Achievable ASVAB

7. Electronics Information

Electricity Basics

5 min read

Atomic structure

As we discussed in Chemistry, the atom contains $3$ parts: electrons, neutrons, and protons. In simplest terms, electricity is all about how electrons move.

Electric charge comes in two kinds, positive and negative: protons carry positive charge and electrons carry negative charge. Most atoms (and the matter they combine to form) are neutral, with no net charge, because the negative charge of their electrons balances the positive charge of their protons. However, when matter interacts with other matter, the two objects can exchange electrons. This exchange alters the charge of both objects, making one object have a net negative charge and the other a net positive charge. This is the same reason you sometimes feel a shock after walking across a carpet and touching a doorknob.

Conductors, insulators & semiconductors

Conductor: a material that allows electrons to flow through it easily. Most metals, like copper and silver, are good conductors, which is why they’re used to make electrical wires.

Insulator: a material that blocks the flow of electricity. Rubber, glass, and plastic are common insulators, which is why they’re used to coat wires and build tools that are safe to handle near electricity.

Semiconductor: a material that can act as both a conductor and an insulator, depending on the conditions. Silicon is the most common semiconductor, and its ability to switch between conducting and insulating is what makes it possible to build the transistors and microchips found in computers and other electronics.

Ohm’s law

A helpful way to picture voltage, current, and resistance is to imagine water flowing through a pipe.

Voltage: the electrical pressure that pushes electrical current through a wire, similar to the water pressure pushing water through a pipe. Voltage is measured in Volts (V).

Current: the flow of electric charge (electrons) through a wire, similar to the flow rate of water through a pipe. Current is measured in Amps (A).

Resistance: an object’s opposition to the flow of electrical current, similar to how a narrow pipe restricts the flow of water. Resistance is measured in Ohms (Ω).

Sidenote

Resistors

Resistors: A device meant to limit the flow of electric current

Fixed resistors: A device that has a fixed resistance. It will always present the same resistance to the circuit.

Variable resistors: The resistance can be mechanically adjusted to change the resistance in a circuit. This is helpful if you want to change the brightness of a light, slow a motor, or change the volume of a speaker. This type of variable resistor is commonly called a potentiometer, or “pot” for short. You’ll find one inside most volume knobs and dimmer switches.

Ohm’s Law is the basis for electronics and describes the relationship between voltage, current, and resistance. It states that:

Voltage = Current × Resistance

$V = I \times R$

Triangle divided into V on top and I, R on bottom, giving Ohm's Law forms: V = I x R, I = V / R, R = V / I — Ohm’s Law Triangle

Let’s work through an example.

A circuit has a current of $2$ amps and a resistance of $5$ ohms. To find the voltage, we plug those numbers into the formula:

$V = I \times R$

$V = 2 \times 5$

$V = 10$ volts

Sometimes you’ll be given the voltage and need to solve for current or resistance instead. You can rearrange Ohm’s Law to solve for any of the three variables:

$I = \frac{V}{R}$

$R = \frac{V}{I}$

To remember the rearrangements, use the triangle above: cover the letter you’re solving for, and the remaining letters give the formula.

Values are often given with metric prefixes: milli (m) means one-thousandth, kilo (k) means $1, 000$ , and mega (M) means $1, 000, 000$ . Convert to base units (volts, amps, ohms) before using Ohm’s law.

Example: Metric prefixes

A $6$ V battery is connected across a $2$ kΩ resistor. What is the current?

$2$ kΩ $= 2, 000$ Ω

$I = \frac{V}{R} = \frac{6}{2 , 000} = 0.003$ A

Answer: $0.003$ A, which is $3$ mA

Knowledge check

If a circuit has a voltage of $12$ volts and a resistance of $4$ ohms, what is the current?

Solution:

(spoiler)

$3$ amps

Measuring instruments

Now that we’ve covered voltage, current, and resistance, let’s look at the tools used to measure them in a real circuit.

Voltmeter: measures voltage. A voltmeter is connected in parallel with a component of the circuit, since voltage is measured across two points.

Ammeter: measures current. Unlike a voltmeter, an ammeter must be connected in series with a component, since current has to flow through the meter to be measured.

Ohmmeter: measures resistance. An ohmmeter sends its own small current through a component and calculates its resistance from that, so it should only be used on a component that’s disconnected from any power source.

