Download - Chapter 20 Electricity. 20.1 Electric Charge and Static ElectricityElectricity 20.1 Electric Charge and Static Electricity

Chapter 20Chapter 20Electricity Electricity

20.1 Electric Charge and Static Electricity20.1 Electric Charge and Static Electricity ElectricityElectricity

20.1 Electric Charge and Static 20.1 Electric Charge and Static ElectricityElectricity


Electric ChargeElectric Charge

Electric energy is the energy associated Electric energy is the energy associated with electric charges. with electric charges.

Electric charge is a property that causes Electric charge is a property that causes subatomic articles to attract or repel each subatomic articles to attract or repel each other. other.

The atom is neutral because it has an The atom is neutral because it has an equal number of protons and electrons. equal number of protons and electrons.


An excess or shortage of electrons An excess or shortage of electrons produces a net electric charge. produces a net electric charge.

The SI unit of electric charge is the The SI unit of electric charge is the coulomb (C) which equivalent to 6.24×10coulomb (C) which equivalent to 6.24×101818 electrons.electrons.


Electric Forces Electric Forces

Like charges repel and opposite charges Like charges repel and opposite charges attract. attract.

The force of attraction or repulsion The force of attraction or repulsion between electrically charged objects is between electrically charged objects is electric force. electric force.


Coulomb discovered that electric forces Coulomb discovered that electric forces obey a law similar to the law of universal obey a law similar to the law of universal gravitation. gravitation.

The electric force between two objects is The electric force between two objects is directly proportional to the net charge on directly proportional to the net charge on each object and inversely proportional to each object and inversely proportional to the square of the distance between them. the square of the distance between them.

ElectricityElectricity


Electric FieldsElectric Fields

The effect an electric charge has on other The effect an electric charge has on other charges in the space around it is the charges in the space around it is the charge’s electric field. charge’s electric field.

The strength of an electric field depends The strength of an electric field depends on the amount of charge that produces the on the amount of charge that produces the field and on the distance from the charge. field and on the distance from the charge.


In figure 4, the lines representing the field In figure 4, the lines representing the field are closer together near the charge, where are closer together near the charge, where the field is stronger. the field is stronger.

An electric field exerts forces on any An electric field exerts forces on any charged object placed in the field. charged object placed in the field.

The force depends on the net charge in The force depends on the net charge in the object and on the strength and the object and on the strength and direction of the field at the object’s direction of the field at the object’s position.position.


Fields of Positive and Negative Fields of Positive and Negative ChargesCharges


Static Electricity and ChargingStatic Electricity and Charging

Static electricity is the study of the Static electricity is the study of the behavior of the electric charges, including behavior of the electric charges, including how charge is transferred between how charge is transferred between objects. objects.

Charge can be transferred by friction, by Charge can be transferred by friction, by contact, and by induction. contact, and by induction.


Whenever there is a charge transfer, the Whenever there is a charge transfer, the total charge is the same before and after total charge is the same before and after the transfer occurs. the transfer occurs.

The law of conservation of charge says The law of conservation of charge says the total charge in an isolated system is the total charge in an isolated system is constant. constant.


Charging by FrictionCharging by Friction

Rubbing a balloon through hair is an Rubbing a balloon through hair is an example of charging by friction. example of charging by friction.

Electrons move from the hair to the Electrons move from the hair to the balloon because atoms in rubber have a balloon because atoms in rubber have a greater attraction for electrons than atoms greater attraction for electrons than atoms in hair. in hair.


InductionInduction

Induction occurs when charge is Induction occurs when charge is transferred without contact between transferred without contact between materials. materials.


Static DischargeStatic Discharge

Static discharge occurs when a pathway Static discharge occurs when a pathway through which charges can move forms through which charges can move forms suddenly. suddenly.

Lightning is an example of static Lightning is an example of static discharge.discharge.

20.2 Electric Current and Ohm’s Law20.2 Electric Current and Ohm’s Law ElectricityElectricity

20.2 Electric Current and Ohm’s 20.2 Electric Current and Ohm’s LawLaw


Electric CurrentElectric Current

The continuous flow of electric charge is The continuous flow of electric charge is an electric current. an electric current.

The SI unit of electric current is the The SI unit of electric current is the ampere (A), or amp, which is equal to 1 ampere (A), or amp, which is equal to 1 coulomb per second. coulomb per second.

In direct current charge flows only in one In direct current charge flows only in one direction. direction.


In alternating current the flow of electric In alternating current the flow of electric charge regularly reverses its direction. charge regularly reverses its direction.


In direct current, electrons flow from the In direct current, electrons flow from the negative terminal of a battery to the negative terminal of a battery to the positive terminal. positive terminal.


However, scientists define current as the However, scientists define current as the direction in which positive charges would direction in which positive charges would flow. flow.


Conductor and InsulatorsConductor and Insulators

An electrical conductor is a material An electrical conductor is a material through which charge can flow easily. through which charge can flow easily.

