1 science 90 physical science characteristics of electricity

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SCIENCE 90PHYSICAL SCIENCE

CHARACTERISTICS OF ELECTRICITY

• Science 90 Characteristics of Electricity Objectives• 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?• Static Current

• Random Organized

• Naturally occurring Manmade

• Hard to contain or Contained in

store 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 objectEg. 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

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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.

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.

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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 each other.

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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 Detection-The 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 ElectricityStatic 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.

• Radio, toaster, blow dryer, rechargeable battery in ipod

• 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

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 WattsThese 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

closed.

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Series Circuit

• Has only one pathway for electrons to flow

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.

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Parallel Circuit• There are 2 or more ways pathways for

electrons to flow.

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, ResistanceVoltage = 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

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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

– two main featuresa) contain two different metals (electrodes)

b) separated by a solution that conducts electricity (electrolyte)

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electrolyte

Positive electrode

Negative electrode

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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 terminal. This process repeats itself.

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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 upex// 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 easily conducted

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Three things effect resistance1. Length of the Wire2. Diameter of the Wire3. 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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Ohm’s LawOhm’s Law states that the current in a wire (I) is equal to the

voltage (V) divided by the resistance (R).

There are 3 EQUATIONS we can derive from this:

Current = Voltage Resistance

Voltage = Current x Resistance

Resistance = Voltage Current

Objective 6: Ohm’s Law

V

I R

Electrical Power Electrical Energy

P

V I

E

P T

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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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:

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 power52-60% Coal power

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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 kWStep 2 Multiply kW by the number of hours used

(0.2 kW)(150h) = 30 kWhStep 3 Multiply the kWh by the cost of electricity

(30kWh)($0.09) = $2.70

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QuestionsIf SaskPower charges 11 cents per kWh, calculate the following:

a) Using a toaster for 10h at 1000Wb) Using a desk lamp for 20h at 60Wc) Using a clock for 720h at 4Wd) Using a stove for 10h at 12000We) Using a dryer for 30h at 4600W

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14. Calculations

A. Electric EnergyThe 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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Examples:

1) If a blow dryer uses 350W and it is used for 19h in a month, how much will it cost if SaskPower charges 9 cents per kWh?

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2) If it costs a household $2.25 to operate their computer that uses 625W, how long did they use their computer for at 9 cents per kWh?

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3) How many watts does a machine use if it costs $1.10 to use the machine for 2h and it costs 9.5 cents per kWh?

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4) A grocery store is open from 9AM to 9PM seven days a week. If the store has twelve 120W light bulbs, how much would lighting cost in the month of June if SaskPower is charging 10 cents per kWh?

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C. Ohm’s LawOhm’s Law states that the current in a

wire (I) is equal to the voltage (V) divided by the resistance (R).

Current = Voltage Resistance

I = V R

Amp = Volts Ohms

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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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