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Chapter 13: Electricity
Section 1: Electric Charge
Positive and Negative Charge
Atoms contain particles called protons, neutrons, and electrons.
Protons and electrons have electric charge, and neutrons have no electric charge.
Protons have positive electric charge and electrons have negative electric charge.
The amount of positive charge on a proton equals the amount of negative charge on an electron
Objects with no net charge are said to be electrically neutral.
Electrons are bound more tightly to some atoms and molecules.
Static Electricity: The accumulation of excess electric charge on an object
Law of Conservation of Charge: Charge can be transferred from object to object, but it cannot be created or destroyed.
Positive and negative charges exert forces on each other.
The force between any two objects that are electrically charged decreases as the objects get farther apart.
Surrounding every electric charge is an electric field that exerts forces on other electric charges.
Many of the forces that act on objects are due to the electric forces between atoms and molecules
The frictional force between two surfaces in contact is due to the attractive electric forces between the atoms on the two surfaces.
Conductors and Insulators
As you walk across a carpeted floor, excess electrons can accumulate on your body. When you reach for a metal doorknob, electrons flow from your hand to the doorknob and you see a spark.
Conductor: A material in which electrons are able to move easily
The best electrical conductors are metals.
Insulator: A material in which electrons are not able to move easily
The plastic coating around wires is an insulator. A damaged electrical cord is hazardous when the conducting wire is exposed
Charging Objects
Rubbing two materials together can result in a transfer of electrons.
Charging by Contact: The process of transferring charge by touching or rubbing
Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object.
Charging by Induction: The rearrangement of electrons on a neutral object caused by a nearby charged object
Lightning is a large static discharge.
A static discharge is a transfer of charge between two objects because of a buildup of static electricity.
A thundercloud is a mighty generator of static electricity.
The electrical energy in a lightning bolt rips electrons off atoms in the air and produces great amounts of thermal energy.
The sensitive electronics in a computer can be harmed by large static discharges.
Earth is a large, neutral object that is also a conductor of charge.
Connecting an object to Earth with a conductor is called grounding.
A lightning rod directs the charge from a lightning bolt safely to the ground.
Detecting Electric Charge
The presence of electric charges can be detected by an electroscope.
If a glass rod is rubbed with silk, electrons move away from the atoms in the glass rod and build up on the silk.
Section 2: Electric Current
Current and Voltage Difference
When a spark jumps between your hand and a metal door- knob, electric charges move quickly from one place to another.
Electric Current: The net movement of electric charges in a single direction
Electric current is measured in amperes.
In a metal wire, or any material, electrons are in constant motion in all directions.
The movement of an electron in an electric current is similar to a ball bouncing down a flight of stairs.
Electric forces in a material cause electric current to flow.
Voltage Difference: related to the force that causes electric charges to flow.
Voltage difference is measured in volts.
Water or electric current will flow continually only through a closed loop. If any part of the loop is broken or disconnected, the flow stops.
Circuit: A closed path that electric current follows
Batteries
A battery can provide the voltage difference that is needed to keep current flowing in a circuit.
A cell consists of two electrodes surrounded by a material called an electrolyte.
Chemical reactions in batteries produce a voltage difference between the positive and negative terminals.
The cell is called a dry cell because the electrolyte is a moist paste, not a liquid solution.
A wet cell contains two connected plates made of different metals or metallic compounds in a conducting solution. A wet-cell battery contains several wet cells connected together.
Most car batteries are lead-acid batteries
A lead-acid battery contains a series of six wet cells made up of lead and lead dioxide plates in a sulfuric acid solution.
Resistance: the tendency of a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.
As electrons move through the filament in a lightbulb, they bump into metal atoms. Due to the collisions, the metal heats up and starts to glow.
Electrical conductors have much less resistance than insulators.
Resistance is measured in ohms (Ω).
Copper is an excellent conductor and has low resistance to the flow of electrons.
The electric resistance of most materials usually increases as the temperature of the material increases.
