asvab electrical

Electric current (I)

Flow of electric charge.

Unit of current: Ampere (A)

also called an amp.

Unit of voltage

Volt (V).

Unit of resistance:

Ohm (Ω).

Unit of electrical charge:

Coulomb (C).

Unit of electrical power:

Watt (W).

Ammeter

Measures current; connected in series.

Voltmeter

Measures voltage; connected in parallel.

Ohmmeter

Measures resistance.

Multimeter

Measures multiple electrical quantities.

Current and charge formulas

current: I = Q/t

Current and charge formulas

charge: Q = I * t

Current and charge formulas

time: t=Q / I

Current and charge formulas

1 ampere = 1 coulomb per second (1 A = 1 C/s).

Ohm's law formula

Current: I=V / R

Ohm's law formulas

Voltage: V = I * R

Ohm's law formulas

Resistance: R= V / I

Conventional current

Positive (+) to negative (−).

Electron flow

Negative (−) to positive (+).

Electron flow

opposite to conventional current.

Closed circuit

Complete path; current flows.

Open circuit

Broken path; current stops.

Conductor

Allows electricity to flow easily.

Insulator

Resists electricity flowing through it.

Copper

Common conductor.

Rubber and plastic

Common insulators.

Resistance

Opposes the flow of current.

What happens to current when voltage increases and resistance stays constant?

Current increases.

What happens to current when voltage decreases and resistance stays constant?

Current decreases.

What happens to current when resistance increases and voltage stays constant?

Current decreases.

What happens to current when resistance decreases and voltage stays constant?

Current increases.

What happens to total charge when current increases and time stays constant?

total charge increases.

What happens to total charge when time increases and current stays constant?

Total charge increases.

What happens to current in an open circuit

Current stops because the path is broken.

Wire insulation helps

prevent unwanted current flow and electric shock.

Proton

Positive charge (+).

Neutron

Neutral charge (0).

Electron

Negative charge (−).

Nucleus

Contains protons and neutrons.

Electrons

Found in regions surrounding the nucleus.

Equal protons and electrons =

neutral atom

More protons than electrons =

positive charge.

More electrons than protons =

negative charge

Gaining electrons =

negative charge.

Losing electrons =

positive charge.

Net charge =

protons − electrons.

Positive and positive charges

repel

Negative and negative charges

repel.

Positive and negative charges

attract.

Like charges

repel

Opposite charges

attract

Silver

Higher electrical conductivity than copper

Copper

Widely used in electrical wiring because it conducts electricity well and costs less than silver.

Aluminum:

Lightweight; commonly used in overhead power transmission lines.

Resistance:

Opposition to current flow. Unit: ohm (Ω).

Resistivity:

A material's natural opposition to current. Unit: ohm-meter (Ω·m).

Conductivity:

How easily a material conducts electricity.

High conductivity

low resistivity.

AWG

American Wire Gauge; measures wire thickness.

Smaller AWG number

thicker wire.

Larger AWG number

thinner wire.

Resistance formula

R = pl / A

whats the letter mean R= pL / a

R = Resistance ρ = Resistivity ρ = Resistivity A = Cross-sectional area

Length and resistance have a

direct relationship.

Length doubles affects resistance

resistance doubles.

Length triples affects resistance

resistance triples.

Length is reduced by half affects resistance

resistance is reduced by half.

Area and resistance have an

inverse relationship.

Area triples affects resistance

resistance becomes ⅓.

Area is cut in half affects resistance

resistance doubles.

Area is reduced to ¼

resistance becomes 4 times greater.

Higher temperature

higher resistance in typical metal wires.

Lower temperature

lower resistance in typical metal wires.

Cross-sectional area

amount of space inside a wire when you look at its cut end.

Larger cross-sectional area

lower resistance.

Smaller cross-sectional area

higher resistance.

Double the wire length

double the resistance.

Double the cross-sectional area

half the resistance.

Higher resistance value

greater opposition to electric current.

For copper wire, higher temperature

higher resistance.

Stranded wire

Made of many small metal wires bundled together to form one conductor.

Solid wire

Made from one continuous piece of metal.

Main advantage of stranded wire

More flexible than solid wire.

Stranded wire uses:

Commonly used in equipment that moves, bends, or vibrates.

Repeated bending:

Can weaken wire over time.

Metal fatigue:

Weakening of metal caused by repeated bending or stress

Solid wire

Generally suitable for stationary installations that do not require frequent bending.

Electrical conductivity

Both solid and stranded wires can conduct electricity.

Electrical resistance:

Both types of wire have resistance.

Stranded wire

many small strands and has greater flexibility.

Solid wire

one conductor and has less flexibility