Introduction to Electricity

Electric Charge and Static Electricity Law of electric

charges

Electric Force

like charges repel and opposite charges attract

force of attraction or repulsion on a charged particle

Electric Field

Charge it

space around charged object in which another charged object experiences electric force

objects become positively charged when it loses electrons

negatively charged when gains electrons

Friction

Conduction

happens when electrons are “wiped” from one object onto another

electrons move from one object to another by direct contact

Induction charges in an uncharged metal object are rearranged without direct contact with a charged object

Conservation of Charge

Detecting Charge

when an object is charged, no charges are created or destroyed

electrons simply move from one atom to another

Electroscope – uncharged = metal leaves hang down; charged = metal leaves repel

Electrical Conductor

Electrical Insulator

material in which charged can move freely

most metals, salt solution, graphite

material in which charges cannot move freely

plastic, rubber, glass, wood, air

Static Electricity

Electric Discharge

electric charge at rest produced by friction

or induction “static” = not moving

release of electricity stored in a source

Electric Current and Electrical Energy Electrical Energy

Electric Current

energy of electric charges

rate at which charges pass through a given point

measured in amperes (A); in equations the symbol is I

• Commanding Electrons to Move This electric field is created so quickly that all electrons start moving through the wire at the same instant. Think of the electric field as a command to the electrons to charge ahead.

Two Kinds of Currents:

AC – Alternating Current

DC – Direct Current

charges continually shift from flowing in one direction to flowing in the reverse

charges always flow in same direction

Voltage potential difference between two points

measured in volts (V) amount of energy

released as a charge moves between two points in the path of a current

higher voltage = more energy released

Resistance opposition presented to the current by a material or device

expressed in ohms (Ω)

“electrical friction” higher resistance =

lower the current depends on object’s

material, thickness, length, and temperature

•Resistance and Temperature In general, the resistance of metals increases as temperature rises.

Superconductor

Cells

Electrolytes

Electrodes

material with almost zero resistance when cooled

change chemical or radiant energy into electrical energy

batteries are one or more cells

allow charges to flow

part of cell through which charges enter or exit

Wet Cell

Dry Cell

Thermocouple

liquid electrolytes ex. car battery –

sulfuric acid

electrolytes are solid or paste-like

converts thermal energy into electrical energy

Photocell converts light energy into electrical energy

ex. solar panel

Electrical Calculations Ohm’s Law named after George Ohm,

1826 determined how resistance

and current affect voltage increasing voltage increases

current increasing resistance

decreases current V = I x R or I = V/R V – voltage, I –

current/amps, R – resistance

Electric Power

Electrical Energy

rate at which electrical energy is converted into other forms of energy

power = voltage x current P = V x I

measured in watts (W) or kilowatts (kW)

power x time E = P x t

Electrical Circuits

Electrical Circuit complete path through which a charge can flow

three parts: energy source, wires, a load (light bulb, radio)

sometimes also includes a switch

Open Circuit

Closed Circuit

circuit is broken; electricity will not flow

“turned off”

circuit is complete and electricity will flow

“turned on”

Series Circuit charge has only one path through which it can flow

if one element stop working, none of the elements can work

Parallel Circuit two or more paths through which charges can flow

if one element stops functioning, the rest still operate

Fuse

Circuit Breaker

prevents current overload in a circuit

“blowing a fuse” is when a wire in the center of the fuse melts

switch that opens when current is too high

Grounding transfer of excess charge through a conductor to Earth