Characteristic of Parallel Circuits
Series vs. Parallel
PROBLEM 1
 Observe the electrical wiring below. Indicate
whether the connections are series or parallel
connections. Explain each choice.
PROBLEM 1 ANSWER
Diagram A: Parallel
There is a branching location in the circuit that
allows for more than one pathway by which
charge can flow through the external circuit.
Diagram B: Series
There is no branching in the circuit - that is, no
location where one wire leads into a point and
branches off into two or more wires at that
particular point.
PROBLEM 2
 Two electric circuits are diagrammed below. For
each circuit, indicate which two devices are
connected in series and which two devices are
connected in parallel.
PROBLEM 2 ANSWER
 In Diagram A:
 SERIES: the ammeter and the resistor are in series
PARALLEL: the bulb and speaker
 In Diagram B:
 SERIES: the speaker and the ammeter
PARALLEL: the bulb and the resistor
Current
 Current is the “flow” of electrons, or electrons in
motion.
 Current is measured in a unit called amperes or amps
for short. The symbol for current is a capital i.
 Current is affected by the Voltage (push) and the
Resistance.
 Increasing the voltage will increase the current in a
circuit.
 Increasing the resistance will decrease the current in
a circuit.
CURRENT IN SERIES CIRCUITS
 The current in a series circuit is everywhere the
same. Charge does NOT pile up and begin to
accumulate at any given location such that the
current at one location is more than at other
locations.
 Total current (I) = I 1 = I 2 = I 3 = ...
KIRCHHOFF’S CURRENT LAW
 The same total current flowing into a branch
point has to flow out again.
Current in Parallel Circuits.
 The current outside the branches is the same as
the sum of the current in the individual branches.
 I total = I 1 + I 2 + I 3 + ...
Current in Parallel Circuits
OHM’S LAW
 OHM’S law states that the current in a circuit is
equal to the ratio of battery voltage to total
circuit resistance.
OHM’S LAW PROBLEM 1
 A light bulb with a resistance of 2 ohms is
connected to a 1.5 volt battery as shown.
Calculate the current that will flow.
OHM’S LAW PROBLEM 1 ANS
OHM’S LAW PROBLEM 2
 A light bulb requires 3 amps to produce light. The
resistance of the bulb is 1.5 ohms. How many
batteries do you need if each battery is 1.5
volts?
OHM’S LAW PROBLEM 2 ANS
Types of current
 Alternating current (AC): Current that flows in
more than one direction in a wire.
 Produced at power plants and sent out to your
home.
 We use AC adapters to change current into DC.
 Direct current (DC): Current that flow in only one
direction in a wire.
 Produced by batteries.
Voltage
 Voltage is the “push” that causes electrons to
move.
 It is the difference in electrical potential energy
between the two places where electrons are
flowing.
 Electric potential is a location dependent
quantity which expresses the amount of
potential energy per unit of charge at a
specified location.
VOLTAGE
 The standard metric unit on electric potential
difference is the volt, abbreviated V and named
in honor of Alessandra Volta.
 One Volt is equivalent to one Joule per
Coulomb.
 If the electric potential difference between two
locations is 1 volt, then one Coulomb of charge
will gain 1 joule of potential energy when moved
between those two locations.
VOLTAGE
 if the electric potential difference between two
locations is 12 volts, then one coulomb of charge
will gain 12 joules of potential energy when
moved between those two locations.
 BELOW ARE A COUPLE OF EXAMPLES:
VOLTAGE IN SERIES CIRCUITS
 VOLTAGE DROP in a series circuit is equal to the
total voltage drop across each resistor in the
circuit.
 ΔV battery = Δ V1 + Δ V2 + Δ V3 + ...
KIRCHHOFF’S VOLTAGE RULE
 Around any circuit, the voltage changes must
add up to zero.
VOLTAGE IN SERIES CIRCUITS
VOLTAGE IN SERIES CIRCUITS
VOLTAGE IN SERIES CIRCUITS
PROBLEM 3
 Determine the voltage drop for the two light
bulbs.
RESISTANCE
 Resistance is the ability of an object to conduct
current.
 If objects have a high resistance, they are called
insulators.
 If objects have a low resistance, they are called
conductors.
RESISTANCE
RESISTANCE IN SERIES
CIRCUITS
 The act of adding more resistors to a series circuit
results in the rather expected result of having
more overall resistance. Since there is only one
pathway through the circuit, every charge
encounters the resistance of every device; so
adding more devices results in more overall
resistance. This increased resistance serves to
reduce the rate at which charge flows (also
known as the current).
RESISTANCE IN SERIES
CIRCUITS
 There is a clear relationship between the
resistance of the individual resistors and the
overall resistance of the collection of resistors. As
far as the battery which is pumping the charge is
concerned, the presence of two 6-Ω resistors in
series would be equivalent to having one 12-Ω
resistor in the circuit. The presence of three 6-Ω
resistors in series would be equivalent to having
one 18-Ω resistor in the circuit. And the presence
of four 6-Ω resistors in series would be equivalent
to having one 24-Ω resistor in the circuit.
RESISTANCE IN SERIES
CIRCUITS
Total Resistance = R1 + R2 + R3 + ...
RESISTANCE IN SERIES
CIRCUITS
SHORT CIRCUITS