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NCCER Module 26103-20: Introduction to Electrical Circuits COMPREHENSIVE STUDY SHEET WITH Q&A AND EXPLANATIONS SECTION 1: ATOMIC THEORY & ELECTRICAL FUNDAMENTALS Q1: What is the smallest unit of matter? A: Atoms Q2: A proton repels a(n) ______. A: Another proton (like charges repel) Q3: An electron repels a(n) ______. A: Another electron (like charges repel) Q4: A proton (+) ______ an electron (-). A: Attracts (opposite charges attract) Q5: What are the three subatomic particles in an atom? A: Protons (positive charge), Neutrons (no charge), and Electrons (negative charge) Q6: Where are protons and neutrons located? A: In the nucleus (center) of the atom Q7: What determines an atom's chemical and electrical properties? A: The number of valence electrons (electrons in the outer shell) Q8: An atom with seven valence electrons is most likely a(n) ______. A: Insulator (5 or more valence electrons = insulator) Q9: An atom with four valence electrons is a ______. A: Semiconductor Q10: What are examples of good semiconductors? A: Silicon and Germanium Q11: Materials with electrical characteristics that fall between insulators and conductors are ______. A: Semiconductors Q12: Is copper a conductor or insulator? A: Conductor (allows electrons to flow easily) Q13: The negative terminal of a battery contains a large reserve of free ______. A: Electrons SECTION 2: ELECTRICAL UNITS & MEASUREMENTS
Q14: What is voltage? A: The driving force that makes current flow in a circuit. Also called electromotive force (EMF), difference of potential, or electrical pressure. Q15: Voltage is defined as the ______. A: Difference of potential Q16: What is the unit of measurement for voltage? A: Volts (V) Q17: What is current? A: The flow of electrons in a circuit Q18: What is the unit of measurement for current? A: Amperes (A) Q19: What is resistance? A: An electrical property that opposes the flow of current through a circuit Q20: What is the unit of measurement for resistance? A: Ohms (Ω) Q21: What is power? A: The rate of doing work, or the rate at which energy is used or dissipated Q22: What is the unit of measurement for power? A: Watts (W) Q23: Coulombs are a measure of ______. A: Electric Charge (1 coulomb = 6.25 × 10¹⁸ electrons) Q24: What does the prefix "Mega" mean? A: 1 million (example: 1 megawatt = 1,000,000 watts) Q25: A measurement of 1,000 mils is equal to ______. A: 1 inch SECTION 3: OHM'S LAW (CRITICAL FOR CALCULATIONS) Formula: V = I × R V = Voltage (Volts) I = Current (Amperes) R = Resistance (Ohms) Rearranged formulas: I = V ÷ R R = V ÷ I
Q30: If the voltage source is 140V and the resistance is 2 ohms, how many amps are in the current? A: 70A EXPLANATION: Given: V = 140V, R = 2Ω Use formula: I = V ÷ R I = 140V ÷ 2Ω = 70A SECTION 4: POWER EQUATIONS (CRITICAL FOR CALCULATIONS) Power Formulas: P = V × I (Power = Voltage × Current) P = I² × R (Power = Current² × Resistance) P = V² ÷ R (Power = Voltage² ÷ Resistance) PRACTICE PROBLEMS WITH EXPLANATIONS: Q31: A circuit has a source voltage of 120V and a current of 10A. What is the power in watts? A: 1,200W EXPLANATION: Given: V = 120V, I = 10A Use formula: P = V × I P = 120V × 10A = 1,200W Q32: If the resistance of a circuit is 20 ohms and the current is 15 amps, what is the power in watts? A: 4,500W EXPLANATION: Given: R = 20Ω, I = 15A Use formula: P = I² × R P = (15A)² × 20Ω P = 225 × 20 = 4,500W
SECTION 5: SERIES CIRCUITS