The Current in a Simple Circuit
A simple electric circuit contains a source of voltage difference, such as a battery, a device that has resistance, such as a lightbulb, and conductors that connect the device to the battery terminals.
The amount of current flowing through a circuit is related to the amount of resistance in the circuit.
Ohm’s Law: the current in a circuit equals the voltage difference divided by the resistance.
Section 3: Electrical Energy
Series and Parallel Circuits
Circuits usually include three components.
One is a source of voltage difference that can be provided by a battery or an electrical outlet.
Another is one or more devices that use electrical energy.
Circuits also include conductors such as wires that connect the devices to the source of voltage difference to form a closed path.
To use electrical energy, a complete circuit must be made.
Series Circuit: the current has only one loop to flow through
A series circuit provides only one path for the current to follow.
Series circuits are used in flashlights and some holiday lights.
When any part of a series circuit is disconnected, no current flows through the circuit. This is called an open circuit.
Parallel Circuit: contain two or more branches for current to move through.
In parallel circuits, the current follows more than one path.
The current can flow through both or either of the branches.
Houses, automobiles, and most electrical systems use parallel wiring so individual parts can be turned off without affecting the entire circuit.
Household Circuits
The wiring in a house must allow for the individual use of various appliances and fixtures.
In a house, many appliances draw current from the same circuit.
To protect against overheating of the wires, all household circuits contain either a fuse or a circuit breaker.
Too many appliances in use at the same time is the most likely cause of the overheating of the circuit.
A circuit breaker contains a piece of metal that bends when the current in it is so large that it gets hot. The bending causes a switch to flip and open the circuit, stopping the flow of current.
Electrical Power: The rate at which electrical energy is converted to another form of energy
The reason why electricity is so useful is that electrical energy is converted easily to other types of energy.
The electrical power used depends on the voltage difference and the current.
Electrical Power Equation: electrical power (in watts) = current (in amperes) X voltage difference (in volts)
The cost of using an appliance can be computed by multiplying the electrical energy used by the amount the power company charges for each kWh.
Chapter 13: Electricity
Section 1: Electric Charge
Positive and Negative Charge
Atoms contain particles called protons, neutrons, and electrons.
Protons and electrons have electric charge, and neutrons have no electric charge.
Protons have positive electric charge and electrons have negative electric charge.
The amount of positive charge on a proton equals the amount of negative charge on an electron
Objects with no net charge are said to be electrically neutral.
Electrons are bound more tightly to some atoms and molecules.
Static Electricity: The accumulation of excess electric charge on an object
Law of Conservation of Charge: Charge can be transferred from object to object, but it cannot be created or destroyed.
Positive and negative charges exert forces on each other.
The force between any two objects that are electrically charged decreases as the objects get farther apart.
Surrounding every electric charge is an electric field that exerts forces on other electric charges.
Many of the forces that act on objects are due to the electric forces between atoms and molecules
The frictional force between two surfaces in contact is due to the attractive electric forces between the atoms on the two surfaces.
Conductors and Insulators
As you walk across a carpeted floor, excess electrons can accumulate on your body. When you reach for a metal doorknob, electrons flow from your hand to the doorknob and you see a spark.
Conductor: A material in which electrons are able to move easily
The best electrical conductors are metals.
Insulator: A material in which electrons are not able to move easily
The plastic coating around wires is an insulator. A damaged electrical cord is hazardous when the conducting wire is exposed
Charging Objects
Rubbing two materials together can result in a transfer of electrons.
Charging by Contact: The process of transferring charge by touching or rubbing
Because electrical forces act at a distance, charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object.
Charging by Induction: The rearrangement of electrons on a neutral object caused by a nearby charged object
Lightning is a large static discharge.
A static discharge is a transfer of charge between two objects because of a buildup of static electricity.
A thundercloud is a mighty generator of static electricity.
The electrical energy in a lightning bolt rips electrons off atoms in the air and produces great amounts of thermal energy.
The sensitive electronics in a computer can be harmed by large static discharges.
Earth is a large, neutral object that is also a conductor of charge.
