Electrical Principles & Technologies 9

What is electricity?

Flow of electrons

What are the 3 atom charges?

Protons (+)

Electrons (-)

Neutrons (equal + and - charges)

What is the law of electrical charge?

• opposite charges attract

• like charges repel eachother

• charged attract uncharged (neutrons)

What are ion-(charged particles)?

groups of atoms that are charged

• anion - ion gains electrons

• cation- ion loses electrons

• involved in static electricity

What is static electricity?

stationary, uncontrolled electric charge

• sudden transfer of electrons

• opposite charges attract

• electric charges are created when materials are pulled apart or rubbed together

• results may be sparks, shocks, or material clinging together

What is current electricity?

steady flow of controlled, charged particles

• flows until source is used up or disconnected

What is a (I) current?

rate that (an) electric charge flows in a conductor

• how many electrons that are moving through the wire

• measured in amps/amperes (A)

  • Galvanometer: used to measure and detect small currents

  • Ammeter: used to measure currents

What are conductors?

• holds electrons loosely

• allows charges to move freely

  • copper, steel, gold, silver, sea water

• Semi-conductors

  • higher conductivity than insulators, lower conductivity that conductors

• Super conductors

  • no resistance

  • some materials become super conductors in low temperatures

What are insulators?

Hold electrons very tightly

• do not allow charges to move freely or through them

What is a circuit?

a path where electrons (from a voltage or current source) flow

What is required to make a bulb work?

• a complete circuit

• electricity needs to be flowing in a continuous path

What are the 4 elements of a circuit?

• energy source (battery)

• energy load (lightbulb or resistor)

• conducting wires

• control (switch)

What are resistors?

types of conductors that allow electric currents through but with resistance, limiting the amount of current

• Light bulbs

  • the higher the resistance, the more energy gained by the resistor which is radiated into heat or light energy

What are series?

Type of circuit

• one current path

• voltage divides

• current is constant

What is a parallel circuit?

• several current path

• current divides

• voltage is constant

• a set of branches

What is needed for a continuous current?

• to make a continuous current:

  • source of electrical charges

  • a conducting path (copper, silver, aluminum)

  • device to use electrical charge (load)

What is voltage?

electrical push which gives the cell current (electric pressure)

• provides energy for moving electrons

• measured in volts (V)

What is resistance?

property of a substance that hinders the movement of electric charge and converts electric energy to other energy

• measure of how difficult it is for electrons to flow through a substance

• measured in ohms

• good conductors have less resistance, meaning less energy loss

What type of wire is used for the filament of a light bulb?

Tungsten

• has a 400x greater resistance than other wires

What is a branch?

a part of circuit

What is ohms law?

V = I x R

• relationship between voltage, current, and resistance

• founded by Georg Simon Ohm

What 4 things make up a common circuit resistor?

heat-conducting ceramic

• carbon

• metal oxide

• metal film

• resistance wire

What are 3 variables that could alter resistance of a variable resistor?

• light

• voltage

• temperature

What is a variable resistor?

A device that lets you change the resistance

• controls things like brightness and volume

What is an ohmic resistor?

Resistor that has a constant resistance

• voltage and current are linear

• follows ohms law

What are 3 variable resistors and their uses?

Rheostat - control light brightness

Varistor - voltage/surge protector (protects circuits)

Thermistor - controls and monitor temperatures

What are surges?

A sudden increase/spike in voltage

What is a disadvantage of a parallel circuit?

When using an appliance the current (flow of electric charge) closest to your source increases- if current increases too much wires become hot which could lead to fire

• more current = more temperature

How are fires prevented in wires?

fuse/wind breakers

What 4 factors affect wire resistance?

Length

• resistance increases with length- if length doubles, resistance doubles

Cross-sectional Area (Thickness)

• resistance decreases with thickness- if thickness doubles, resistance is half as great

Temperature

• as wire temperatures increases, resistance increases

Material

• the structure of atoms allow electrons to move more freely than others in metals

What are 3 forms of energy?

heat, light, and kinetic energy

• they can be converted into each other

What type of energy conversion do thermocouples have?

heat > electricity

• thermocouples were designed through the seebeck effect

What is the seebeck effect?

• when one metal junction is heated in a thermocouple (one side hot, one cold), they generate a voltage (the difference in electric energy causes electrons to move)

What type of energy conversion does piezoelectricity have?

kinetic energy > electricity

What type of energy conversion do light-emitting diodes have?

LED

• electrical energy passes through semiconducting chip that causes electrons to lose photons (light energy)

Fluorescent

• makes lights through gas or vapour

Incandescent

• makes light through metal filaments (tungsten)

What type of energy conversion do solar/photovoltaic cells have?

Light > electricity

What are thermocouple?

• it’s a loop of 2 different metal wires combined with a constentan, the metal wires are wrapped together at both ends, called junctions

What is piezoelectric effect?

• piezoelectric effect is when electric current produces vibrations in a tiny crystal (rochelle salt or quartsz) that causes the crystal to contract or expand slightly- any material touching crystal creates sound waves/vibrations

What are solar/photovoltaic cells?

cells made from semi-conducting material that absorbs light that causes electrons to break loose

• the free electrons flow through metal contacts to create current to be used in electrical devices

  • solar panels

What is an electrolyte?

A liquid substance that can conduct electricity

• allows electricity to flow through movement of ions

What is a wet cell?

uses liquid electrolyte

What is a dry cell?

has a paste, plastic, or ceramic solid electrolyte

What is an electrode?

a solid material (usually metal) that conducts electricity

• positively charged: cathode

• negatively charged: anode