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Electricity
Electricity
Law of Electrostatics
- Objects with like charges repel
- Objects with opposite charges attract
- Neutral objects are attracted to charged objects
Electric Charge
- Occurs if an atom does not have an equal number of protons and electrons
- Neutral objects: have an equal number of p+ and e-
- Negatively charge objects: have more e- than p+
- Positively charged objects: have more p+ than e-
Ways of Charging
Charging by conduction
- Electric charge can be given to a neutral object by touching it with a charged object
- An object that has been charged by contact always receives the same charge as the charge that is on the object that charges it
Charging by Induction
- The charged object is brought NEAR a neutral one (no contact)
- the neutral object becomes temporarily charged (electrons move around)
- The charges in the neutral object rearrange themselves according to the law of electrostatics
- the neutral object has the OPPOSITE charge as the object that induced it.
Charging by Friction
- When two different neutral materials are rubbed together
- electrons (e-) are transferred from one object to another
- one object will lose e- to another which will gain e-
- different materials have different attractions for elections
Factors That Affect Resistance
- Type of material: the ability of a material to conduct electricity is determined by how freely electrons can move within the material
- Cross-Sectional Area: the diameter of the cross-section gives you a sense of how thick the wire is. Thicker wires have less internal resistance than thinner ones.
- Length: As you increase the length of a wire, its internal resistance increases. This happens because electrons have to travel through more material
- Temperature: Resistance increases when electrons bump into atoms as they move through a material. When wires get warmer, the atoms that make up the wire gain energy and move faster. Resistance increases with temperature.
- Electrical Resistance: the ability of a material to oppose the flow of electric current; measured in ohms.
- Resistor: a device that reduces the flow of electric current
- Ohmmeter: a device that is used to measure resistance
Examples:
- Lightweight carbon resistors are used in electronics
- Heavier ceramic resistors are used in larger circuits
- Dimmer switches and volume controls are other types of resistors called variable resistors
- allows you to change the resistance in a circuit.
Current Electricity
- The controlled flow of electrons through a conductor
- refers to the electric charges (electrons) that flow through a conductor in a controlled way
Forms of Current Electricity
- Direct Current (DC)
- electrons flow in one direction only
- produced by electric cells
- Alternating Current (AC)
- Electrons move back and forth, changing their direction
- produced by generators
Static Electricity
- An imbalance of electric charge on the surface of an object
- Charges are at rest (ie. they do not move)
- The strength of the electric force is related to
- Amount of charge
- Distance between charged objects
Applications of Static Electricity
- Conductor: an object that lets electrons move easily through it
- Eg. metal wires
- Insulator: a material that does not allow the movement of electrons through it
- Eg. plastic
- Grounding: connecting an object to a large body, like Earth, that is capable of removing any electric charge on the object
- Negative object: excess elections flow the object to the Earth until it is neutral
- Positive object: electrons flow from the Earth to the object until it is neutral
Ohms Law
- Adding loads in series increases resistance. Each load acts like a speed bump
- Based on Ohms law, if resistance increases, so do voltage and current decreases.
Electric Cells
- A portable device that converts chemical energy into electrical energy
- Consists of 2 electrodes in a conducting solution (called an electrolyte)
- Electrodes are conductors - one is positively charged and the other is negatively charged
- When electrodes are connected by wires in a circuit, electrons flow - they are repelled b the negative electrode and attract the positive electrode.
Definitions:
- Electrical Energy: the energy provided by the flow of electrons in an electric circuit
- Electric Cell: a device that converts chemical energy into electrical energy
- Primary Cell: an electric cell that may only be used once
- Secondary Cell: an electric cell that can be recharged
Types of Primary Cells
- Primary cells fall into 2 categories: dry cells and wet cells. Chemical reactions use up materials in primary cells as electrons flow from them, thus the cell can be permanently discharged.
