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ElectricityFOPS: UNIT 4

Mini Objectives1. 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.

VocabularyElectric ChargeIonStatic ChargeElectric ForceElectric Field InsulatorConductorElectric DischargeElectric Current

CircuitVoltageResistanceOhm's LawSeries CircuitParallel CircuitElectric PowerAmperes

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 Cl- move 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 Voltage

Circuit 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.

SchematicsSchematics 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.

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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.

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 Series Circuit

Parallel 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 AResistance: 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?

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?

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?

120 V

0.1 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 VCurrent: 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?

2. What is the current in a toaster uses 1,100 W of power when plugged into a 110 V wall outlet?

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?

3.0 W

10 A

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