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TEC-ELEC48-09 · Lesson 1 · 18 clock hours · theory

ETA CET Domain Review: DC/AC Theory, Semiconductors, and Digital Electronics

Objective. Students will answer ETA CET practice questions across the DC/AC circuits, semiconductor devices, and digital electronics domains at a minimum 75% correct rate on a timed domain quiz.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by an industry-certified professional or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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ETA CET Domain Review: DC/AC Theory, Semiconductors, and Digital Electronics

The Electronics Technicians Association (ETA) International Certified Electronics Technician (CET) exam tests your ability to apply fundamental electronics principles to real-world troubleshooting and circuit analysis. This lesson reviews the three core domains that appear on the associate-level CET: DC/AC circuit theory, semiconductor devices, and digital electronics. Mastering these domains gives you the foundation you need to pass the exam and perform competently on the job.

DC Circuit Theory

Ohm's Law is the starting point for almost every circuit calculation: V = IR, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. Rearranged, I = V/R and R = V/I.

Kirchhoff's Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop equals zero. In practice this means the voltage drops across series components must add up to the source voltage.

Kirchhoff's Current Law (KCL) states that the total current entering any node equals the total current leaving that node. This governs how current splits in parallel branches.

Series circuits share the same current through every component; total resistance is the sum of individual resistances. Parallel circuits share the same voltage across every branch; total conductance is the sum of individual conductances, and total resistance is always less than the smallest branch resistance.

The voltage divider formula lets you find the voltage across one resistor in a series string: V_out = V_in × (R_out / R_total).

Power in a DC circuit is calculated as P = IV = I²R = V²/R, with the result in watts.

AC Circuit Theory

Alternating current reverses direction periodically. Frequency (f) is measured in hertz; period T = 1/f. Peak, peak-to-peak, and RMS values are all related; for a sine wave, V_RMS = V_peak × 0.707.

Capacitive reactance opposes changes in voltage: X_C = 1 / (2πfC). Inductive reactance opposes changes in current: X_L = 2πfL. Both are measured in ohms.

In RLC series circuits, impedance Z = √(R² + (X_L − X_C)²). At resonance, X_L = X_C, impedance is purely resistive and equals R, and current is at maximum.

Phase angle θ = arctan((X_L − X_C) / R). A positive angle means the circuit is inductive; negative means capacitive.

Semiconductor Devices

A diode conducts current in one direction only. The P-N junction requires a forward-bias voltage (approximately 0.6–0.7 V for silicon, approximately 0.2–0.3 V for germanium) before significant conduction occurs. In reverse bias, only a tiny leakage current flows until breakdown voltage is reached. Zener diodes are designed to operate in reverse breakdown for voltage regulation.

The bipolar junction transistor (BJT) has three regions: emitter, base, and collector. In the active region, collector current is approximately equal to the DC current gain (h_FE or β) multiplied by the base current: I_C = β × I_B. The transistor is cut off when base current is zero and saturated when the collector-to-emitter voltage approaches zero.

A field-effect transistor (FET) controls drain current with gate voltage rather than gate current, making it a voltage-controlled device with very high input impedance. JFETs and MOSFETs are the two main families.

Always observe ESD (electrostatic discharge) precautions when handling semiconductors. Wear a grounded wrist strap, use anti-static mats, and keep components in ESD-safe packaging until installation. ESD damage may not be immediately visible but can cause latent failures in the field.

Digital Electronics

Digital circuits operate on binary logic: HIGH (1) and LOW (0). The fundamental building blocks are logic gates.

| Gate | Function | Boolean expression |

|------|----------|--------------------------|

| AND | Output HIGH only when all inputs HIGH | Y = A · B |

| OR | Output HIGH when any input HIGH | Y = A + B |

| NOT (Inverter) | Output is complement of input | Y = Ā |

| NAND | AND followed by inversion | Y = A̅·̅B̅ |

| NOR | OR followed by inversion | Y = A̅+̅B̅ |

| XOR | Output HIGH when inputs differ | Y = A ⊕ B |

Truth tables list every possible input combination and the resulting output. You must be able to complete a truth table for any combination of basic gates.

De Morgan's theorems are essential for simplifying Boolean expressions and understanding NAND/NOR equivalents:

Number systems tested on the CET include binary, octal, hexadecimal, and decimal. Practice converting between them. Binary addition and the concept of two's complement for representing negative numbers also appear on the exam.

Study Strategy for This Lesson

Use the personal weakness map from the diagnostic quiz to focus your remaining study time. If your DC/AC score is below 70%, re-work calculation problems by hand before reaching for a calculator. If semiconductors are weak, drill device symbols and biasing conditions with flash cards. If digital logic is the gap, practice drawing truth tables for multi-gate circuits until the process is automatic. Every concept in this lesson has appeared in some form on the CET; none of it is background reading.

