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Chapter 16 Electric Forces and Fields Section 1

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Electricity Static Electricity- a buildup of electrons - Ex: sliding your feet across the carpet Current Electricity- flow of electrons - Ex: car battery

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Electric Charge Electric Charge- electrical property of matter that creates electric and magnetic forces and interactions There are two kinds of electric charge - Positive Charge - Negative Charge Like charges repel Unlike charges attract

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Electric Charge cont’d Electric charge is conserved Example: When a balloon is rubbed against your hair, electrons are transferred to the balloon. Your hair becomes positive and the balloon gains a negative charge

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Electric Charge Atoms consist of protons, electrons, and neutrons Unit of electric charge: Coulomb, C Mass of proton: +1.6 x 10^-19 Mass of electron: -1.6 x 10^-19

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Transfer of Electric Charge Charging by friction: - one material gains electrons and becomes negatively charged while the other loses electrons and becomes positively charged Ex: sliding your feet across the carpet

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Transfer of Electric Charge Charge by contact: When a negatively charged object touches a neutral object. Electrons flow from the rod to the doorknob. The doorknob now has a negative charge.

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Transfer of Electric Charge Induced charge: A negatively charged rod is brought near a neutral doorknob. The charges on the doorknob will redistribute themselves.

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Transfer of Electric Charge Electrical conductors- a material in which charges can move freely - Ex: copper, aluminum Electrical insulators- a material in which charges cannot move freely - Ex: glass, rubber, silk, plastic

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Transfer of Electric Charge Semiconductors- have electrical properties between insulators and conductors Superconductors- have zero electrical resistance; can conduct electricity indefinitely without heating

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Chapter 16 Electricity Section 2

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Electric Force Electric force- the force of attraction or repulsion between objects due to charge Depends on charge and distance

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Electric Force Electric Field- a region in space around a charged object that causes a stationary charged object to experience an electric force

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Current Electrical Potential Energy- the ability to move an electric charge from one point to another The electrical potential energy between two negative charges decreases as the distance between them increases.

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Current Potential Difference- the work that must be done against electric forces to move a unit charge from one point to the other SI unit: volt, V a.k.a voltage

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Current Current- the rate that electric charges move through a conductor SI unit: ampere, A (amp)

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Electrical Resistance Resistance- the opposition posed by a material or a device to the flow of current Caused by internal friction, which slows the movement of charges through a conducting material.

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Electrical Resistance SI unit of resistance: ohm, Ω Equation: resistance = voltage R = V current I

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Example A nine volt battery supplies power to a cordless curling iron with a resistance of 18 ohms. How much current is flowing through the curling iron?

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Example A 110 volt wall outlet supplies power to a strobe light with a resistance of 2200 ohms. How much current is flowing through the strobe light?

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Example A CD player with a resistance of 40 ohms has a current of 0.1 amps flowing through it. Sketch the circuit diagram and calculate how many volts supply the CD player?

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Chapter 16 Electricity Section 3

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Circuits Electric Circuit- a set of electrical components connected such that they provide one or more complete paths for the movement of charges. An electric circuit is a path through which charges can be conducted

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Circuits Closed Circuit- this is the conducting path produced when (for example) a light bulb is connected across a battery’s terminals Open Circuit- results when there is no complete path, this means there is no charge flow and no current

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Circuits Switch- used to open and close a circuit - Ex: Light switch in your home Schematic Diagram- a diagram that depicts the construction of an electrical circuit or apparatus

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Circuits Series- the components of a circuit that form a single path for current Parallel- a circuit in which all of the components are connected to each other side by side

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Circuits Electrical Energy- the energy that is associated with charged particles because of their positions Electric Power is the rate at which electrical energy is used in a circuit

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Circuits Electric Power Equation: Power = current x voltage or P = IV SI unit: watt, W

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Circuits Example: When a hair dryer is plugged into a 120 V outlet, it has a 9.1 A current in it. What is the hair dryer’s power rating?

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Circuits Fuse- an electrical device that contains a metal strip that melts when current in the circuit becomes too great Fuses “blow out” when the current in the circuit reaches a certain level

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Circuits Circuit Breaker- a switch that opens a circuit automatically when the current exceeds a certain value When the current exceeds a certain level the circuit breaker acts as a switch and opens the circuit. These can be reset unlike fuses.

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Chapter 16 Electricity Capacitance

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Capacitance Ability of a conductor to store energy Energy is electricity

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Capacitance Formula Capacitance = charge on each plate potential difference SI Unit: farad, F

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Capacitance Depends on: 1. Size of capacitor 2. Shape of capacitor

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Capacitance Also depends on material between capacitor’s plates Called a dielectric: insulating material (air, glass, rubber, or waxed paper)

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Capacitance A dielectric material between plates increases the capacitance When plates of capacitor are connected, they will discharge the stored energy

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Resistors in Series Carry the same current Total current depends on amount of resistors in the circuit

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Resistors in Series To find total current you must find the equivalent resistance Then use it to find the current

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Equivalent Resistance Sum of the resistor’s in a circuit

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Resistors in Parallel Have the same voltage (potential difference) across them Sum of currents in parallel resistors = total current

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Resistors in Parallel Calculated by formula on page 653 in textbook

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AC Current Current changes direction Electrons flow first one way, then in the opposite direction

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Direct Current Current always flows in one direction Example: Batteries

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Voltage in the United States Transferred at 120 volts Must be stepped up or stepped down by transformer

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