Download - Chapter 20: Electricity 20.1 Electric Charge and Static Electricity

Chapter 20: Chapter 20: ElectricityElectricity

20.1 Electric Charge 20.1 Electric Charge and Static Electricityand Static Electricity

Electric chargeElectric charge is a property is a property that causes subatomic particles that causes subatomic particles such as protons and electrons to such as protons and electrons to attract or repel each other. attract or repel each other.

• Protons have a positive Protons have a positive charge.charge.

• Electrons have a negative Electrons have a negative charge.charge.

Electric Charge

In an atom, a cloud of negatively charged In an atom, a cloud of negatively charged electrons surrounds the positively charged electrons surrounds the positively charged nucleus. The atom is neutral because it nucleus. The atom is neutral because it has equal numbers of positive and has equal numbers of positive and negative charges.negative charges.

• If an atom gains electrons, it becomes If an atom gains electrons, it becomes a negatively charged ion. a negatively charged ion.

• If an atom loses electrons, it becomes If an atom loses electrons, it becomes a positively charged ion.a positively charged ion.

Electric Charge

The SI unit of electric charge is the The SI unit of electric charge is the coulombcoulomb (C). (C).

• It takes about 6.24 × It takes about 6.24 × 10101818 electrons to produce a single electrons to produce a single coulomb. coulomb.

Electric Charge

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

• The electric force between two The electric force between two objects is directly proportional to objects is directly proportional to the net charge on each object.the net charge on each object.

• The electric force is inversely The electric force is inversely proportional to the square of the proportional to the square of the distance between the objects. distance between the objects.

Electric Forces

Doubling the net charge on one Doubling the net charge on one object doubles the electric force. object doubles the electric force.

Doubling the distance between the Doubling the distance between the objects decreases the electric force objects decreases the electric force to one fourth the original force.to one fourth the original force.

Inside an atom, electric forces are Inside an atom, electric forces are much stronger than gravitational much stronger than gravitational forces. forces.

Electric Forces

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

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

• The direction of each field line shows the The direction of each field line shows the direction of the force on a positive charge.direction of the force on a positive charge.

Electric Fields

A.A. The electric field around a positive The electric field around a positive charge points outward. charge points outward.

B.B. The electric field around a negative The electric field around a negative charge points inward.charge points inward.

Electric Fields

Field of a positive charge Field of a negative charge

Static electricityStatic electricity is the study of the is the study of the behavior of electric charges. behavior of electric charges.

According to the According to the law of law of conservation of chargeconservation of charge, , the total the total charge in an isolated system is charge in an isolated system is constant. When there is a charge constant. When there is a charge transfer, the total charge is the same transfer, the total charge is the same before and after the transfer occurs.before and after the transfer occurs.

Static Electricity and Charging

Charging by FrictionCharging by Friction

Rubbing a balloon on your hair causes Rubbing a balloon on your hair causes charging by friction.charging by friction.

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

• The balloon picks up a net negative The balloon picks up a net negative charge.charge.

• Your hair loses electrons and becomes Your hair loses electrons and becomes positively charged.positively charged.


Charging by ContactCharging by Contact

A Van de Graaff generator builds a A Van de Graaff generator builds a charge on a metal sphere. charge on a metal sphere. Touching the sphere transfers Touching the sphere transfers charge by contact. charge by contact.

The sphere is still charged, but its The sphere is still charged, but its net charge is reduced.net charge is reduced.


Charging by InductionCharging by Induction

Walking on a carpet builds a negative Walking on a carpet builds a negative charge on your body. The negative charge on your body. The negative charge in your hand repels electrons in charge in your hand repels electrons in a metal doorknob.a metal doorknob.

The doorknob is still neutral, but charge The doorknob is still neutral, but charge has moved within it. This is has moved within it. This is inductioninduction, , a transfer of charge without contact a transfer of charge without contact between materials.between materials.


Static Discharge

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

Lightning is a more dramatic discharge.Lightning is a more dramatic discharge.• Charge can build up in a storm cloud from Charge can build up in a storm cloud from

friction between moving air masses. friction between moving air masses. • Negative charge in the lower part of the cloud Negative charge in the lower part of the cloud

induces a positive charge in the ground induces a positive charge in the ground below the cloud. below the cloud.

• As the charge in the cloud increases, the As the charge in the cloud increases, the force of attraction between charges in the force of attraction between charges in the cloud and charges in the ground increases.cloud and charges in the ground increases.

