Transcript electrical current - Fulton County Schools

Electricity &
Magnetism
Where science and magic meet
Electricity
• is the flow of electrons, described
as an electrical current.
• Electrons are negative, so the
electrons move from a negative
pole towards a positive pole.
• Electricity can be described as the
forces between charges.
Circuits
• A circuit describes the path that
electrons flow through.
• If there is a break in the circuit, the
electric current will not flow.
Circuits
• An incomplete or broken circuit is
said to be an “open circuit”.
• A complete circuit is called a
“closed circuit”.
• Switches are devices designed to
make a circuit open or close.
Oops!
• A short circuit occurs when the
electrical current finds a “short cut”
across the circuit.
• When this happens, the electricity
jumps across the path of least
resistance, and the designated
work, or load, is not accomplished.
What about it?
• While the study of electricity is
relatively new (less than 200
years), a great deal of
investigation has been done
recently
• Due to innovations in the modern
electrical world (1920 –)
Charges
• A charge is a point source of
electrical force.
• There are only two charges;
Positive and Negative.
Rule of Charge
• The Rule of Charges is stated:
“Opposites Attract, Likes Repel”
Charges in the world
• Most common objects are neutral
(having the same number of + and
– charges)
• An object which has more of one
charge than another is said to be
charged.
Shocking!
• The buildup of charges on an
object is static electricity.
• When the static charges do move,
it is called an electrical discharge
(the charges move along the path
of least resistance).
Shazam!
• Lightning is a form of electrical
discharge.
• The static charges are formed
when the particles inside the storm
cloud rub against each other,
separating charges.
Lightning
Lightning
How to charge
• Induction
– Bringing a charged object near an
uncharged object causes the like
charges to run away and attracts the
opposite charges
– Give the like charges an “out”,
leaving the opposites
How to charge
• Conduction
– Touching a charged object to an
uncharged object causes the
charges on the charged object to
spread through the two objects
Voltage
• Amount of PE that each unit of
electrical charge has
• V= I x R
• Voltage (volts)=Current (amperes)
x Resistance (ohms)
Power
• Power is measured in Watts (W)
• Power = Voltage x Current
• W=Volts x Amps
Ohm’s Law
• Describes the mathematical
relationship present in most
circuits
Current
• Quantity that refers to the rate of
flow of electric charges
• I = V/R
• Current = Voltage/Resistance
• Amps = Volts/ohms
Resistance
• Conductor – allows the flow of
electrons
• Insulator – DOES NOT allow the
flow of electrons
Resistance
• The measure of an object’s ability
to conduct electrical current
• R = V/I
• Resistance = Voltage/Current
• Ohms = volts/amps
What is the
difference between
placing a 1.5 V
battery or a 9 V
battery in a circuit?
Increase the amt. of
current flow ?
• Greater voltage battery or more
smaller batteries
• Shorter, thicker wire
• More conductive metal
• Light bulb with lower resistance
Decrease Resistance?
• Shorter length wire
• More conductive metal
• Thicker wires
Resistance &
Current
• High resistance = low current
• Low Resistance = high current
A
d
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V
o
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t
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e
Open or
closed
circuit ?
One bulb
• Single Resistance
• Full current
Two bulbs
• Double the resistance
• ½ the current
Three bulbs
• 3 times the resistance
• 1/3 the current
S
e
r
i
e
s
Series Circuit
Series or Parallel ?
Series Circuit
• Current only follows one path
• Amount of energy used by a circuit
must equal the energy supplied by
the battery
• Ex: cheap X-mas lights
Parallel Circuit
• Current has two or more possible
paths
• Each path is called a branch
• Same amt. of current must flow
out again
• Ex: your house (ask me to
explain!)
P
a
r
a
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Parallel
Parallel
AC or DC ?
• AC or alternating current –
direction of the current goes back
and forth
• In the US, most electrical systems
have a current that reverses 60
times per second
• Ex: your house
AC or DC ?
• DC or direct current – current that
flows in one direction
• Ex: a battery
Ground wire
• For safety
• Connected to the ground near
your house
• Ex: if your fridge has a short
circuit, then the electricity will flow
into the ground instead of through
YOU!
Nikola Tesla
• Physicist, Mechanical Engineer
• Many investigations w/ AC
• AC is easier to produce and
cheaper to use