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 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 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 Ohm’s Law

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 Electric Power Electrical Energy

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