Transcript Electricity Section 1 Electric Charge

FOPS: UNIT 4
Electricity
1
Mini Objectives
1. Describe how objects become electrically charged.
2. Explain how an electric charge affects other electric charges.
3. Distinguish between electric conductors and insulators.
4. Describe how electric discharges like lightening occur.
5. Relate voltage to the electrical energy carried by an electrical
current.
6. Describe a battery and how it produces an electric current.
7. Explain electrical resistance.
8. Explain how voltage, current, and resistance are related in an
electric current.
9. Investigate the difference between series and parallel circuits.
10. Determine the electric power used in a circuit.
11. Describe how to avoid dangerous electric shock.
Vocabulary
Electric Charge
Circuit
Ion
Voltage
Static Charge
Resistance
Electric Force
Ohm's Law
Electric Field
Series
Circuit
Insulator
Parallel
Circuit
Conductor
Electric Discharge Electric Power
Amperes
Electric Current
Introduction to Electricity VIDEO
What is electricity? Electricity is the flow of
electons or negative charges. It is both a basic
part of nature and one of our most widely
used forms of energy.
Electricity is actually a secondary energy
source, also referred to as an energy carrier.
That means that we get electricity from the
conversion of other sources of energy, such
as coal, nuclear, or solar energy. These are
called primary sources. The energy sources
we use to make electricity can be renewable
or non-renewable, but electricity itself is
neither renewable or nonrenewable.
How Americans use electricity
Electricity
• Protons and
Electrons have
positive and
negative charge
• Atom becomes +
if it loses
electrons, and – if
it gains electrons
then they are
called ions
Electrons Move in Solids
e- can move from atom to atom by
rubbing
– Ex. Rubbing a balloon on hair
» Hair holds e- more loosely, so
they go to the balloon, hair
becomes +, balloon becomes –
» Causes static charge- imbalance
of electric charge
QUESTION
Removing Static Electricity at
the Gas station…
• VIDEO
• Do you know what to do when
pumping gas?
Ions Move in Solution
• Movement of charge
can be caused by
movement of ions
• NaCl dissolved in
water Na+ and Clmove freely
• Play important role
in human body
(Nerve cell)
Movement of ions through a
nerve cell also called
physiology of a nerve
Electric Force
• Attractive or repulsive force that all charged
objects exert on each other
• “opposites attract and like repel”
• depends on distance and amount of charge
• Electric Fields- surrounds every electric
charge and exerts forces on other electric
charges
Insulators and Conductors
•
Insulator- e- can’t move freely
•
•
Ex. Plastic, wood, glass, rubber
Conductor- e- can move easily
•
•
Ex. Copper, gold, aluminum
Metals are best because e- are loosely
attached
Induced Charge
• Rubbing feet across
floor collects e- from
carpet, spread over
body as you go to
touch metal (door
knob), e- in your hand
move to the metal,
you feel an electric
discharge
Grounding
• Electrical discharge can cause damage and
injury.
i. Lightening
ii. Even small amt. can damage circuits
• One way to avoid this is to direct that current
into the ground called grounding.
Examples include: lightening rods, 3rd prong on a plug
Electric
Shock
Lightening Strikes!!
• VIDEO
• Do you know what to do in a storm?
• How do people die from lightening?
Van der graff
Generator
VIDEO
Electric Current
Vocabulary:
Electric current
Circuit
Voltage
Resistance
Flow of Charge
• Electric Current- flow of electric charge
– Liquids  ions
– Solids  electrons
Measured in amperes (A)
Andre-Marie Ampere
Model for Electric Circuit
• Circuit- closed conducting loop that
electric charge flows.
Series Circuits
• Series Circuit- has
only one path for
electric current to
follow.
• electrical devices are
connected along the
same current path.
Parallel Circuit
• A circuit that has more than
1 path for electric current to
flow.
• If one path is broken,
electrons continue to flow
through the other paths.
• resistance in each branch
can be different, depending
on the devices in the branch.
