Transcript Electricity - Science 90 / Biology 20

SCIENCE 90
PHYSICAL SCIENCE
CHARACTERISTICS OF
ELECTRICITY
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Science 90 Characteristics of Electricity Objectives
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A – Characteristics of Electricity
1 – Explore both static electricity and current electricity and explore methods of
charging.
2 – Understand static electric discharge, detection, transfer and technologies that
use this understanding.
3- Explore conductors, resistors and electrical circuits.
B – Voltage, Current and Resistance in Circuits
4 – Explore the difference between parallel and series circuits.
5 – Explore the role that current, voltage and resistance play in a circuit.
6 – Calculate circuit scenarios using Ohm’s Law and be able to problem solve using
electrical circuit drawings.
C – Electrical Energy
7 – Explore electrical loads used in day to day life and analyze energy efficiency.
8 – Make informed decisions about use of electrical energy and environmental
costs.
D – Energy Usage in Saskatchewan – Past / Present / Future
9 – Explore the transfer and conversion of energy into electricity in Saskatchewan.
10 – Explore various alternative energy sources for electricity production.
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Objective1.What is Electricity?
• Electricity is generated from the motion of
tiny charged atomic particles called
electrons!
• Protons = + charge
• Electrons = - charge
electron
neutron
proton
Electric Charge and Electrical Forces
• Electrons have a negative electrical charge.
• Protons have a positive electrical charge.
• These charges interact to create an electrical force.
– Like charges produce repulsive forces – so they
repel each other (e.g. electron and electron or proton
and proton repel each other).
– Unlike charges produce attractive forces – so they
attract each other (e.g. electron and proton attract
each other).
Electricity – Static or Current?
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Static
Random
Naturally occurring
Hard to contain or
store
Current
Organized
Manmade
Contained in
Batteries and
wires
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Static Electricity
– ELECTRIC FORCE = a build up of electric charge
– ELECTROSTATIC CHARGE = object acquires static
electricity when it has a build up of electrons
– Eg. Balloon rubbed on hair
– ELECTRIC DISCHARGE = is the removal of electric
charge from an object
Eg. rubbing your feet on the floor, or clothes with a
static cling, rubbing balloon on your head
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Theory of Electricity
- there are two types of charges, positive
and negative
– an object with no charge is said to be neutral
– when two types of matter are brought close
together, one may lose electrons to another.
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The 3 Laws of Electric Charges
1) Opposite charges attract each other
2) Like charges repel each other
3) Charged objects attract neutral objects
Bill Nye Static Electricity Demo
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Question – What happens when a charged object
is brought near water?
a) When water falls from a tap it is neutral
b) When a charged object is brought near water,
the electrons rearrange themselves in order
that there is an attraction.
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Objective 2 –
Electrostatic Discharge
• The charge on an ion is called an electrostatic
charge.
• An object becomes electrostatically charged by:
– Friction: Rubbing one object on another object
causes electrons to transfer from one object to the other,
– Conduction: a charged object contacts another object
which results in the transfer of electrons,
– Induction: a charged object comes close to another
object which causes the electrons to be rearranged in the
second object.
Charging by Induction
• When a positive charge is brought near
the bulb, all electrons from the leaves are
brought to the bulb. This causes both
leaves to become positive and they repel
each other.
• When a negative charge is brought near
the bulb, all electrons from the leaves are
pushed to the leaves. This causes both
leaves to become negative and they repel
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each other.
Charging by Conduction
• Same idea as induction, but the bulb is
actually contacted by the charged object,
so electrons are transferred. This means
that when the charged object is removed,
the leaves will remain open.
Grounding (-)
Grounding (+)
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Electrostatic DetectionThe Leaf Electroscope
• An electroscope has a metal bulb on the
top and two metal leaves along the bottom
of it that all have the ability to conduct
electricity easily.
Electroscope
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Technologies based on Static
Electric Knowledge:
Air filters – Electrically charged filter will
have dust particles attract to the filter
Fabric Softeners – Create coating of
neutralizing ions on fibres to reduce…
Plastic Wrap – Designed to easily become
negatively charged. Human body and food
easily become positively charged…
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• Car painting – Car metal is positively
charged. Paint is negatively charged.
Paint will be applied evenly and will stayed
bonded more permanently.
• Photocopiers – Uses static charging to
have the ink attract to the places where
letters , images need to go.