• Eventually the air becomes charged, forming Eventually the air becomes charged, forming a pathway for electrons to travel from the a pathway for electrons to travel from the cloud to the ground. cloud to the ground.

Static Discharge

Assessment Questions

1.1. Which of the following would double Which of the following would double the electric force between two charged the electric force between two charged objects? objects?

a.a. doubling the mass of the objectsdoubling the mass of the objects

b.b. doubling the net charge of both doubling the net charge of both objectsobjects

c.c. doubling the net charge of one of the doubling the net charge of one of the objectsobjects

d.d. cutting the distance between the cutting the distance between the objects in halfobjects in half


2.2. The attractive or repulsive effect an The attractive or repulsive effect an electric charge has on other electric charge has on other charges in the space around it is charges in the space around it is the charge’s the charge’s a.a. electric force.electric force.b.b. electric field.electric field.c.c. static electricity.static electricity.d.d. static discharge.static discharge.

Assessment Questions3.3. An object becomes charged by induction An object becomes charged by induction

when there is a when there is a

a.a. transfer of electrons, as the object rubs transfer of electrons, as the object rubs against another object.against another object.

b.b. transfer of charge, as it contacts another transfer of charge, as it contacts another charged object.charged object.

c.c. transfer of charge by motion of electrons transfer of charge by motion of electrons within the object.within the object.

d.d. a sudden movement of electric charge a sudden movement of electric charge from another object.from another object.

Chapter 20: Chapter 20: ElectricityElectricity

20.2 Electric Current 20.2 Electric Current and Ohm’s Lawand Ohm’s Law

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

• Charge flows only in one direction in Charge flows only in one direction in direct currentdirect current (DC). A flashlight and (DC). A flashlight and most other battery-operated devices use most other battery-operated devices use direct current. direct current.

• Alternating currentAlternating current (AC) is a flow of (AC) is a flow of electric charge that regularly reverses its electric charge that regularly reverses its direction. direction.

Electric Current

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

Even though electrons flow in Even though electrons flow in an electric current, scientists an electric current, scientists define current as the direction define current as the direction in which positive charges would in which positive charges would flow. flow.

Electric Current

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

An An electrical insulatorelectrical insulator is a is a material through which charge material through which charge cannot flow easily.cannot flow easily.

Conductors and Insulators

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

• As electrons move through a As electrons move through a conducting wire, they collide with conducting wire, they collide with electrons and ions. These collisions electrons and ions. These collisions convert some kinetic energy into convert some kinetic energy into thermal energy, and the current is thermal energy, and the current is reduced. reduced.

• The SI unit of resistance is the The SI unit of resistance is the ohmohm..

Resistance

Resistance is greater in a longer wire Resistance is greater in a longer wire because the charges travel farther. because the charges travel farther. As temperature increases, a metal’s As temperature increases, a metal’s resistance increases because resistance increases because electrons collide more often.electrons collide more often.

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

Resistance

Potential DifferencePotential Difference

Electric charges flow from a higher to a Electric charges flow from a higher to a lower potential energy.lower potential energy.

• Potential differencePotential difference is the difference in 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 Potential difference is measured in joules per coulomb, or volts. Because it joules per coulomb, or volts. Because it is measured in volts, potential difference is measured in volts, potential difference is also called is also called voltagevoltage..

Voltage SourcesVoltage Sources

A source of voltage does work to A source of voltage does work to increase the potential energy of increase the potential energy of electric charges. Three common electric charges. Three common voltage sources are batteries, solar voltage sources are batteries, solar cells, and generators.cells, and generators.

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

Voltage

According to According to Ohm’s law, Ohm’s law, the voltage (the voltage (VV) ) in a circuit equals the product of the in a circuit equals the product of the current (current (II) and the resistance () and the resistance (RR).).

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

Ohm’s Law

What is the voltage if the What is the voltage if the resistance is 3 ohms and the resistance is 3 ohms and the current is 3 amps?current is 3 amps?

Ohm’s Law

Resistance ExampleResistance Example

The headlights of a typical car are The headlights of a typical car are powered by a 12 V battery. What is powered by a 12 V battery. What is the resistance of the headlights if they the resistance of the headlights if they draw 3.0 A of current when turned draw 3.0 A of current when turned on?on?

Resistance PracticeResistance Practice1.1. Find resistance if a portable Find resistance if a portable

lantern uses 24 V power lantern uses 24 V power supply and draws a current of supply and draws a current of 0.8 A0.8 A

2.2. If the current is 0.5 A and the If the current is 0.5 A and the resistance is 12 resistance is 12 ΩΩ, what is , what is the voltage?the voltage?