Material through which charge cannot flow Material through which charge cannot flow easily is called an electrical insulator. easily is called an electrical insulator.


ResistanceResistance

Resistance is opposition to the flow of Resistance is opposition to the flow of charges in a material. charges in a material.

The SI unit of resistance is the ohm (Ω). The SI unit of resistance is the ohm (Ω). A material’s thickness, length, and A material’s thickness, length, and

temperature affect its resistance. temperature affect its resistance.


Resistance is lowered in a thicker wire Resistance is lowered in a thicker wire because more electrons can flow. because more electrons can flow.

Resistance is more in a longer wire Resistance is more in a longer wire because charges travel farther. because charges travel farther.

As temperature increases, resistance As temperature increases, resistance increases because electrons collide more increases because electrons collide more often. often.


A superconductor is a material that has A superconductor is a material that has almost zero resistance when it is cooled to almost zero resistance when it is cooled to low temperatures. low temperatures.

The best superconductor yet found must The best superconductor yet found must be cooled to about 138 K. be cooled to about 138 K.


VoltageVoltage

In order for charge to flow in a conducting In order for charge to flow in a conducting wire, the wire must be connected in a wire, the wire must be connected in a complete loop that includes a source of complete loop that includes a source of electrical energy. electrical energy.


Potential DifferencePotential Difference

Charges flow spontaneously from a higher Charges flow spontaneously from a higher to a lower potential energy. to a lower potential energy.

The potential energy of a charge depends The potential energy of a charge depends on its position in an electric field. on its position in an electric field.


Potential difference is the difference in Potential difference is the difference in electrical potential energy between two electrical potential energy between two places in an electric field. places in an electric field.

Potential difference is measured in joules Potential difference is measured in joules per coulomb, or volts. per coulomb, or volts.

Potential difference is also called voltage.Potential difference is also called voltage.


Voltage SourcesVoltage Sources

A source of voltage such as a battery does A source of voltage such as a battery does work to increase the potential energy of work to increase the potential energy of electric charges. electric charges.

Three common voltage sources are Three common voltage sources are batteries, solar cells, and generators. batteries, solar cells, and generators.

A battery is a device that converts A battery is a device that converts chemical energy to electrical energy. chemical energy to electrical energy.


Ohm’s LawOhm’s Law

The unit of resistance is the ohm. The unit of resistance is the ohm. Ohm discovered that voltage is not the Ohm discovered that voltage is not the

same everywhere in a circuit and same everywhere in a circuit and hypothesized that resistance reduces the hypothesized that resistance reduces the voltage. voltage.

He found a mathematical relationship He found a mathematical relationship between voltage, current, and resistance. between voltage, current, and resistance.


Ohm’s law states the voltage in a circuit Ohm’s law states the voltage in a circuit equals the product of the current and the equals the product of the current and the resistance, or resistance, or V=IR.V=IR.

When the current is in amps and resistance When the current is in amps and resistance is in ohms, the voltage is in volts. is in ohms, the voltage is in volts.

Increasing the voltage increases the current. Increasing the voltage increases the current. Keeping the same voltage and increasing the Keeping the same voltage and increasing the

resistance decreases the current. resistance decreases the current.

20.3 Electric Circuits20.3 Electric Circuits ElectricityElectricity

20.3 Electric Circuits20.3 Electric Circuits


Circuit DiagramsCircuit Diagrams

An electric circuit is a complete path An electric circuit is a complete path through which a charge can flow. through which a charge can flow.

Circuit diagrams use symbols to represent Circuit diagrams use symbols to represent parts of a circuit, including a source of parts of a circuit, including a source of electrical energy and devices that are run electrical energy and devices that are run by electrical energy. by electrical energy.

See figure 12.See figure 12.


Series CircuitsSeries Circuits

In a series circuit, the charge has only one In a series circuit, the charge has only one path through which it can flow. path through which it can flow.

If one element stops functioning in a series If one element stops functioning in a series circuit, none of the elements can operate. circuit, none of the elements can operate.

Adding bulbs to a series circuit increases Adding bulbs to a series circuit increases the resistance, decreases the current, and the resistance, decreases the current, and each bulb shines less brightly. each bulb shines less brightly.


Series CircuitSeries Circuit


Parallel CircuitsParallel Circuits

A parallel circuit is an electric circuit with A parallel circuit is an electric circuit with two or more paths through which charges two or more paths through which charges can flow. can flow.

If one element stops functioning in a If one element stops functioning in a parallel circuit, the rest of the elements still parallel circuit, the rest of the elements still operate.operate.


Parallel CircuitParallel Circuit


Power and Energy CalculationPower and Energy Calculation

Power is the rate of doing work. Power is the rate of doing work. The rate at which electrical energy is The rate at which electrical energy is

converted to another form of energy is converted to another form of energy is electric power. electric power.

The unit of electric power is the joule per The unit of electric power is the joule per second, or watt. second, or watt.