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Objective 3: Current Electricity
Static electricity = Electricity that normally is static (at rest)
Occasionally there is a discharge or transfer of electricity
but once the charges are passed, they do not continue to
move. The term used to describe this is “at rest”.
The 2 main methods of static electricity movement are:
-Induction
-Conduction
Current electricity = is when the charged particles continually
move through some Conductor in order to do some work.
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Radio, toaster, blow dryer, rechargeable battery in
ipod
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Some power source creates electrical current:
(batteries, generators, solar panels, etc…)
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Circuits and Switches
– if you connect one wire from a battery
terminal to a light bulb, nothing happens
until you connect a wire from the other end
– there must be a complete pathway for the
electrons to flow
– this is called an “ELECTRIC CIRCUIT”
– if electrons flow through, the circuit is
called closed
– if the electrons can not flow through, the
circuit is called open
– a switch makes one a closed circuit open
by disconnecting one of the wires (this
enables us to turn things on and off)
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Circuit Symbols
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Electrical Circuits
• Circuit = path for electrons to flow
• Switch – a control for stopping or starting the
flow of electrons through a circuit
• Load = anything that changes electrons in flow
into other forms of energy (light, motion, sound,
heat)
• Resistor = anything that hinders or lessens the
electrical flow through a circuit
• Conductor = anything which allows an electrical
flow through it
• Capacitor = a temporary energy storage (like
little batteries which ensure certain current rate)
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Switch Current (amps)
Source
(volts)
Load(watts)
Resistance, Voltage and Watts
These are the 3 factors that determine electrical circuit flow:
Voltage – Flow rate of electrons (electricity) through the wires
Wattage – The draw of Electricity from an appliance
Resistance – Anything which resists the flow of electricity
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4. Series and Parallel Circuits
– some Christmas lights shut off if one bulb
is removed
– this is known as a series circuit
– the removal of one bulb interrupts the flow
of electricity in the circuit
– most light do not work like this however
– these types of circuits are known as
parallel circuits
– electrons can flow in two or more
alternative paths
– if one bulb is removed, the path remains 24
closed.
Series Circuit
• Has only one pathway for electrons to flow
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What is a series circuit?
A series circuit is one which provides a single pathway for the current to flow. If
the circuit breaks, all devices using the circuit will fail.
Parallel Circuit
• There are 2 or more ways pathways for
electrons to flow.
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What is a parallel circuit?
A parallel circuit has multiple pathways for the current to flow. If the circuit is
broken the current may pass through other pathways and other devices will
continue to work.
Objective 5: Current, Voltage, Resistance
Voltage = flow rate from power source
= Volts (symbol = V)
Wattage = necessary amount of electricity to power a load
= Watts (symbol = w)
Resistance = any resistance to electrical flow (lost as heat, too small a
wire, too small a speaker etc…)
= Ohms (Symbol = R)
Current = flow of electricity
= Amps (symbol = I)
Power
= draw of electrical current from device
= Watts (Kilowatts)
Energy
= Measure of electricity usage by an appliance over a given
amount of time
= Kilowatt-hours
Detecting Current – Measuring
Current
– the ammeter is generally used to measure
current (the flow of electrons)
– the greater the number of electrons flowing
past the detector in a second, the greater the
current.
– The unity used to measure current is called
the “ampere” (amp) and the symbol used is
“A”
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Voltage of Cells and Batteries
– a cell is a device that converts
chemical energy into electrical energy
– two or more cells joined together are
called a battery
– a volt (V) is a unit used to measure
how much charge (quantity) is
delivered by a cell.
– The higher the voltage, the more
electrons leave the cell
– If two 1.5V batteries are used in a
piece of equipment, 3V are being
used
– A voltmeter is used to measure the
number of volts released by a battery
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Types of Cells and Batteries
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two main features
a) contain two different metals (electrodes)
b) separated by a solution that conducts
electricity (electrolyte)
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Negative electrode
Positive electrode
electrolyte
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How Do Batteries Work?
– Electrons begin at the positive electrode.
– The electrons then move across the
electrolyte to the negative electrode.
– The electrons gather at the negative
terminal and then are pushed out of there.
– The electrons provide energy to the device
being used and then are pulled back in by
the positive terminal.
– The electrons are then returned to the
positive electrode.
– For every electron that leaves the negative
terminal, one is returned to the positive
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terminal. This process repeats itself.
When do batteries Die?
• Batteries die when the paste of chemicals
dry out, or when the zinc layer becomes
used up.