Resistance PracticeResistance Practice

I (amps)I (amps) V (volts)V (volts) R (ohms)R (ohms)

1212 7575

1515 240240

5.55.5 2020

66 2525

55 110110


1.1. Which of the following materials is Which of the following materials is a good conductor of electric a good conductor of electric current? current?

a.a. woodwood

b.b. glassglass

c.c. airair

d.d. ironiron


2.2. If a piece of wire has a certain If a piece of wire has a certain resistance, which wire made of the resistance, which wire made of the same material will have a lower same material will have a lower resistance? resistance? a.a. a hotter wirea hotter wireb.b. a thicker wirea thicker wirec.c. a longer wirea longer wired.d. a thinner wirea thinner wire


3.3. What does the voltage between two What does the voltage between two points in an electric field represent? points in an electric field represent?

a.a. the total kinetic energythe total kinetic energy

b.b. the difference in mechanical energythe difference in mechanical energy

c.c. the difference in potential energythe difference in potential energy

d.d. the electrical energy the electrical energy


4.4. A 9-volt battery drives an electric A 9-volt battery drives an electric current through a circuit with 4-ohm current through a circuit with 4-ohm resistance. What is the electric current resistance. What is the electric current running through the circuit? running through the circuit?

a.a. 0.44 A0.44 A

b.b. 2.25 A2.25 A

c.c. 5 A5 A

d.d. 36 A36 A


5.5. The two types of electric current The two types of electric current are direct current and indirect are direct current and indirect current.current.

TrueTrueFalseFalse

Chapter 20 Chapter 20 ElectricityElectricity

20.3 Electric 20.3 Electric CircuitsCircuits

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

• A circuit diagram shows one or more A circuit diagram shows one or more complete paths in which charge can complete paths in which charge can flow. flow.

• Arrows show the direction of current, Arrows show the direction of current, from positive to negative. The direction from positive to negative. The direction of current is defined as the direction in of current is defined as the direction in which positive charges would flow, but which positive charges would flow, but electrons flow in the opposite direction.electrons flow in the opposite direction.

Circuit Diagrams

SwitchesSwitches show places where the circuit show places where the circuit can be opened. can be opened.

• If a switch is open, the circuit is not If a switch is open, the circuit is not a complete loop, and current stops. a complete loop, and current stops. This is called an This is called an open circuitopen circuit. .

• If the switch is closed, the circuit is If the switch is closed, the circuit is complete, and charge can flow. This complete, and charge can flow. This is called a is called a closed circuitclosed circuit..

Circuit Diagrams

Circuit ComponentsCircuit Components

A - batteryA - battery C - light bulbC - light bulb

B - switchB - switch D - resistorD - resistor

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

• If one bulb burns out in a series If one bulb burns out in a series circuit, it becomes an open circuit. circuit, it becomes an open circuit.

• The bulbs in a circuit are a source of The bulbs in a circuit are a source of resistance. Adding bulbs to a series resistance. Adding bulbs to a series circuit increases the resistance. The circuit increases the resistance. The current decreases, and each bulb current decreases, and each bulb shines less brightly.shines less brightly.

Series Circuits

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

• If one bulb in a parallel circuit burns If one bulb in a parallel circuit burns out, charge still flows along the other out, charge still flows along the other path, and the other bulb stays lit.path, and the other bulb stays lit.

• In a home, electric circuits are wired In a home, electric circuits are wired in parallel so they can operate in parallel so they can operate independently. independently.

Parallel Circuits

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. Recall that power is the Recall that power is the rate of doing work.rate of doing work.

The unit of electric power is the joule per The unit of electric power is the joule per second, or watt (W). Power often is second, or watt (W). Power often is measured in thousands of watts, or measured in thousands of watts, or kilowatts (kW).kilowatts (kW).

Power and Energy Calculations

Calculating Electric PowerCalculating Electric Power

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


1.1. A clothes dryer uses about 27 A clothes dryer uses about 27 amps of current from a 240-volt amps of current from a 240-volt line. How much power does it line. How much power does it use? use?

Answer: Answer:


2.2. A camcorder has a power A camcorder has a power rating of 2.3 watts. If the output rating of 2.3 watts. If the output voltage from its battery is 7.2 voltage from its battery is 7.2 volts, what current does it use? volts, what current does it use?

Answer: Answer:


3.3. A power tool uses about 12 A power tool uses about 12 amps of current and has a power amps of current and has a power rating of 1440 watts. What rating of 1440 watts. What voltage does the tool require? voltage does the tool require?

