Electronic Components (Chapter 2)

These question-and-answer flashcards cover key concepts from wire and cable basics through passive electronic components such as resistors, capacitors, coils, and transformers, including safety precautions, formulas, and practical applications.

What is the primary purpose of electrical wire?

To carry an electrical current from one point to another.

How does solid wire differ from stranded wire?

Solid wire is a single conductor, while stranded wire contains two or more twisted or braided conductors.

Why is copper commonly used for wiring?

Because it is a low-resistance metal that conducts electricity well.

What is tinned wire and why is it useful?

Wire whose copper strands are coated with tin; the coating makes the wire easier to solder.

How does a cable differ from ordinary wire?

A cable has one or more conductors and more insulation than ordinary wire.

What type of cable is designed to carry high-frequency signals such as television?

Coaxial cable.

What safety action should be taken if a wire feels hot to the touch?

Use a heavier-gauge wire or reduce the current, because the wire is carrying too much current.

What is the function of a mechanical switch?

To permit or interrupt the flow of current to various points in a circuit.

Define an SPST switch.

Single-Pole, Single-Throw—a basic on/off switch controlling one circuit path.

Define an SPDT switch.

Single-Pole, Double-Throw—one input can be connected to one of two outputs.

Define a DPST switch.

Double-Pole, Single-Throw—simultaneously switches two separate circuits on or off.

Define a DPDT switch.

Double-Pole, Double-Throw—two inputs can each connect to one of two outputs.

What are NO and NC in a push-button switch?

Normally Open (contacts open until pressed) and Normally Closed (contacts closed until pressed).

How does a rotary switch operate?

A wafer-like switch where a rotating shaft connects a pole to two or more contacts; wafers can be stacked for more poles.

What closes the contacts in a mercury switch?

A blob of mercury that moves with position, completing the circuit.

What is a relay?

An electromagnetic switch where current through a coil moves contacts to open or close another circuit.

Describe a reed switch relay.

A glass-enclosed pair of contacts that close when exposed to a magnetic field, forming a simple SPST relay.

What principle does a moving-coil meter use?

A coil on a pivot rotates between magnetic poles when current passes through it.

What is the basic function of a microphone?

To convert sound waves into corresponding variations in electrical current.

How does a carbon microphone work?

Diaphragm motion changes pressure on carbon particles, varying resistance and producing a signal.

How does a dynamic microphone generate a signal?

A small coil attached to the diaphragm moves through a magnetic field, inducing a proportional current.

How does a condenser (capacitor) microphone operate?

Diaphragm movement changes the spacing between two plates, altering capacitance and producing a signal.

How does a crystal microphone create voltage?

Sound bends a piezoelectric wafer, generating a proportional voltage.

What is the function of a speaker?

To convert variations in current or voltage into sound waves.

Why can a magnetic speaker be used as a microphone?

Because its operation is the reverse of a dynamic microphone; coil motion in a magnetic field can generate current.

State the primary purpose of a resistor.

To limit or resist the flow of current in a circuit.

What is a carbon-composition resistor?

A resistor made from powdered carbon blended with a binder; resistance varies with the carbon-to-binder ratio.

How can you create a DIY resistor with a pencil?

Draw a thick graphite line on paper; its resistance can be measured between two probe points.

What do the first three color bands on a resistor indicate?

First digit, second digit, and multiplier for the resistance value.

What do gold, silver, and no fourth band represent for tolerance?

Gold ±5 %, Silver ±10 %, None ±20 % tolerance.

What resistance does yellow-violet-red indicate?

47 × 100 Ω = 4700 Ω (4.7 kΩ) with the specified tolerance.

May you substitute a 6800 Ω resistor for a required 6700 Ω one?

Yes, values within the stated 10–20 % tolerance are usually acceptable.

What is the formula for total resistance in series?

RT = R1 + R2 + …

What is the formula for two resistors in parallel?

RT = (R1 × R2) / (R1 + R2).

Write the parallel formula for three or more resistors.

1/RT = 1/R1 + 1/R2 + 1/R3 + …

State the voltage divider equation.