Q33: What is a series circuit? A: A circuit that provides only one path for current flow Q34: In a series circuit, how do you calculate total resistance? A: Total resistance equals the sum of all individual resistances Formula: R_total = R₁ + R₂ + R₃ + ... Q35: If a series circuit has two 30-ohm loads, what is the total resistance? A: 60 ohms EXPLANATION: Given: R₁ = 30Ω, R₂ = 30Ω R_total = R₁ + R₂ R_total = 30Ω + 30Ω = 60Ω Q36: In a series circuit, the current is ______ through all loads. A: The same Q37: In a series circuit, voltage is ______. A: Divided across the loads (voltage divider) SECTION 6: PARALLEL CIRCUITS Q38: What is a parallel circuit? A: A circuit where each load is connected directly to the voltage source, providing multiple paths for current flow Q39: In a parallel circuit, the voltage drop ______. A: Is the same across all loads Q40: In a parallel circuit, current is ______. A: Divided between the loads (current divider) Q41: A 10-ohm resistor and a 15-ohm resistor are connected in parallel. What is the total resistance? A: 6 ohms EXPLANATION: For parallel circuits: 1/R_total = 1/R₁ + 1/R₂ 1/R_total = 1/10 + 1/ 1/R_total = 3/30 + 2/30 = 5/ R_total = 30/5 = 6Ω ALTERNATE METHOD (for 2 resistors):
Q52: What are relays? A: Electromechanical devices consisting of a coil and one or more sets of contacts, used as a switching device SECTION 9: ELECTRICAL DEVICES & COMPONENTS Q53: An electrical device that operates by chemically creating a potential difference between two points is a ______. A: Battery Q54: What is a battery? A: A DC voltage source consisting of two or more cells that convert chemical energy into electrical energy Q55: What is used to step voltage up for transmission? A: Transformer Q56: What is voltage drop? A: The change in voltage across a component caused by current flowing through it and the resistance opposing it SECTION 10: MEASUREMENT INSTRUMENTS Q57: Resistance is measured using a(n) ______. A: Ohmmeter Q58: What is a voltmeter? A: An instrument for measuring voltage where the resistance is fixed Q59: How is current measured with an in-line type meter? A: The meter is connected in series with the circuit (the circuit must be opened and the meter inserted) Q60: What is the most common type of test meter used by electricians? A: Volt-Ohm-Milliammeter (VOM), also called a Multimeter Q61: To make sure voltage is turned off before touching terminals, use a ______. A: Voltage tester SECTION 11: ELECTRICAL CIRCUITS & COMPONENTS Q62: An electrical circuit contains, at minimum, how many components? A: 3 components: voltage source, a load, and conductors (wires). Should also have a means to control current (switch). Q63: What is a circuit? A: A complete path for current flow
Q64: What is a conductor? A: A material that allows electric charges to flow through it easily Q65: What is an insulator? A: A material that does not allow electricity to move through it easily Q66: What is a series-parallel circuit? A: A hybrid arrangement containing both series and parallel connections SECTION 12: POWER GENERATION & DISTRIBUTION Q67: Where does electricity come from? A: Electrical generating plants operated by utilities, using steam from coal-burning or nuclear power plants to power turbines Q68: The voltage used by a typical television or toaster is ______. A: 120V Q69: Electrical power traveling through long-distance transmission lines may be as high as ______. A: 750,000V (750kV) Q70: What voltage do you typically receive at home? A: About 120V (or 240V for larger appliances) SECTION 13: WIRE CHARACTERISTICS Q71: What factors affect wire resistance? A: Length, cross-sectional area, material, and temperature Q72: A mil equals ______ inch. A: 0.001 inch (one-thousandth) Q73: What is a circular mil? A: The cross-sectional area of a wire one mil in diameter Q74: How does wire length affect resistance? A: Resistance is directly proportional to length (longer wire = more resistance) Q75: How does wire cross-sectional area affect resistance? A: Resistance is inversely proportional to cross-sectional area (thicker wire = less resistance) SECTION 14: COULOMB'S LAW Q76: What can Coulomb's law be used to calculate? A: The force between two charges