- Wet cells consist of metal conductors placed in contact with a conducting liquid
- Dry cells work with wet cells, only a moist paste is used rather than a liquid
Equations
Measurements in Electrical Circuits
Electricity
Electricity
Law of Electrostatics
- Objects with like charges repel
- Objects with opposite charges attract
- Neutral objects are attracted to charged objects
Electric Charge
- Occurs if an atom does not have an equal number of protons and electrons
- Neutral objects: have an equal number of p+ and e-
- Negatively charge objects: have more e- than p+
- Positively charged objects: have more p+ than e-
Ways of Charging
Charging by conduction
- Electric charge can be given to a neutral object by touching it with a charged object
- An object that has been charged by contact always receives the same charge as the charge that is on the object that charges it
Charging by Induction
- The charged object is brought NEAR a neutral one (no contact)
- the neutral object becomes temporarily charged (electrons move around)
- The charges in the neutral object rearrange themselves according to the law of electrostatics
- the neutral object has the OPPOSITE charge as the object that induced it.
Charging by Friction
- When two different neutral materials are rubbed together
- electrons (e-) are transferred from one object to another
- one object will lose e- to another which will gain e-
- different materials have different attractions for elections
Factors That Affect Resistance
- Type of material: the ability of a material to conduct electricity is determined by how freely electrons can move within the material
- Cross-Sectional Area: the diameter of the cross-section gives you a sense of how thick the wire is. Thicker wires have less internal resistance than thinner ones.
- Length: As you increase the length of a wire, its internal resistance increases. This happens because electrons have to travel through more material
- Temperature: Resistance increases when electrons bump into atoms as they move through a material. When wires get warmer, the atoms that make up the wire gain energy and move faster. Resistance increases with temperature.
- Electrical Resistance: the ability of a material to oppose the flow of electric current; measured in ohms.
- Resistor: a device that reduces the flow of electric current
- Ohmmeter: a device that is used to measure resistance
Examples:
- Lightweight carbon resistors are used in electronics
- Heavier ceramic resistors are used in larger circuits
- Dimmer switches and volume controls are other types of resistors called variable resistors
- allows you to change the resistance in a circuit.
Current Electricity
- The controlled flow of electrons through a conductor
- refers to the electric charges (electrons) that flow through a conductor in a controlled way
Forms of Current Electricity
- Direct Current (DC)
- electrons flow in one direction only
- produced by electric cells
- Alternating Current (AC)
- Electrons move back and forth, changing their direction
- produced by generators
Static Electricity
- An imbalance of electric charge on the surface of an object
- Charges are at rest (ie. they do not move)
- The strength of the electric force is related to
- Amount of charge
- Distance between charged objects
Applications of Static Electricity
- Conductor: an object that lets electrons move easily through it
- Eg. metal wires
- Insulator: a material that does not allow the movement of electrons through it
- Eg. plastic
- Grounding: connecting an object to a large body, like Earth, that is capable of removing any electric charge on the object
- Negative object: excess elections flow the object to the Earth until it is neutral
- Positive object: electrons flow from the Earth to the object until it is neutral
Ohms Law
- Adding loads in series increases resistance. Each load acts like a speed bump
- Based on Ohms law, if resistance increases, so do voltage and current decreases.
Electric Cells
- A portable device that converts chemical energy into electrical energy
- Consists of 2 electrodes in a conducting solution (called an electrolyte)
- Electrodes are conductors - one is positively charged and the other is negatively charged
- When electrodes are connected by wires in a circuit, electrons flow - they are repelled b the negative electrode and attract the positive electrode.
Definitions:
- Electrical Energy: the energy provided by the flow of electrons in an electric circuit
- Electric Cell: a device that converts chemical energy into electrical energy
- Primary Cell: an electric cell that may only be used once
- Secondary Cell: an electric cell that can be recharged
Types of Primary Cells
- Primary cells fall into 2 categories: dry cells and wet cells. Chemical reactions use up materials in primary cells as electrons flow from them, thus the cell can be permanently discharged.
- Wet cells consist of metal conductors placed in contact with a conducting liquid
- Dry cells work with wet cells, only a moist paste is used rather than a liquid