Electricity
• Electric Charge- property that causes
subatomic particles such as protons and
electrons to attract or repel each other
• An excess or shortage of electrons produces a
net electric charge
• Like charges __________, and opposite
charges __________
• Electric Force- force of attraction or repulsion
between electrically charged objects.
Charles-Augustin de Coulomb
• French scientist (17361806)
• Coulomb’s Law- the electric force between
two objects is directly proportional to the net
charge on each object and inversely
proportional to the square of the distance
between them.
• Coulomb- SI unit of charge= 6.24 x 1018
electrons or protons
• F=K(qAqB/r2)
• Coulomb’s Constant (K)= 9.0 x 109 Nm2/C2
Coulomb’s Law Example Problem #1
• A negative charge of -2.0 x 10-4 C and a
positive charge of 8.0 x 10-4 C are separated by
0.30 m. What is the force between the two
charges?
Coulomb’s Law Example Problem #2
• Sphere A, with a charge of 6.0 μC, is located
near another charged sphere, B. Sphere B has
a charge of -3.0 μC and is located 4.0 cm to
the right of A
– What is the force of sphere B on A?
– A third sphere, C, with a 1.5 μC charge, is added to
the configuration. If it is located 3.0 cm directly
beneath A, what is the new net force (magnitude
and direction) on sphere A?
• Electric Field- the effect an electric charge has
on other charges in the space around it
• The strength of an electric field depends on
the amount of charge that produces the field
and on the distance from the charge
• Static Electricity- An accumulation of electric
charge on an insulated body
• Electrostatics- the study of electric charges
that can be collected and held in one place
charge can be transferred by friction, contact
and by induction.
• Law of Conservation of Charge- whenever
there is a charge transfer, the total charge is
the same before and after the transfer occurs.
The total charge in an isolated system is
constant
Charging
Friction
Definition:
Examples:
Contact
Induction
• Static Discharge- occurs when a pathway
through which charge can move forms
suddenly
• Insulator- a material through which a charge
will not move easily
– Glass, dry wood, plastics, cloth, dry air
• Conductor- a material that allows charges to
move about easily
– Metals, plasma, graphite
Electroscope
• Myth Buster's Van de Graaff Generator
Electric Current
• Electric current- continuous flow of electric
charge
• Ampere (A)-AKA amp- SI unit of electric
current
– 1 Amp= 1 Coulomb per second
• The 2 types of current are direct current and
alternating current
– Direct current- charge flows only in one direction
– Alternating current- flow of electrons that
regularly reverses its direction.
• Electrons flow from the negative terminal of
on battery to the positive terminal of the
other battery, but the current is in the
opposite direction because it is defined as the
direction in which positive charges would flow
Resistance
• Resistance- opposition to the flow of charges
in a material
• Ohm- SI unit for resistance
• A material’s thickness, length, and
temperature affects its resistance.
• Superconductor- a material that has almost
zero resistance when it is cooled to low
temperatures
Voltage
• In order for charge to flow in a conducting
wire, the wire must be connected in a
complete loop that includes a source of
electrical energy
• Potential difference- AKA Voltage- the
difference in electrical potential energy
between two places in an electrical field.
• Volts- SI unit for potential differenceJoules/Coulomb
Voltage Sources
• Battery- a device that converts chemical
energy to electrical energy
Ohm’s Law
• Georg Ohm- (17891854)
• Published research in
1826- so controversial
that he was fired!
• V=I x R
• Voltage in a circuit
equals the product of
current and the
resistance
• I=V/R
• Increasing the voltage __________ the
current. Keeping the same voltage and
increasing the resistance __________ the
current.
Electric Circuits
• Electric Circuit- a complete path through
which charge can flow
• Circuit diagrams- use symbols to represent
parts of a circuit, including a source of
electrical energy and devices that are run by
the electrical energy.
– Open circuit: Switch open
– Closed circuit: Switch closed
• How is the direction of current defined?
• Series circuit- charge has only one path
through which it can flow.
– If one element stops functioning in a series circuit,
none of the elements can operate
• Parallel circuit- electric circuit with two or
more paths through which charges can flow
– If one element stops functioning in a parallel
circuit, the rest of the elements still can operate
Electric Power and Energy Calculations
• Electric power- the rate at which electrical
energy is converted to another form of energy
• Watt- Joule/second
• P(watts)=I(amps) x V(volts)
Power Example
• A clothes dryer uses about 27 amps of current
from a 240 volt line. How much power does it
use?
Electrical Energy
• E= P x t
• Kilowatt-hour- SI unit of electrical energy=
3,600,000
Electrical Safety
• Correct wiring, fuses, circuit breakers,
insulation, and grounded plugs help make
electrical energy safe to use
• Fuse- prevents current
overload in a circuit
• A wire in the center
melts if too much
current passes through
it- “blowing a fuse”
• Circuit breaker- switch
that opens when
current in a circuit is too
high
• Grounding- transfer of
excess charge through a
conductor to Earth
• Ground Fault Circuit
Interrupter (GFCI)monitors current
flowing to and from an
outlet or appliance