ASVAB Electronics

Electricity

General term for the variety of phenomena resulting from the presence and flow of electric current

Volts

Amperes (amps)

Ohms

3 ways Electricity is measured

Volts

Measure the difference of potential between 2 points

Amperes (amps)

Measure the number of electrons that move past a specific point in 1 second

(i.e. electrical currents)

Ohms

Measure resistance, including anything that could limit the flow of electrons

Current

Electrical ___ occurs when electrons move from one place to another.

Conductors

(e.g. copper, silver, water)

A substance, body, or device that conducts electricity; allows the electrons to move freely.

Insulators

(e.g. rubber, wood)

A material of such low conductivity that does not easily allow the flow of electrical current to pass through it; discourages electrical current

Watt

This measures power, the rate at which electrical energy is consumed or transformed into another type of energy, such as light or heat

Power

The rate at which electrical energy is consumed or transformed into another type of energy, such as light or heat

Watt-hour

This is the amount of energy used in 1 hour at a rate of 1 watt.

Kilowatt-hour

The amount of energy used in 1 hour at a rate of 1,000 watts(i.e.1-kilowatt)

True

True or False

Most electricity is measured in kilowatt-hours

Wattage x Time (expressed in hours)

To find watt-hours multiply ___ by ___.

10 kilowatt-hours

How many kilowatt-hours is enough energy to run a 10,000-watt speaker system for 1 hour?

2 hours

10 kilowatt-hours is enough energy to run a 5,000-watt air conditioner for how long?

10 hours

10 kilowatt-hours is enough energy to run a 1,000-watt waffle iron for how long?

Circuit

The path of an electrical current

Open

When there is literally an open space in the circuit that prohibits current from flowing

Short

When the open space of a circuit has been closed to allow current to flow

Voltage

The difference of the pressure between 2 points in a circuit

(sometimes called voltage drop or difference of potential)

True

True or False

To see what the voltage is anywhere in a circuit, you have to compare the voltage at that point to ground

Ground

(e.g. base of a lamp, chassis of a car)

Any part of a circuit (or other object that has electricity running through it) that measures 0 volts

Voltmeter or multimeter

Measures voltage in a circuit

Voltmeter

An instrument used for measuring electrical potential difference between two points in an electric circuit (i.e. voltage)

A voltmeter has 2 leads. To measure voltage, you place one lead somewhere in the circuit and one lead at another location in the circuit. The voltmeter tells you what the voltage is between those 2 points.

How to use a voltmeter:

Cell

A storage compartment for electricity in a battery that has a specific voltage.

True

True or False

You can figure out the number of cells a battery has by dividing the voltage of the battery by the volts.

Electrical current

The flow (rate of flow) of electrons in a conductor

coulombs (C), which measure charge.

Current flow can be expressed in terms of ___.

Coulomb

The amount of electricity provided by a current of 1 ampere flowing for 1 second.

True

True or False

If 1 coulomb (about 6,241,500,000,000,000,000 electrons) flows past a specified point in 1 second, that's a flow rate of 1 ampere (amp, abbreviated A).

Ammeters

Measure the flow of current through a circuit

True

True or False

Typically current is tiny, so small that it's measured in milliamperes; 1 milliampere is one-thousandth of an ampere.

Circuit breaker

A device that automatically interrupts the electrical current.

True or False

True or False

Sometimes a circuit must be opened in order to add or remove resistance. In other words, the flow of electricity must be interrupted in order to physically change the resistance.

Rheostat

A device which can vary the resistance without opening the circuit - the electrical device can continue to work even as the resistance is altered

A dimmer switch on a light; you increase the amount of resistance to dim the light and decrease the resistance to brighten the light

Example of a rheostat

Ohms (Ω)

The SI unit of electrical resistance; measures the amount of resistance that interferes with the flow

Ohmmeter

Device that measures the amount of resistance that interferes with the flow

The amount of voltage (measured in volts)

The resistance to the current (measured in ohms)

The amount of current (measured in amps)

The 3 influences that are present when current flows through a wire

The current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance.

What is Ohm's law

I

Abbreviation for current

E

Abbreviation for voltage

R

Abbreviation for resistance

Current (amperes) = Voltage(volts)/Resistance(ohms)

OR

I = E / R

Formula to solve for Current

(Ohm's law)

Voltage = Current x Resistance

OR

E=IR

Formula to solve for Voltage

(Ohm's law)

Resistance = Voltage/Current

OR

R = E / I

Formula to solve for Resistance

(Ohm's law)

Watts

Unit of power in the International System of Units (SI)

750 watts

How many watts are to 1 horsepower

True or False

One kilowatt represents 1,000 watts

By multiplying the number of kilowatts (kW) required by the number of hours of use.

