Transcript ELECTRICITY NOTES

ELECTRICITY NOTES
ELECTRICITY
• ELECTRICITY: form of energy that
occurs when electrons move from
place to place
• Electricity can form whenever (e-)
electrons are gained or lost
• All substances are made up of ATOMS
which contain electrically charged
particles called PROTONS and
ELECTRONS
• PROTONS have a positive (+) charge
• ELECTRONS have a negative (-) charge
• How can neutral substances become
electrically charged?
– When a neutral object slides past another
object and picks up extra e– An object with more protons has a +
charge
– An object with more electrons has a charge
STATIC ELECTRICITY
• STATIC ELECTRICITY is a buildup of
electrons on an object
• CONDUCTORS: allow electrons to pass
through easily
– Examples: METALS, WATER
• INSULATORS: do NOT allow electrons to
pass through easily
– Examples: NONMETALS
When 2 objects are rubbed together
they become CHARGED
Objects with like charges REPEL
Objects with opposite charges ATTRACT
INDUCTION
• INDUCTION occurs when a neutral
object becomes charged by holding a
charged object close to it (NOT
touching)
How is Earth’s Surface Charged
by Induction?
An ELECTROSCOPE is a devise that
detects electric charge. A metal knob
is connected to 2 metal leaves. When
a charged object touches the knob,
the leaves SEPARATE
GROUNDING
• GROUNDING: touching a charged
object to the ground to remove extra
charges
Moving charges produce CURRENT
ELECTRICITY which flows along a path
called a CIRCUIT.
Current that only flows in one direction is
called DIRECT CURRENT (battery
powered).
Current that reverse its direction
constantly is called ALTERNATING
CURRENT (AC) (power company)
ELECTRIC CURRENT
(I)
• THE FLOW OF e- (how many are flowing
through each second)
• Units: AMPERES (A)
1 AMPERE = 6.25 X1018 e- EACH SECOND
ELECTRIC CELL
• An ELECTRIC CELL is a devise that converts
chemical energy into electrical energy. 2 or
more electric cells combined make up a
BATTERY.
• An electric cell contains two different
substances called ELECTRODES. The
electrodes are places in a conducting
mixture called an ELECTROLYTE. Chemical
reactions take place between the
ELECTRODES and the ELECTROLYTE.
• Wet Cell: a battery with a liquid
electrolyte…acid (car battery)
• Dry Cell: battery whose electrolyte is a
paste instead of a liquid (AA, C, D
batteries, etc)
• Anode: - end of battery where e- leave
the battery
• Cathode: + end of battery where ereturn to the battery
• VOLTAGE (V) also called POTENTIAL
DIFFERENCE. It is the difference
between one end of the power source
and the other end.
– Units: VOLTS (V)
RESISTANCE (R)
• RESISTANCE is the opposition to
electron flow. Conductors have LOW
resistance. Insulators have HIGH
resistance.
– Units: Ohms Ω
• Resistance depends on TEMPERATURE,
DIAMETER, LENGTH, METVAL vs.
NONMETAL
Ohms Law
V = IR
voltage = current x resistance
The filament in a light bulb uses a current
of 0.5 A when the voltage is 120V.
What is its resistance?
Circuits
• A path for electrons to travel through is
called an ELECTRIC CIRCUIT
• If an electron can flow in a complete
path, the circuit is A CLOSED CIRCUIT
• If a connection is broken along the
circuit, it becomes AN OPEN CIRCUIT
• Switch: A DEVICE THAT CAN OPEN A
CIRCUIT
Simple Circuits
• Made up of
1. power source (battery, generator)
2. conductor (wire)
3. load (bulb, resistor, motor)
SAFETY DEVICES on CIRCUITS that
PREVENT FIRES
1. CIRCUIT BREAKER: switch that opens
when current is too high
2. FUSES: a switch that melts when
current is to high
TYPES OF CIRCUITS
• A SERIES CIRCUIT only has 1 path for
electrons
• A PARALLEL CIRCUIT has more than
one path for electrons.
Short Circuits
• Short Circuit: when uninsulated wires
touch and the e- take a shorter path;
can overheat and cause a fire
Electric Power
The amount of electrical energy used
each second is called ELECTRIC
POWER , RATE AT WHICH ENERGY IS
CONVERTED
Units: Watts (w) or Kilowatts (kW)
Formula: P = VI
Power = Volts x Current
How much electrical power is used by a
TV that uses a current of 0.5A when
connected to a voltage of 120V?
Electrical Energy Power
E = Pt
energy = power x time
A hairdryer with a power rating of
1500W is used for 120 seconds. How
much electrical energy does it use?
Kilowatt-hour
• The unit for energy used by the power
company