Chapter 16 Electric Forces and Fields Section 1

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

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

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

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

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

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.

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

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

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

Chapter 16 Electricity Section 2

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

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

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.

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

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

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.

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

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?

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?

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?

Chapter 16 Electricity Section 3

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

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

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

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

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

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

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?

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

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.

Chapter 16 Electricity Capacitance

Capacitance Ability of a conductor to store energy Energy is electricity

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

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

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

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

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

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

Equivalent Resistance Sum of the resistor’s in a circuit

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

Resistors in Parallel Calculated by formula on page 653 in textbook

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

Direct Current Current always flows in one direction Example: Batteries

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