(e.g. if you use a 40-watt light bulb 5 hours a day, you've used 200 watt-hours, or 0.2 killowatt-hours of electrical energy)

How are kilowatt-hours determined?

Least

Electricity follows the path of ___ resistance.

Conventional Current

The vacancies left by electrical particles "moving" from the positive (+) terminal to the negative (-) terminal of a battery.

(in regards to electrical flow of current)

True

True or False

The military teaches current flow based on the flow of the electrons, and electrons, no matter how you look at it, flow from the negative terminal to the positive terminal

Short circuit

This occurs when any wire accidentally crosses over another wire, causing the electricity to bypass the rest of the circuit and not follow the intended path

Chemical Effect

Heat Effect

Magnetic Effect

Physiological Effect

4 effects produced by current and some of their commercial applications

Chemical Effect

Current produces this effect when it passes through a chemical compound and breaks that compound up.

(Also called Electrolytic Decomposition, this phenomenon is used in Electroplating)

Electroplating

A process used to cover objects with a very thin coating of metal.

(chemical effect)

Heat Effect

Conducting electricity causes wires to become heated. Heat develops because the current must overcome the resistance of the wire. This heat energy can be quite obvious or hardly noticeable to touch, depending on the size of the wire and the amount of current

Magnetic Effect

When a wire is introduced into a magnetic field, electricity flows through the wire and creates a magnetic field that repels a magnet. This effect is used to create energy through Electromagnetic Induction. If the wire is wrapped around an iron core and a current is sent through the wire, the iron become magnetized.

Electromagnetic Induction

The production of electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, etc.

Physiological Effect

Current produces this effect when it passes through your bicep (or any other muscle) and causes the muscle to contract. This effect is used in medicine.

Direct Current (DC)

Current that only and always flows in one direction

Alternating Current (AC)

Current that constantly changes direction in a regular patter

AC

Most electricity comes in the form of __.

Alternating Current

Higher voltages are easier to obtain with ___ current.

Frequency

The number of times a current completes 2 alternations of direction per second

Hertz (Hz)

The unit of measurement for frequency

True

True or False

One hertz (Hz) equals one complete cycle per second. In other words, the current makes two complete alternations of direction.

60 Hz

The Alternating Current (AC) in your house probably completes 60 alternating cycles per second. Therefore, the AC in your house has a frequency of ___ Hz.

1000 Hertz (Hz)

1 kilohertz (kHz) = ___ Hz.

1 million Hertz (Hz)

1 megahertz (MHz) = ___ Hz.

1 billion Hertz (Hz)

1 gigahertz (GHz) = ___ Hz.

Capacitive reactance (capacitance)

Inductive reactance (inductance)

2 properties of alternating currents that impede the flow of current

Capacitive reactance (capacitance)

The storage of energy that occurs in a nonconductor. This property resists any change in voltage in a circuit.

Inductive reactance (inductance)

The property that causes an electromotive force (another way of saying voltage) to be induced in a circuit.

Impedance = Electromotive force / Current

Formula for Impedance

Capacitors and Inductors

Devices used in circuits to provide the type of reactance needed.

Microfarad (μF)

Capacitors are rated in ___.

Millihenries (mH)

Inductors are rated in ___.

Rectification

The process of making certain electronic circuits change alternating current to direct current.

(i.e. changes incoming AC to DC)

Rectifiers

The circuits that perform rectification

Semiconductor Diodes

Found in rectifiers; a component made of a material with conductivity somewhere between that of a conductor and an insulator

Diodes

These conduct electricity in only one direction.

Inductors and Capacitors

Rectification often requires ___ and ___.

Cooler

Variable

Rectification helps appliances run at ___ temperatures and allows them to run at ___ speeds.

Direct

Devices typically need ___ current to run properly.

Semiconductor

An object that conducts electricity poorly at low temperatures.

Transistor

A semiconductor that controls the flow of electricity in a circuit. Usually made of germanium or silicon.

This electrical device can amplify a signal.

True

True or False

Transistors are small, require little power, and last a long time

Emitter

Base

Collector

3 terminals a transistor contains

Emitter

The voltage output

(transistor)

Base

This acts like a gate, and the voltage at the base controls the flow of current through the transistor (and therefore the voltage)

Collector

The voltage input

(transistor)

Block diagrams

Used to show the various combined circuits that form a complex system

Wires

Used to pass current from one part of the component to another

Joined wires

Wires that are connected to each other and are indicated by a dark circle in diagrams

Unjoined wires

Wires that are not connected; in circuit diagrams, it is necessary to draw wires crossing even though they aren't connected, this is indicated by a hump symbol

Cell

This supplies electrical current.