• Explain briefly where electricity comes from.

S-66Students will investigate the properties of electricity and magnetism?

SPS10 Students will investigate the properties of electricity and magnetism.a. Investigate static electricity in terms of –friction, induction, conductionb. Explain the flow of electrons in terms of

-alternating and direct current-the relationship among voltage, resistance, and current-simple series and parallel circuits

Chapter 20

Electricity

What produces a net electric charge?What determines whether an electric force is attractive or repulsive?What determines the strength of an electric field.What are three ways in which charge is transferred.How does static discharge occur?

20.1 Electric Charge and Static Electricity

• Electric Charge – a property that causes protons and electrons to attract or repel each other– Two types– Positive - protons – Negative – electrons– An excess or shortage of electrons

causes atoms to be charged– That causes objects to be charged

20.1 Charge and StaticsWhat produces a net electric charge?

• Electric Force – force of attraction or repulsion between

electrically charged objects– Like charges repel

(positve-positive, or negative-negative)

– Opposite charges attract (negative-positive)

20.1 Charge and StaticsWhat determines whether an electric force is attractive or repulsive?

• Electric Field – the space around a charged particle where it will push or pull another charge– Depends on– Amount of charge– Distance from the charge

• Drops off rapidly (square of the distance)

20.1 Charge and StaticsWhat determines the strength of an electric field?

• Static Electricity – charges that are not moving

• Law of conservation of charge – the total amount of charge stays the same – Remember that charge is

caused by protons and electrons

20.1 Charge and StaticsWhat are the three ways in which charge is transfered?

• There are three ways that charge is transffered– Friction

• Two uncharge objects rub against each other• Electrons are pulled off one object and

placed on the other

– Contact• A charged object comes in contact with an

uncharged object• The charged object loses charge until they

both have the same charge

20.1 Charge and StaticsWhat are the three ways in which charge is transfered?

• There are three ways that charge is transffered– Induction

• Electrons in an object are attracted or repelled

by a charge• This causes a

temporary charge in a neutral object

20.1 Charge and StaticsWhat are the three ways in which charge is transfered?

• What are the two types of charges?• What are the two basic charged

particles?• How does a

charge form?

S-67Students will investigate the properties of electricity and magnetism?

• Electrons will flow if there is a conducting pathway– Static discharge when a pathway

between charged objects is formed

• Shocking yourself on a doorknob

• Lighting bolt

20.1 Charge and StaticsHow does static discharge occur?

What are the two types of current?What are some examples of conductors and insulators?What factors affect electrical resistance?What causes and electric current?How are voltage, current, and resistance related?

20.2 Electric Current and Ohm’s Law

• Electric Current – the flow of charge– Two types– Direct Current

• Flows in only one direction• Electricity from batteries

– Alternating current• Changes direction in a regular pattern• Has frequency (usually 60 Hz)• Household electricity

20.2 Current and Ohm’s LawWhat are the two types of current?

• Electrical conductor – material that charge flows through easily– Metals– Graphite– Salt solutions

• Electrical insulator – material that charge does not flow through easily– Plastics– Rubber

20.2 Current and Ohm’s LawWhat are some examples of conductors and insulators?

• Resistance – opposition to the flow of charge– Resistors use up the energy in electricity– Measured in Ohm ()– Three factors affect resistance

• Thickness – thicker objects have less resistance

• Lenth – longer objects have more resistance• Temperature – resistance increases with

temperature

20.2 Current and Ohm’s LawWhat factors affect electrical resistance?

• Voltage (Potential Difference) – difference in potential energy between two points– Units are volts (V)– Produced by sources of electric energy– A potential difference placed across a

loop of conductor will result in a current– Current is measured in Amperes – or

Amps (A)

20.2 Current and Ohm’s LawWhat causes an electric current?

• Ohm’s Law – current is equal to potential divided by resistance

– V = potential difference in volts (V)– I = current in amps (A)– R = resistance in Ohm’s ()

20.2 Current and Ohm’s LawHow are voltage, current, and resistance related?

V=IR

• What is the potential difference that would allow a 7 A current to flow through a 14 toaster?

– Fill in the equation– Answer

20.2 Current and Ohm’s LawHow are voltage, current, and resistance related?

V=IRV=(7A)(14)V=98V

• How much current would flow through a 96 light bulb when it is plugged into a 120 V source?

– Fill in the equation– Answer

20.2 Current and Ohm’s LawHow are voltage, current, and resistance related?

V=IR120V=I(96)I=1.25A

• A toaster is plugged into a 120 V wall outlet. How much current will it draw if it is a 47 resistor?

S-68How are voltage, current, and resistance related?

• What three factors determine the resistance of an object?

• How does resistance change as each factor changes?

S-69What factors affect electrical resistance?

What is included in a circuit diagram?How do series and parallel circuits differ?How do you calculate electric power?

20.3 Electric Circuits

• Electric Circuit – complete pathway– Circuit diagram – show the path and

devices in the pathway– Common symbols are

• Battery • Battery of cells• Resistor• Light bulb• Switch

20.3 Electric CircuitsWhat is included in a circuit diagram?

• Series Circuit– Has only one pathway for current– If one device is disconnected they all

stop working

• Parallel Circuit– Has more than one pathway for current– Devices don’t affect other devices– Household circuits are parallel

20.3 Electric CircuitsHow do series and parallel circuits differ?

• Power is equal to voltage multiplied by current

– P = power in watts (W)– I = current in amps (A)– V = potential difference in volts (V)

20.2 Current and Ohm’s LawHow do you calculate electric power?

P=IV

• An electric oven is connected to a 240 V line, and it uses 34 amps of current. What is the power used by the oven?

– Fill in the equation– Answer

20.2 Current and Ohm’s LawHow do you calculate power?

P=IVP=(34A)(240)P=8160W

• How much power would a hair dryer use if it draws 15A of current when plugged into a 120V wall socket?

• Hair dryer –boring• Powerful tank - cool

S-70How do you calculate power?