Vout = Vin × (R2 / (R1 + R2)).

Why must resistor power rating be considered?

High current can overheat a resistor; using the correct wattage prevents damage and hazards.

What does the suffix k mean in resistor values such as 47 k?

× 1000 ohms; 47 k = 47,000 Ω.

What does the suffix M mean in resistor values such as 10 M?

× 1,000,000 ohms; 10 M = 10,000,000 Ω.

What is a metal-film resistor?

A resistor using a thin metal film to achieve precise resistance.

Describe a carbon-film resistor.

A ceramic cylinder coated with carbon film; a spiral groove sets the resistance length.

Why are wire-wound resistors special?

They are very accurate, handle high power, and are made by winding resistance wire on a form.

How does a photoresistor behave when light increases?

Its resistance decreases as light intensity rises.

What is a thermistor?

A temperature-sensitive resistor whose resistance usually decreases as temperature increases.

What is another name for a variable resistor?

Potentiometer; small adjustable versions are called trimmers.

What is the fundamental role of a capacitor?

To store electric charge (electrons) between two conductors separated by a dielectric.

Name three possible dielectric materials for capacitors.

Paper, ceramic, and plastic film (others include mica, glass, air, vacuum).

What is the SI unit of capacitance?

The farad (F).

Express 1 µF and 1 pF in farads.

1 µF = 1 × 10⁻⁶ F; 1 pF = 1 × 10⁻¹² F.

How can charging time be slowed for a capacitor?

Insert a resistor in series with the capacitor and the voltage source.

What is the total capacitance of capacitors in parallel?

CT = C1 + C2 + …

What is the total capacitance of two capacitors in series?

CT = (C1 × C2) / (C1 + C2).

Why must a capacitor’s voltage rating be observed?

Exceeding it can break down the dielectric and destroy the capacitor.

For what purpose are variable capacitors commonly used?

Tuning radio receivers, transmitters, and oscillators.

Why are electrolytic capacitors polarized?

Their oxide dielectric forms correctly only when the positive lead is at the most positive point in the circuit.

What safety warning applies to large capacitors?

They can store dangerous charges long after power is removed; never touch their leads without discharging them.

Define the RC time constant.

The time for a charging or discharging capacitor to change by 63.3 % of the total voltage change, equal to R × C seconds.

What does an RC integrator do to an input pulse train?

Produces a ramp (sawtooth) output, acting as a low-pass filter that favors lower frequencies.

What does an RC differentiator output?

Sharp, symmetrical positive and negative spikes corresponding to rapid input changes.

Design rule for RC integrators/differentiators?

RC should be at least 10 × the interval between input pulses or cycles.

How does a capacitor act in a power-supply filter?

It smooths the pulsating DC, reducing ripple to produce steadier output.

How does a small 0.1 µF capacitor remove digital power spikes?

It supplies transient current like a tiny battery, eliminating voltage glitches.

What magnetic effect occurs around a current-carrying wire?

An electromagnetic field encircles the wire.

How do coils (inductors) react to rapid current changes?

They resist rapid changes but pass steady (DC) current easily.

What is a transformer’s primary and secondary?

The input winding is the primary; the output winding is the secondary.

Why can transformers change voltage but not power?

Power is conserved; increasing voltage decreases current and vice versa.

How does turns ratio relate to transformer voltage?

Secondary voltage / Primary voltage = Secondary turns / Primary turns.

What is the purpose of an isolation transformer?

1 : 1 ratio to transfer power while electrically isolating circuits for safety.

Give an example of a step-up transformer ratio and effect.

1 : 5 turns boosts 5 V at the primary to 25 V at the secondary.

Give an example of a step-down transformer ratio and effect.

5 : 1 turns reduces 25 V at the primary to 5 V at the secondary.

List four common transformer types and uses.

Isolation, Power Conversion, High-Voltage (ignition, CRT), and Audio impedance matching.

What is the function of a choke in a circuit?

To limit or suppress fluctuating signals while allowing steady current to pass.

Why can interrupting current through a coil be dangerous?

It can generate a high-voltage pulse across the coil (inductive kickback).