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Types of Batteries
• Rechargeable Batteries
– generally use Ni and Cd (Nickel
and Cadmium)
– electrolyte is very caustic
(corrosive)
• Alkaline Batteries
– use Zn and MnO2
– useful for toys (last a long time)
• Car Battery
– use Pb and PbO
– provide current to starter, then a
generator (alternator) passes
current back to the battery to
recharge it.
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Resistance
– current can be affected by the type and
amount of wire that is used
– a resistor offers resistance to the flow of
charges
– the greater the resistance, the greater the
amount of energy is given up
ex// light bulb, toaster, etc.
– there is tungsten in the light bulb that does
not conduct very well
– therefore energy is given up to the bulb and
heat and light are produced
– if copper was used, light nor heat would be
produced because the electricity would be 37
easily conducted
 Three things effect resistance
1. Length of the Wire
2. Diameter of the Wire
3. Type of Wire
 The longer the wire, the more resistance.
 The thinner the wire, the more resistance.
 Copper would be a better conductor than a
pickle for example.
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A Light Bulb is an Example of a Resistor
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Objective 6: Ohm’s Law
Ohm’s Law
Ohm’s Law states that the current in a wire (I) is equal to the
voltage (V) divided by the resistance (R).
V
There are 3 EQUATIONS we
can derive from this:
I
R
Current = Voltage
Resistance
Voltage = Current x Resistance
Resistance = Voltage
Current
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Electrical Power
Electrical Energy
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Objective 7:
D. Electric Power
Electric power is a measure of the rate at which
electricity does work or provides energy. Watts (W)
are the unit that power is measured in.
Power = Voltage  Current
(P = V  I)
Watts = Volts  Amperes
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Examples:
1) The voltage in a computer is 120V and
the current is 20A. Calculate the
resistance and the power.
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2) The current in a MP3 player is 10A and
the resistance is 2Ω. With this information,
calculate the power being used.
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3) In a stereo, the energy being used is
25kWh. If it is used for 3h and the voltage
of the stereo is 110V, find the current.
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4) If the voltage in a machine is 30V and the
resistance is 2Ω, calculate the power
being used.
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EARTH DAY COMMERCIAL 20133min
Earth Hour CEO and Co-founder Andy Ridley's 2013
global launch keynote speech – YouTube12min
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:
http://myfootprint.org/en/your_carbon_footprint/
Go to the above website and calculate your effect on the environment:
To date Saskatchewan uses:
15-20% hydro power
3% Wind power
52-60% Coal power
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Wind Turbine Lab Discussion Questions:
1. Which basic design strategies proved to be the
most effective overall? ((Size, shape, weight,
angle, other?)
2. If you had the opportunity to redesign your
prototypes what would you change?
3. Was your hypothesis correct? Where there any
problems / weaknesses in how we tested your
prototypes?
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9. Electricity in the Home
– electrical devices can be grouped into
4 main categories
1) Light producing devices (lamps,
flashlights)
2) Heat producing devices (stoves, hair
dryers)
3) Mechanical producing devices
(vacuum, drill, saw)
4) Audio visual devices (TV, VCR,
radios)
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10. Measurement and Cost of
Electricity
– appliances use up energy
– in order to calculate the cost of
energy, we need to determine the
amount of energy used per second
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SaskPower charges 9 cents for each kWh of
electricity. Your TV consumes 200W and
you watch the TV 150h in a month. How
much will it cost to watch the TV for the
month?
Step 1  Convert the watts to kilowatts
200 W = 0.200 kW
Step 2  Multiply kW by the number of
hours used
(0.2 kW)(150h) = 30 kWh
Step 3  Multiply the kWh by the cost of
electricity
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(30kWh)($0.09) = $2.70
Questions
If SaskPower charges 11 cents per kWh,
calculate the following:
a) Using a toaster for 10h at 1000W
b) Using a desk lamp for 20h at 60W
c) Using a clock for 720h at 4W
d) Using a stove for 10h at 12000W
e) Using a dryer for 30h at 4600W
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14. Calculations
A. Electric Energy
The total amount of electric
energy used depends on the
total power used by all of the
electric appliances and the total
time they are used.
Energy = Power  Time
(E = P  t)
Kilowatt-hours = Kilowatts  Hours
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B. Cost of Electricity
How much a person pays for electricity depends
on two factors.
a) the price of electricity.
b) the amount of energy consumed.
The formula used for this is:
Total Cost = Price × Energy
T.C. = Price × E
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