Power is often measured in kilowatts (kW). Power is often measured in kilowatts (kW). Electric power can be calculated by Electric power can be calculated by

multiplying voltage by current (multiplying voltage by current (P=IVP=IV). ). To find the electrical energy used by an To find the electrical energy used by an

appliance, multiply power by time (appliance, multiply power by time (E=PtE=Pt).). Unit is kilowatt hours (kWh).Unit is kilowatt hours (kWh).


Electrical SafetyElectrical Safety

Correct wiring, fuses, circuit breakers, Correct wiring, fuses, circuit breakers, insulation, and grounded plugs help make insulation, and grounded plugs help make electrical energy safe to use. electrical energy safe to use.

A fuse prevents current overload in a A fuse prevents current overload in a circuit. circuit.

A circuit breaker is a switch that opens A circuit breaker is a switch that opens when current in a circuit is too high. when current in a circuit is too high. The circuit breaker must be reset before The circuit breaker must be reset before

the circuit can be used again. the circuit can be used again.

20.4 Electronic Devices20.4 Electronic Devices ElectricityElectricity

20.4 Electronic Devices20.4 Electronic Devices


Electronic SignalsElectronic Signals

The science of using electric current to The science of using electric current to process or transmit information is electronics. process or transmit information is electronics.

An electronic signal is information sent as An electronic signal is information sent as patterns in the controlled flow of electrons patterns in the controlled flow of electrons through a circuit. through a circuit.

Electronics conveys information with Electronics conveys information with electrical patterns called analog and digital electrical patterns called analog and digital signals. signals.


Analog SignalsAnalog Signals

An analog signal is a smoothly varying An analog signal is a smoothly varying signal produced by continuously changing signal produced by continuously changing the voltage or current in a circuit. the voltage or current in a circuit.


Analog signal Analog signal changes continuously, changes continuously, has many voltage values, has many voltage values, resembles the pattern of the original resembles the pattern of the original

signal, signal, and is easily distorted.and is easily distorted.


Digital SignalsDigital Signals

A digital signal encodes information as s A digital signal encodes information as s string of 1’s and 0’s. string of 1’s and 0’s.

Digital signals are more reliable than Digital signals are more reliable than analog signals. analog signals.


Digital signal Digital signal changes abruptly, changes abruptly, has only two voltage values, has only two voltage values, does not resemble the original signal, does not resemble the original signal, and is not easily distorted. and is not easily distorted.

A DVD encodes digital signals as a series A DVD encodes digital signals as a series of pits on the DVD surface.of pits on the DVD surface.


Vacuum TubesVacuum Tubes

To create an electronic signal, the flow of To create an electronic signal, the flow of electrons must be controlled. electrons must be controlled.

A vacuum tube was used to control A vacuum tube was used to control electron flow in early electronic devices. electron flow in early electronic devices.


Vacuum tubes can Vacuum tubes can change alternating current into direct change alternating current into direct

current, current, increase the strength of a signal, or increase the strength of a signal, or turn a current on or off. turn a current on or off.


SemiconductorsSemiconductors

A semiconductor is a crystalline solid that A semiconductor is a crystalline solid that conducts current only under certain conducts current only under certain conditions. conditions.

Most semiconductors are made with Most semiconductors are made with silicon or germanium. silicon or germanium.


There are two types of semiconductorsThere are two types of semiconductors In n-type semiconductors, the current is In n-type semiconductors, the current is

a flow of electrons. a flow of electrons. In p-type semiconductors, it appears as In p-type semiconductors, it appears as

though positive charge flows. though positive charge flows.


Solid-State ComponentsSolid-State Components

Most modern electronic devices are Most modern electronic devices are controlled by solid-state components.controlled by solid-state components.


DiodesDiodes

A diode is a solid-state component that A diode is a solid-state component that combines an n-type and p-type combines an n-type and p-type semiconductors. semiconductors.

Because the current can be in only one Because the current can be in only one direction, a diode can change alternating direction, a diode can change alternating current to direct current.current to direct current.


TransistorsTransistors

A transistor is a solid-state component A transistor is a solid-state component with three layers of semiconductors.with three layers of semiconductors.

A transistor can be used as a switch A transistor can be used as a switch because the small current can turn current because the small current can turn current on or off.on or off.

Transistors can also be used as amplifiers.Transistors can also be used as amplifiers. Small voltage on one side produces Small voltage on one side produces

large voltage on the other side.large voltage on the other side.


Integrated CircuitsIntegrated Circuits

An integrated circuit is a thin slice of silicon An integrated circuit is a thin slice of silicon that contains many solid-state components.that contains many solid-state components.

Integrated circuits are also called chips or Integrated circuits are also called chips or microchips.microchips.

Integrated circuits are fast compared to Integrated circuits are fast compared to vacuum tubes. vacuum tubes. The current does not have to travel far to The current does not have to travel far to

get from point to point in the circuit.get from point to point in the circuit.

Download - Chapter 20 Electricity. 20.1 Electric Charge and Static ElectricityElectricity 20.1 Electric Charge and Static Electricity

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