Answer: Answer:


4.4. When a hairdryer is plugged into When a hairdryer is plugged into a 120 V outlet, it has 9.1 A current in a 120 V outlet, it has 9.1 A current in it. What is the power rating?it. What is the power rating?

Electric Power PracticeElectric Power Practice1.1. A heater requires 29 A of 120 V A heater requires 29 A of 120 V

current, find powercurrent, find power

2.2. A TV has a power rating of 320 W, A TV has a power rating of 320 W, how much current is there across how much current is there across 120 V?120 V?

An appliance's power rating lets you An appliance's power rating lets you know how much power it uses under know how much power it uses under normal conditions. normal conditions.

Find the electrical energy used by an Find the electrical energy used by an appliance by multiplying power by time. appliance by multiplying power by time.


Home SafetyHome Safety

A A fusefuse prevents current overload in a prevents current overload in a circuit. A wire in the center of the fuse circuit. A wire in the center of the fuse melts if too much current passes melts if too much current passes through it.through it.

A A circuit breakercircuit breaker is a switch that is a switch that opens when current in a circuit is too opens when current in a circuit is too high. The circuit breaker must be reset high. The circuit breaker must be reset before the circuit can be used again.before the circuit can be used again.

Electrical Safety

Insulation also prevents short circuits. Insulation also prevents short circuits.

A three-prong plug can prevent shocks A three-prong plug can prevent shocks caused by short circuits. If a short circuit caused by short circuits. If a short circuit develops, the current takes an easier develops, the current takes an easier path to ground through the grounding path to ground through the grounding wire. wire.

The transfer of excess charge through a The transfer of excess charge through a conductor to Earth is called conductor to Earth is called groundinggrounding..

Electrical Safety

A A ground-fault circuit interrupterground-fault circuit interrupter (GFCI) is an electrical safety outlet. (GFCI) is an electrical safety outlet. It monitors current flowing to and It monitors current flowing to and from an outlet or appliance. from an outlet or appliance.

If these two currents are not equal, If these two currents are not equal, it means current is escaping. it means current is escaping.

The GFCI opens the circuit to The GFCI opens the circuit to prevent serious electric shocks.prevent serious electric shocks.

Electrical Safety


1.1. A number of light bulbs are connected A number of light bulbs are connected to an energy source in a series circuit. to an energy source in a series circuit. What will happen to the other bulbs if What will happen to the other bulbs if one of the bulbs burns out? one of the bulbs burns out?

a.a. Nothing will happen.Nothing will happen.

b.b. They will be brighter.They will be brighter.

c.c. They will be dimmer.They will be dimmer.

d.d. They will turn off.They will turn off.


2.2. A pair of 15-watt computer speakers A pair of 15-watt computer speakers are connected to a 12-volt power are connected to a 12-volt power supply. What is the electric current supply. What is the electric current running through the speakers? running through the speakers? a.a. 0.8 A0.8 Ab.b. 1.25 A1.25 Ac.c. 12.5 A12.5 Ad.d. 180 A180 A


3.3. A ground-fault circuit interrupter is A ground-fault circuit interrupter is a switch that opens to prevent a switch that opens to prevent overheating when the current in a overheating when the current in a circuit is too high. circuit is too high.

TrueTrueFalseFalse

Chapter 20 Chapter 20 ElectricityElectricity

20.4 Electronic 20.4 Electronic DevicesDevices

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

• Information is carried by an Information is carried by an electronic electronic signalsignal, , patterns in the controlled flow of patterns in the controlled flow of electrons through a circuit.electrons through a circuit.

Electronic Signals

Analog SignalsAnalog Signals

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

Information is encoded in the Information is encoded in the strength or frequency of the analog strength or frequency of the analog signal.signal.

Electronic Signals

Digital SignalsDigital Signals

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

When the current is off, it When the current is off, it represents a “0.” When the current represents a “0.” When the current is on, it represents a “1.” is on, it represents a “1.”

Electronic Signals

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

Vacuum tubes have many useful Vacuum tubes have many useful features, but some types burn out features, but some types burn out frequently and need to be frequently and need to be replaced. They are also much too replaced. They are also much too large for use in small electronic large for use in small electronic devices.devices.

Vacuum Tubes

One useful type of vacuum tube is a One useful type of vacuum tube is a cathode-ray tubecathode-ray tube (CRT). (CRT).

• Three metal plates in the CRT emit Three metal plates in the CRT emit electron beams. electron beams.