Schematics
Schematics of circuits are always shown in technical
manuals and other materials including textbooks. The
diagram below compares the pictorial diagram or real
world representation of the circuit you built in Exploration
1 with the schematic, or physics representation, of the
same circuit.
To be able to read or draw a schematic you will
need knowledge of what symbols are used to
represent the various elements in an electric circuit.
These symbols are fairly universal – a schematic
drawn in Asia will look the same as a schematic
drawn in the US, as long as the circuits are the
same. The table below shows some of the basic
schematic symbols used in this module.
29
Voltage
• voltage- of a battery is a measure of how
much electrical potential energy each
electron can gain.
• Measured in volts (V)
• As voltage increases, more electrical
potential energy is available
to be transformed into other
forms of energy.
Batteries
Batteries
• battery supplies
energy to an electric
circuit.
• alkaline battery two
terminals are
separated by a moist
paste.
Why do batteries die?
Battery Life
• Battery contains limited amt. of chemical.
• Reaction change chemicals into new
compounds.
• When chemicals used up battery is dead
Resistance
• measure of how difficult it is for electrons
to flow through a material.
• unit of resistance is the ohm (Ω).
• Insulators generally have much higher
resistance than conductors
Buildings Use Copper Wires
• Copper has low resistance and is one of
the best electric conductors.
• Less heat is produced as electric current
flows in copper wires, compared other
materials.
Resistance of Wires
• Depends on length, thickness, material.
• Increases – longer, thinner
Resistance at work
Light bulb Filaments
• filament is made of
wire so narrow that it
has a high resistance.
• electric current flows
in the filament, it
becomes hot enough
to emit light.
• made of tungsten
metal (high melting
pt)
Electric Circuits
Vocabulary
Ohm’s Law
Parallel Circuit
Series Circuit
Electric Power
Controlling the Current
Amount of current depends on:
– voltage supplied by the battery
– resistance of the conductor
Bucket height is like voltage 
higher up = more volts
Hose is like resistance 
longer and thinner = more resistance
Ohm’s Law
Voltage (v)= current (amps) x resistance (omh’s)
• If voltage in a circuit
increases the current
increases.
• When the resistance is
increased the circuit
decreases
Ohm’s Law example
A lightbulb is plugged into a wall outlet. If
the lightbulb has a resistance of 220Ω and
the current is 0.5 A, what is the voltage of
the outlet?
Current: I =0.5 A
Resistance: R= 220Ω
V = IR = (0.5 A) (220Ω) = 110V
Practice
1.
An electric iron plugged into a wall has a resistance of
24Ω. If the current in the iron is 5.0 A, what is the voltage
provided by the wall socket?
120 V
2.
What is the current in a flashlight bulb with a resistance
of 30 Ω if the voltage of the batteries is 3.0 V?
0.1 A
3.
What is the resistance of a bulb connected to a 110 V
wall outlet if the current in the bulb is 1.0 A?
110 Ω
Protecting Electric Circuits
• In a parallel circuit, current increases as
more devices are added  wire heats up.
• To keep the wire from becoming hot
enough to cause a fire, the circuits in
houses and other buildings have fuses or
circuit breakers.
Protecting Electric Circuits
Electric Power
Rate at which electrical energy is converted
into other forms of energy
• SI unit of power is the watt.
Power (watts) = Current (amps) x Voltage (volts)
Practice
A lightbulb is plugged into a 110 V wall outlet.
How much electric power does the lightbulb
use if the current in the bulb is 0.55 A?
Voltage: V = 110 V
Current: I = 0.55 A
P = IV = (0.55 A) (110 V) = 60 W
Practice
1.
The batteries in a portable CD player provide 6.0 V. If
the current in the CD player is 0.5 A, how much power
does the CD player use?
3.0 W
2.
What is the current in a toaster uses 1,100 W of power
when plugged into a 110 V wall outlet?
10 A
3.
An electric clothes dryer uses 4,400 W of electric
power. If the current in the dryer is 20.0 A, what is the
voltage?
220 V
Cost of Electric Power
• sell it in units of kilowatt-hours, amount of
electrical energy equal to using 1 kW of
power continuously for 1 h.
The End