Multimeter: a single device that combines a voltmeter, ammeter, and ohmmeter into one tool, letting you measure voltage, current, or resistance without needing three separate instruments. Most multimeters can be switched between these modes.

Atomic structure & electricity basics

Atoms have electrons, neutrons, protons; electricity concerns electron movement
Two kinds of charge: positive (protons) and negative (electrons)
Neutral object: electrons balance protons, so no net charge; exchanging electrons creates net positive/negative objects (e.g., static shock)

Conductors, insulators & semiconductors

Conductor: allows electron flow easily (metals like copper, silver — used in wires)
Insulator: blocks electrical flow (rubber, glass, plastic — used for safety coatings)
Semiconductor: can act as either, depending on conditions (silicon — basis of transistors/microchips)

Ohm’s Law & circuit quantities

Voltage (V, Volts): electrical pressure pushing current, like water pressure
Current (I, Amps): flow of electric charge, like water flow rate
Resistance (R, Ohms Ω): opposition to current flow, like a narrow pipe
Ohm’s Law: $V = I \times R$ , with rearrangements $I = \frac{V}{R}$ and $R = \frac{V}{I}$
- Use the V/I/R triangle: cover the unknown variable to get the formula
Resistors limit current: fixed resistors (constant resistance) vs. variable resistors/potentiometers (adjustable, used in volume/dimmer controls)
Convert metric prefixes (milli = $0.001$ , kilo = $1, 000$ , mega = $1, 000, 000$ ) to base units before calculating

Measuring instruments

Voltmeter: measures voltage; connected in parallel
Ammeter: measures current; connected in series (current must flow through it)
Ohmmeter: measures resistance; sends its own current, so component must be disconnected from power
Multimeter: combines voltmeter, ammeter, and ohmmeter into one switchable device

Next | 7.2 Circuits

Electricity Basics

Atomic structure

As we discussed in Chemistry, the atom contains $3$ parts: electrons, neutrons, and protons. In simplest terms, electricity is all about how electrons move.

Conductors, insulators & semiconductors

Conductor: a material that allows electrons to flow through it easily. Most metals, like copper and silver, are good conductors, which is why they’re used to make electrical wires.

Ohm’s law

A helpful way to picture voltage, current, and resistance is to imagine water flowing through a pipe.

Voltage: the electrical pressure that pushes electrical current through a wire, similar to the water pressure pushing water through a pipe. Voltage is measured in Volts (V).

Current: the flow of electric charge (electrons) through a wire, similar to the flow rate of water through a pipe. Current is measured in Amps (A).

Resistance: an object’s opposition to the flow of electrical current, similar to how a narrow pipe restricts the flow of water. Resistance is measured in Ohms (Ω).

Sidenote

Resistors

Resistors: A device meant to limit the flow of electric current

Fixed resistors: A device that has a fixed resistance. It will always present the same resistance to the circuit.

Ohm’s Law is the basis for electronics and describes the relationship between voltage, current, and resistance. It states that:

Voltage = Current × Resistance

$V = I \times R$

Let’s work through an example.

A circuit has a current of $2$ amps and a resistance of $5$ ohms. To find the voltage, we plug those numbers into the formula:

$V = I \times R$

$V = 2 \times 5$

$V = 10$ volts

Sometimes you’ll be given the voltage and need to solve for current or resistance instead. You can rearrange Ohm’s Law to solve for any of the three variables:

$I = \frac{V}{R}$

$R = \frac{V}{I}$

To remember the rearrangements, use the triangle above: cover the letter you’re solving for, and the remaining letters give the formula.

Example: Metric prefixes

A $6$ V battery is connected across a $2$ kΩ resistor. What is the current?

$2$ kΩ $= 2, 000$ Ω

$I = \frac{V}{R} = \frac{6}{2 , 000} = 0.003$ A

Answer: $0.003$ A, which is $3$ mA

Knowledge check

If a circuit has a voltage of $12$ volts and a resistance of $4$ ohms, what is the current?

Solution:

(spoiler)

$3$ amps

Measuring instruments

Now that we’ve covered voltage, current, and resistance, let’s look at the tools used to measure them in a real circuit.

Voltmeter: measures voltage. A voltmeter is connected in parallel with a component of the circuit, since voltage is measured across two points.