Key terms10

Ohm's LawThe relationship V = IR stating that voltage across a resistor equals current through it multiplied by its resistance; the foundation of DC circuit analysis.
Kirchhoff's Voltage Law (KVL)The rule that the algebraic sum of all voltages around any closed loop in a circuit equals zero.
Kirchhoff's Current Law (KCL)The rule that the total current entering a node equals the total current leaving that node.
ReactanceThe opposition to AC current offered by a capacitor (X_C = 1/2πfC) or inductor (X_L = 2πfL), measured in ohms.
Impedance (Z)The total opposition to AC current in a circuit, combining resistance and reactance: Z = √(R² + (X_L − X_C)²), measured in ohms.
Forward BiasThe condition in which a diode's P-type anode is connected to a more positive potential than its N-type cathode, allowing significant current to flow.
Beta (β / h_FE)The DC current gain of a BJT transistor; the ratio of collector current to base current (I_C / I_B) in the active region.
Truth TableA table listing every possible combination of logic gate inputs alongside the corresponding output, used to fully describe the behavior of a digital logic circuit.
De Morgan's TheoremsTwo Boolean algebra rules: (A·B)̄ = Ā+B̄ and (A+B)̄ = Ā·B̄, used to simplify logic expressions and find equivalent gate configurations.
ESD (Electrostatic Discharge)A sudden transfer of static electricity that can permanently damage semiconductor devices; controlled by grounded wrist straps, anti-static mats, and ESD-safe handling procedures.

Worked examples4

1. A series circuit has a 24 V source, R1 = 100 Ω, and R2 = 200 Ω. Find (a) the total current and (b) the voltage across R2.
  1. Find total resistance: R_total = R1 + R2 = 100 + 200 = 300 Ω
  2. Apply Ohm's Law for total current: I = V / R_total = 24 V / 300 Ω = 0.08 A (80 mA)
  3. Apply the voltage divider formula for R2: V_R2 = V_source × (R2 / R_total) = 24 × (200 / 300) = 24 × 0.667 = 16 V
  4. Verify with Ohm's Law: V_R2 = I × R2 = 0.08 A × 200 Ω = 16 V ✓
Answer: Total current = 80 mA; voltage across R2 = 16 V
2. An RLC series circuit has R = 30 Ω, X_L = 70 Ω, and X_C = 30 Ω, connected to a 120 V RMS source. Find (a) impedance and (b) circuit current.
  1. Find the net reactance: X_net = X_L − X_C = 70 − 30 = 40 Ω (inductive)
  2. Calculate impedance: Z = √(R² + X_net²) = √(30² + 40²) = √(900 + 1600) = √2500 = 50 Ω
  3. Apply Ohm's Law for AC: I = V / Z = 120 V / 50 Ω = 2.4 A RMS
Answer: Z = 50 Ω; I = 2.4 A RMS
3. A BJT in common-emitter configuration has a base current of 50 µA and a β (h_FE) of 120. Find the collector current.
  1. Recall the relationship: I_C = β × I_B
  2. Convert base current to amperes: I_B = 50 µA = 50 × 10⁻⁶ A = 0.000050 A
  3. Calculate: I_C = 120 × 0.000050 A = 0.006 A = 6 mA
Answer: Collector current I_C = 6 mA
4. Convert the binary number 1011 to its decimal equivalent.
  1. Write out the positional values for a 4-bit binary number (right to left): 2³, 2², 2¹, 2⁰ = 8, 4, 2, 1
  2. Multiply each bit by its positional value: 1×8 = 8, 0×4 = 0, 1×2 = 2, 1×1 = 1
  3. Sum the results: 8 + 0 + 2 + 1 = 11
Answer: Binary 1011 = Decimal 11

The math in this lesson2

Learners apply Ohm's law and the voltage-divider formula to find current and voltage in series circuits.
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Brush up in the math halls at newSchoolWorks.com:
In class: Instructor-led rapid-review lecture covering Ohm's Law, Kirchhoff's laws, RC/RL/RLC circuits, diode and transistor operation, and Boolean logic gates, with each concept immediately followed by two to four representative CET-style questions answered and explained as a group. · Students complete a 60-question, timed domain diagnostic (20 questions per domain) drawn from ETA CET practice question banks, then self-score and plot results on a personal weakness map that highlights which sub-topics need additional study. · Small-group study stations rotate through three tables—one per domain—where students quiz each other using printed flash cards, work through Ohm's Law and voltage-divider calculation drills, and trace logic-gate truth tables on whiteboards until every member scores 75% or better on a five-question spot check at each station.
Materials: ETA International CET Study Guide (current edition), ETA CET practice question bank (printed sets and/or ETA online practice portal), scientific calculators, whiteboard and markers, personal weakness-map worksheet, flash-card sets for semiconductor symbols and digital logic
Check: Timed 60-question domain diagnostic scored immediately; pass = 75% correct (45/60) overall with no single domain below 70%; students below threshold receive a written remediation plan before Lesson 2.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

ETA CET – DC Circuit Theory
1. Three resistors of 10 Ω, 20 Ω, and 30 Ω are connected in series across a 120 V source. What is the current flowing through the circuit?
ETA CET – DC Circuit Theory
2. In a parallel DC circuit, Kirchhoff's Current Law tells you that:
ETA CET – AC Circuit Theory
3. A series RLC circuit has R = 50 Ω, X_L = 90 Ω, and X_C = 50 Ω. What is the impedance of the circuit?
ETA CET – AC Circuit Theory
4. At resonance in a series RLC circuit, which of the following is true?
ETA CET – Semiconductor Devices
5. A silicon diode in a circuit has 0.5 V applied across it in the forward direction. What is its most likely operating state?
ETA CET – Semiconductor Devices
6. A BJT has a base current of 20 µA and a β of 150. What is the collector current?
ETA CET – Digital Electronics
7. Which Boolean expression correctly represents the output of a two-input NAND gate with inputs A and B?
ETA CET – Digital Electronics
8. According to De Morgan's theorem, the expression (A + B)̄ is equivalent to:
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