Download Electricity

Electricity
Electric Charge
Positive and Negative Charge
• Atoms
– Protons (+) – Inside nucleus
– Neutron (0) – Inside nucleus
– Electron (-) – Outside Nucleus
• Static Electricity – excess electric charge
• Law of conservation of charge – charge
can be transferred but can not be created
of destroyed
Electric Charge
Positive and Negative Charge
• Opposite charges attract
• Like charges repel
• Electric fields surround every electric
charge, this exerts a force that causes
other electric charges to repel or attract.
Electric Charge
Insulator and Conductors
• Conductors
– Electrons are able to move
• Example – metal is a good conductor
• Insulators
– Electrons don’t move
• Example – plastic, rubber, wood and glass
Electric Charge
Charging Objects
• 2 material rub together they transfer
electrons
– One = positive
– The other = negative
– This is called “charging by contact”
Electric Charge
Charging Objects
• Charging by induction – rearrangement of
electrons on a neutral object caused by a
nearby object
• Lightning – large static discharge
• Thunder – hot air in lightning bolt path
expands rapidly, producing sound waves
• Ground – connecting an object to earth
with a good conductor
Detecting an electric charge
• Electroscope – detects electric charge
– No charge = straight down
– Charge touches rod…both ends negatively
charged = repel
Current and Voltage Difference
• Electric Current – net movement of electric
charges in a single direction.
– Electric Current – Measure in Amps
• 1 amp = 6,250 million billion electrons
flowing past a point every second
Current and Voltage Difference
• Voltage Difference – force that causes
electric charge to flow
– Measured in volts
Current and Voltage difference
• Circuit – closed path that an electric
current follows.
– If circuit is broken (open) current will not flow.
Batteries
• Purpose – provides the voltage difference
that is needed to keep electric current
flowing
Batteries
• Dry Cell
– Chemical reactions in
the paste transfer
electron to the zinc
container
Batteries
• Wet Cell Battery
– Made of different
metals of metallic
compounds in a
conducting solution.
Contain many wet
cells together
Battery
• Lead Acid Battery
– Series of six wet cells made up of lead and
lead dioxide plates in a sulfuric acid solution.
Resistance
• Resistance – tendency of material to
oppose the flow of electrons, changing
electrical energy into thermal energy and
light
Current in a simple circuit
• Contains a source of voltage difference
(battery) a device that has resistance (light
bulb) and conductors that connect the
device to the battery terminals.
Current in a simple circuit
• Ohm’s Law – current in a circuit equals the
voltage difference divided by the
resistance
• I = V/R
• Current = voltage difference / resistance
– Current – Amps
– Voltage Diff – Volts
– Resistance - Ohms
Series Circuits
• Current has only one loop to flow through
– Flash lights and some holiday lights
• Open circuit – when any part of the circuit
is disconnected no current flows through
the circuit
Parallel Circuits
• Contain two or more branches for current
to move through
• Advantages – when one branch is opened
(turn off a light) the current flows through
the other branches
Household Circuits
• Parallel Circuits
• In a house many appliances draw from the
same circuit. More appliances = more heat
– Fuse – current becomes too high small piece
of metal melts causes a break in the circuit.
– Circuit breaker – current gets to high, a small
piece of metal bends and opens the circuit,
can usually be reset by pushing it back to on
position.
Electrical Power
• Electrical Power – rate at which electricity
is converted into another form of energy
– Appliances with electric heating elements
(ovens, hair dryers, ovens) use more
electrical power that other appliances.
Electrical Power
• Calculating electrical power – depends on
the coltage difference and current
• Electrical Power = current(Amp)
X
Volatage diff. (volts)
Unit for power = watts
KW = 1,000 watts
Electrical Power
• Electrical Energy = kWh
• kWh = electrical power(kW)
X
Time(hrs)