Ammeter: measures current. Unlike a voltmeter, an ammeter must be connected in series with a component, since current has to flow through the meter to be measured.

Key points

Atomic structure & electricity basics

Atoms have electrons, neutrons, protons; electricity concerns electron movement
Two kinds of charge: positive (protons) and negative (electrons)
Neutral object: electrons balance protons, so no net charge; exchanging electrons creates net positive/negative objects (e.g., static shock)

Conductors, insulators & semiconductors

Conductor: allows electron flow easily (metals like copper, silver — used in wires)
Insulator: blocks electrical flow (rubber, glass, plastic — used for safety coatings)
Semiconductor: can act as either, depending on conditions (silicon — basis of transistors/microchips)

Ohm’s Law & circuit quantities

Voltage (V, Volts): electrical pressure pushing current, like water pressure
Current (I, Amps): flow of electric charge, like water flow rate
Resistance (R, Ohms Ω): opposition to current flow, like a narrow pipe
Ohm’s Law: $V = I \times R$ , with rearrangements $I = \frac{V}{R}$ and $R = \frac{V}{I}$
- Use the V/I/R triangle: cover the unknown variable to get the formula
Resistors limit current: fixed resistors (constant resistance) vs. variable resistors/potentiometers (adjustable, used in volume/dimmer controls)
Convert metric prefixes (milli = $0.001$ , kilo = $1, 000$ , mega = $1, 000, 000$ ) to base units before calculating

Measuring instruments

Voltmeter: measures voltage; connected in parallel
Ammeter: measures current; connected in series (current must flow through it)
Ohmmeter: measures resistance; sends its own current, so component must be disconnected from power
Multimeter: combines voltmeter, ammeter, and ohmmeter into one switchable device

Atomic structure

As we discussed in Chemistry, the atom contains $3$ parts: electrons, neutrons, and protons. In simplest terms, electricity is all about how electrons move.

Conductors, insulators & semiconductors

Conductor: a material that allows electrons to flow through it easily. Most metals, like copper and silver, are good conductors, which is why they’re used to make electrical wires.

Ohm’s law

A helpful way to picture voltage, current, and resistance is to imagine water flowing through a pipe.

Voltage: the electrical pressure that pushes electrical current through a wire, similar to the water pressure pushing water through a pipe. Voltage is measured in Volts (V).

Current: the flow of electric charge (electrons) through a wire, similar to the flow rate of water through a pipe. Current is measured in Amps (A).

Resistance: an object’s opposition to the flow of electrical current, similar to how a narrow pipe restricts the flow of water. Resistance is measured in Ohms (Ω).

Sidenote

Resistors

Resistors: A device meant to limit the flow of electric current

Fixed resistors: A device that has a fixed resistance. It will always present the same resistance to the circuit.

Ohm’s Law is the basis for electronics and describes the relationship between voltage, current, and resistance. It states that:

Voltage = Current × Resistance

$V = I \times R$

Let’s work through an example.

A circuit has a current of $2$ amps and a resistance of $5$ ohms. To find the voltage, we plug those numbers into the formula:

$V = I \times R$

$V = 2 \times 5$

$V = 10$ volts

Sometimes you’ll be given the voltage and need to solve for current or resistance instead. You can rearrange Ohm’s Law to solve for any of the three variables:

$I = \frac{V}{R}$

$R = \frac{V}{I}$

To remember the rearrangements, use the triangle above: cover the letter you’re solving for, and the remaining letters give the formula.

Example: Metric prefixes

A $6$ V battery is connected across a $2$ kΩ resistor. What is the current?

$2$ kΩ $= 2, 000$ Ω

$I = \frac{V}{R} = \frac{6}{2 , 000} = 0.003$ A

Answer: $0.003$ A, which is $3$ mA

Knowledge check

If a circuit has a voltage of $12$ volts and a resistance of $4$ ohms, what is the current?

Solution:

(spoiler)

$3$ amps

Measuring instruments

Now that we’ve covered voltage, current, and resistance, let’s look at the tools used to measure them in a real circuit.

Voltmeter: measures voltage. A voltmeter is connected in parallel with a component of the circuit, since voltage is measured across two points.

Ammeter: measures current. Unlike a voltmeter, an ammeter must be connected in series with a component, since current has to flow through the meter to be measured.