Connecting an object to Earth with a conductor is called grounding.
A lightning rod directs the charge from a lightning bolt safely to the ground.
Detecting Electric Charge
The presence of electric charges can be detected by an electroscope.
If a glass rod is rubbed with silk, electrons move away from the atoms in the glass rod and build up on the silk.
Section 2: Electric Current
Current and Voltage Difference
When a spark jumps between your hand and a metal door- knob, electric charges move quickly from one place to another.
Electric Current: The net movement of electric charges in a single direction
Electric current is measured in amperes.
In a metal wire, or any material, electrons are in constant motion in all directions.
The movement of an electron in an electric current is similar to a ball bouncing down a flight of stairs.
Electric forces in a material cause electric current to flow.
Voltage Difference: related to the force that causes electric charges to flow.
Voltage difference is measured in volts.
Water or electric current will flow continually only through a closed loop. If any part of the loop is broken or disconnected, the flow stops.
Circuit: A closed path that electric current follows
Batteries
A battery can provide the voltage difference that is needed to keep current flowing in a circuit.
A cell consists of two electrodes surrounded by a material called an electrolyte.
Chemical reactions in batteries produce a voltage difference between the positive and negative terminals.
The cell is called a dry cell because the electrolyte is a moist paste, not a liquid solution.
A wet cell contains two connected plates made of different metals or metallic compounds in a conducting solution. A wet-cell battery contains several wet cells connected together.
Most car batteries are lead-acid batteries
A lead-acid battery contains a series of six wet cells made up of lead and lead dioxide plates in a sulfuric acid solution.
Resistance: the tendency of a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.
As electrons move through the filament in a lightbulb, they bump into metal atoms. Due to the collisions, the metal heats up and starts to glow.
Electrical conductors have much less resistance than insulators.
Resistance is measured in ohms (Ω).
Copper is an excellent conductor and has low resistance to the flow of electrons.
The electric resistance of most materials usually increases as the temperature of the material increases.
The Current in a Simple Circuit
A simple electric circuit contains a source of voltage difference, such as a battery, a device that has resistance, such as a lightbulb, and conductors that connect the device to the battery terminals.
The amount of current flowing through a circuit is related to the amount of resistance in the circuit.
Ohm’s Law: the current in a circuit equals the voltage difference divided by the resistance.
Section 3: Electrical Energy
Series and Parallel Circuits
Circuits usually include three components.
One is a source of voltage difference that can be provided by a battery or an electrical outlet.
Another is one or more devices that use electrical energy.
Circuits also include conductors such as wires that connect the devices to the source of voltage difference to form a closed path.
To use electrical energy, a complete circuit must be made.
Series Circuit: the current has only one loop to flow through
A series circuit provides only one path for the current to follow.
Series circuits are used in flashlights and some holiday lights.
When any part of a series circuit is disconnected, no current flows through the circuit. This is called an open circuit.
Parallel Circuit: contain two or more branches for current to move through.
In parallel circuits, the current follows more than one path.
The current can flow through both or either of the branches.
Houses, automobiles, and most electrical systems use parallel wiring so individual parts can be turned off without affecting the entire circuit.
Household Circuits
The wiring in a house must allow for the individual use of various appliances and fixtures.
In a house, many appliances draw current from the same circuit.
To protect against overheating of the wires, all household circuits contain either a fuse or a circuit breaker.
Too many appliances in use at the same time is the most likely cause of the overheating of the circuit.
A circuit breaker contains a piece of metal that bends when the current in it is so large that it gets hot. The bending causes a switch to flip and open the circuit, stopping the flow of current.
Electrical Power: The rate at which electrical energy is converted to another form of energy
The reason why electricity is so useful is that electrical energy is converted easily to other types of energy.
The electrical power used depends on the voltage difference and the current.
Electrical Power Equation: electrical power (in watts) = current (in amperes) X voltage difference (in volts)
The cost of using an appliance can be computed by multiplying the electrical energy used by the amount the power company charges for each kWh.