Question 1

Atomic structure review: Which subatomic particle inside an atom carries no net electrical charge?

Accepted Answer

Introduction / Context: Circuit behavior ultimately arises from atomic charges. Knowing which particles are charged or neutral helps explain conduction, insulation, and electrostatics in materials used for electrical engineering. Given Data / Assumptions: Standard atomic model with protons and neutrons in the nucleus, electrons in orbitals. Elementary charge magnitude denoted by e. No exotic particles or ions beyond this scope. Concept / Approach: Protons carry a positive charge of +e. Electrons carry a negative charge of −e and are mobile in conductors. Neutrons are electrically neutral, contributing mass and nuclear stability without contributing charge. Step-by-Step Solution: List particle charges: proton = +e, electron = −e, neutron = 0.Match to question: the one with zero charge is the neutron.Relate to materials: electron mobility in metals explains conductivity; neutral neutrons do not affect electric fields directly.Confirm selection: choose neutron. Verification / Alternative check: Textbook atomic tables show neutron with no net charge and mass slightly greater than proton, consistent with nuclear physics measurements. Why Other Options Are Wrong: Proton: positively charged; central to defining atomic number.Electron: negatively charged; principal charge carrier in metals.All of the above: incorrect because two of the three have nonzero charge. Common Pitfalls: Assuming neutrality means absence from interactions; neutrons influence nuclear stability but not electric fields.Confusing neutrality of atoms overall with neutrality of individual particles. Final Answer: Neutron

Question 2

Using a voltmeter correctly: How should a voltmeter be connected to measure the potential difference across a circuit element?

Accepted Answer

Introduction / Context: Correct instrument connection is essential for accurate measurements and safety. A voltmeter measures potential difference and must be connected without significantly altering the circuit operation. Given Data / Assumptions: Ideal voltmeter has very high internal resistance. Objective is to measure the voltage across a specific element. Avoid disturbing the current in the branch under test. Concept / Approach: Voltage is defined between two points. Therefore, the measuring instrument must be connected across those two points. High meter resistance minimizes current draw and measurement loading errors. Series connection would add resistance and change circuit currents, which is appropriate for an ammeter, not a voltmeter. Step-by-Step Solution: Identify the two nodes across which voltage is desired.Connect voltmeter leads across these nodes (parallel connection).Ensure meter internal resistance is large so that the meter current is negligible.Read the indicated potential difference without materially altering circuit behavior. Verification / Alternative check: Circuit simulations or lab practice show that a high-resistance parallel instrument leaves branch currents nearly unchanged while reporting the correct voltage drop. Why Other Options Are Wrong: Series connection: appropriate for ammeters, not voltmeters.Measure current or charge: instruments exist for those, but a voltmeter measures voltage. Common Pitfalls: Accidentally inserting a low-impedance meter across a source, causing a short.Confusing two-point voltage measurement with single-lead test methods that still reference a second node (ground). Final Answer: In parallel with the circuit or component under test

Question 3

Charge quantization: Which unit of electric charge corresponds to approximately 6.25 × 10^18 electrons?

Accepted Answer

Introduction / Context: Electric charge is quantized in multiples of the elementary charge carried by electrons and protons. Converting between a count of electrons and standard SI units helps relate microscopic particles to macroscopic measurements. Given Data / Assumptions: Elementary charge magnitude e ≈ 1.602 × 10^-19 coulomb per electron. Electron count given as about 6.25 × 10^18. Aim is to identify the corresponding SI unit name. Concept / Approach: Total charge Q equals number of electrons n multiplied by the elementary charge e, with a negative sign for electrons that is ignored for magnitude. Using approximate values leads to the definition of one coulomb. Step-by-Step Solution: Use relation: Q = n * e.Substitute n ≈ 6.25 × 10^18 and e ≈ 1.6 × 10^-19 C.Compute magnitude: Q ≈ (6.25 × 10^18) * (1.6 × 10^-19) C ≈ 1.0 C.Therefore the unit name for this quantity is the coulomb. Verification / Alternative check: By definition, 1 coulomb equals approximately 6.242 × 10^18 elementary charges; rounding explains the 6.25 figure commonly used in introductory problems. Why Other Options Are Wrong: Ampere: unit of current (charge per second), not charge itself.Volt: unit of electric potential difference.Joule: unit of energy. Common Pitfalls: Treating ampere and coulomb interchangeably; they measure different physical quantities.Forgetting the sign of electron charge; here only the magnitude is relevant. Final Answer: A coulomb

Question 4

Energy conversion: Which common voltage source converts chemical energy directly into electrical energy for use in circuits?