• The electrons strike a glass surface on The electrons strike a glass surface on the other end of the tube.the other end of the tube.

• The glass is coated with phosphors The glass is coated with phosphors that glow red, green, or blue in that glow red, green, or blue in response to the electron beams. response to the electron beams.

Vacuum Tubes

A A semiconductor semiconductor is a crystalline solid that 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. In pure form, silicon or germanium. In pure form, these elements are poor conductors.these elements are poor conductors.

Semiconductors

A A p-typep-type semiconductor can be made semiconductor can be made by adding a trace amount of boron to by adding a trace amount of boron to silicon. Spaces called holes occur at silicon. Spaces called holes occur at each boron atom. The holes are each boron atom. The holes are positively charged. positively charged.

An An n-typen-type semiconductor can be semiconductor can be made by adding phosphorus to made by adding phosphorus to silicon. Phosphorus atoms provide silicon. Phosphorus atoms provide weakly bound electrons that can flow.weakly bound electrons that can flow.

Semiconductors

DiodesDiodes

A A diodediode is a solid-state component that is a solid-state component that combines an n-type and p-type combines an n-type and p-type semiconductor. semiconductor.

• When a voltage is applied across a When a voltage is applied across a diode, electrons flow from the n-type to diode, electrons flow from the n-type to the p-type semiconductor. the p-type semiconductor.

• There is no current if voltage is applied There is no current if voltage is applied in the opposite direction. in the opposite direction.

• A diode can change alternating current A diode can change alternating current to direct current.to direct current.

TransistorsTransistors

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

• A small current flowing through its A small current flowing through its center layer changes its resistance. center layer changes its resistance.

• A transistor can be a switch–the small A transistor can be a switch–the small current can turn another current on or current can turn another current on or off. off.

• A transistor can be an amplifier–a A transistor can be an amplifier–a small voltage applied to one side small voltage applied to one side produces a large voltage on the other produces a large voltage on the other side.side.

Integrated CircuitsIntegrated Circuits

An An integrated circuitintegrated circuit is a thin slice is a thin slice of silicon that contains many solid-of silicon that contains many solid-state components. Integrated state components. Integrated circuits are sometimes called chips circuits are sometimes called chips or microchips. or microchips.

Solid-State Components

A A computercomputer is a programmable device is a programmable device that can store and process information. that can store and process information.

A mobile phone contains many solid-state A mobile phone contains many solid-state components. components.

• Transistors amplify the phone’s Transistors amplify the phone’s incoming signal. incoming signal.

• Capacitors store electric charge.Capacitors store electric charge.• Diodes maintain proper voltage levels Diodes maintain proper voltage levels

in the circuits.in the circuits.

Communications Technology


1.1. What is the function of a transistor in What is the function of a transistor in an electronic device? an electronic device?

a.a. allows current flow in one direction allows current flow in one direction but not the otherbut not the other

b.b. stores electrical charges until they stores electrical charges until they are neededare needed

c.c. acts as a current switch or amplifieracts as a current switch or amplifier

d.d. converts analog signals into digital converts analog signals into digital signalssignals

Assessment Questions2.2. What is the structure of a diode? What is the structure of a diode?

a.a. a combination of an n-type a combination of an n-type semiconductor and a p-type semiconductor and a p-type semiconductorsemiconductor

b.b. a combination of two n-type a combination of two n-type semiconductorssemiconductors

c.c. an n-type semiconductor layer an n-type semiconductor layer between two p-type semiconductorsbetween two p-type semiconductors

d.d. any combination of three any combination of three semiconductorssemiconductors


3.3. Why are devices using integrated circuits smaller Why are devices using integrated circuits smaller than comparable devices that do not use solid-than comparable devices that do not use solid-state components? state components?

a.a. Many components can be built on a single Many components can be built on a single silicon microchip.silicon microchip.

b.b. Solid-state devices do not need as many circuit Solid-state devices do not need as many circuit components.components.

c.c. Each vacuum tube is replaced by one microchip Each vacuum tube is replaced by one microchip that is much smaller.that is much smaller.

d.d. Solid-state devices are smaller because they Solid-state devices are smaller because they don’t need to hold as much electricity.don’t need to hold as much electricity.


1.1. In electronic devices, a digital In electronic devices, a digital signal conveys information by signal conveys information by converting it into a string of 1’s and converting it into a string of 1’s and 0’s. 0’s.

TrueTrueFalseFalse

Download - Chapter 20: Electricity 20.1 Electric Charge and Static Electricity

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