Accepted Answer

Introduction / Context: Electrical systems draw power from sources that convert a primary energy form into electricity. Recognizing the energy pathway is important for system design, safety, and maintenance planning. Given Data / Assumptions: The question asks for a voltage source that uses chemical reactions internally. Steady DC output is implied for typical small circuits. No external fuel feed is considered for the small source. Concept / Approach: A battery consists of one or more electrochemical cells where redox reactions at electrodes create an electromotive force. The chemical energy stored in active materials is directly converted into electrical energy as charge moves through an external circuit. Step-by-Step Solution: Identify conversion type: chemical → electrical.Select device: batteries perform this conversion internally using electrolyte and electrodes.Differentiate alternatives: solar cells convert radiant energy; generators convert mechanical energy; power supplies convert one form of electricity to another form.Conclude: battery is the correct choice. Verification / Alternative check: Discharge curves and cell reactions for alkaline, lead–acid, or lithium-ion chemistries confirm that electrical work arises from redox potentials between the two electrodes. Why Other Options Are Wrong: Solar cell: photovoltaic conversion of light, not chemical reactions in an electrolyte.Electronic power supply: converts AC to regulated DC; no primary chemical energy involved.Electrical generator: converts mechanical shaft power to electricity via electromagnetic induction. Common Pitfalls: Thinking any DC source must be a battery; many DC sources are power supplies or rectifiers.Confusing fuel cells with batteries; fuel cells also use chemistry but require continuous external fuel and oxidant feeds. Final Answer: Battery

Question 5

Temperature-sensitive resistive devices: Which component is deliberately designed so its resistance varies strongly with temperature?

Accepted Answer

Introduction / Context: Sensors that translate physical variables into electrical signals are essential in control and measurement. For temperature, designers often use components whose resistance changes predictably with temperature to build simple, accurate measurement circuits. Given Data / Assumptions: We are considering resistive components commonly found in basic circuits. Goal is to identify the one engineered for temperature dependence as its primary function. Both negative and positive temperature coefficients may exist. Concept / Approach: Thermistors are semiconductor resistors with a large temperature coefficient of resistance. NTC thermistors decrease resistance as temperature rises, while PTC types increase resistance. Their strong sensitivity enables compact thermometry and protection functions. Step-by-Step Solution: Define thermistor: a resistor optimized for temperature sensitivity.Contrast with potentiometer: a three-terminal adjustable divider for setting voltage; not inherently temperature sensitive by design.Contrast with rheostat: a two-terminal variable resistor for current control; again, not intended as a temperature sensor.Contrast with photoconductive cell: resistance varies with light intensity, not temperature.Therefore choose thermistor. Verification / Alternative check: Datasheets specify beta constants or temperature coefficients for thermistors, confirming their role in temperature measurement and inrush current limiting. Why Other Options Are Wrong: Potentiometer: manual adjustment; temperature dependence is an error term, not the feature.Rheostat: variable resistor for power control, not temperature sensing.Photoconductive cell: light-dependent resistor; senses illumination, not heat. Common Pitfalls: Assuming all resistors vary with temperature significantly; standard resistors aim for low temperature coefficient.Confusing thermistor behavior with RTDs; RTDs use metals with small, linear coefficients, while thermistors are semiconductors with larger, nonlinear response. Final Answer: Thermistor

Question 6

Basic electrical quantities — which term designates “electrical pressure”? In introductory electrical engineering, the term used to describe the driving force that pushes charge through a circuit (often called electrical pressure) is:

Accepted Answer

Introduction / Context: In circuit theory and practical electronics, technicians and students often hear the phrase “electrical pressure.” This colloquial term refers to the potential difference that drives electrons through a conductive path. Identifying the correct formal term helps build a precise vocabulary for analyzing and troubleshooting circuits. Given Data / Assumptions: The prompt asks for the correct technical name for electrical pressure. No numerical computation is required. Standard electrical quantities considered: voltage, current, resistance, conductance. Concept / Approach: Electrical pressure is an intuitive analogy to fluid pressure. Just as fluid pressure drives fluid flow, electric potential difference drives electric current. The standard term for electric potential difference is voltage, measured in volts. Current is the rate of charge flow (amperes). Resistance is the opposition to current (ohms). Conductance is the reciprocal of resistance (siemens). Step-by-Step Solution: Map the analogy: pressure (fluid) ↔ potential difference (electrical).Identify the formal term for potential difference: voltage.Confirm that current, resistance, and conductance are different fundamental quantities.Select ‘‘voltage’’ as the correct description of electrical pressure. Verification / Alternative check: Ohm’s law states V = I * R. Here V (voltage) is the driving force; if voltage increases across a given resistance, current increases proportionally, mirroring how higher pressure increases fluid flow through a restriction. Why Other Options Are Wrong: Current: measures charge flow, not the force driving it. Resistance: opposes current, analogous to a flow restriction. Conductance: the ease of current flow; the inverse of resistance. Common Pitfalls: Confusing “voltage” with “current” because both are often discussed together; remember voltage causes current through resistance. Assuming resistance or conductance can “push” current; they only determine how much current flows for a given voltage. Final Answer: voltage

Voltage and Current Questions