Question 1

In a constant-voltage DC circuit, if the resistance value increases while the supply voltage remains unchanged, what happens to the circuit current according to Ohm's law?

Accepted Answer

Introduction: Ohm's law is the foundational relationship linking voltage, current, and resistance in DC circuits. This question checks whether you can qualitatively predict how current changes when resistance changes while the applied voltage is kept constant. Given Data / Assumptions: Ideal DC source with fixed voltage (constant V). Single effective resistance R in the path of current. Temperature and other secondary effects are neglected so R is constant except for the stated change. Concept / Approach: Ohm's law states I = V / R. With V fixed, current I is inversely proportional to R. Therefore, if R increases, the denominator grows and I must decrease in direct proportion. This inverse relationship underpins many circuit design decisions, such as selecting resistors to set bias currents or limiting current to safe values. Step-by-Step Solution: 1) Start from Ohm's law: I = V / R.2) Treat V as a constant because the source is fixed.3) Increase R to a higher value R'.4) Since the denominator increased, the fraction V / R' is smaller than V / R.5) Therefore, the current decreases when resistance increases at constant voltage. Verification / Alternative check: Use a numeric example: if V = 10 V and R changes from 100 Ω to 200 Ω, current changes from 0.1 A to 0.05 A. The current halves as the resistance doubles, exactly matching I ∝ 1/R. Why Other Options Are Wrong: Increase: contradicts I = V / R when V is constant. Stay the same: would only occur if R did not change or V changed proportionally. Not enough information: the law fully determines the outcome with V fixed and R increased. Oscillate: describes AC or time-varying phenomena, not a DC steady-state relationship. Common Pitfalls: Confusing cause and effect (thinking current controls voltage) or forgetting that resistance sets current for a given fixed voltage. Ensure units are consistent and remember the inverse proportionality. Final Answer: decrease

Question 2

Using Ohm's law, what electromotive force (voltage) is required to drive a current of 20 A through a 500 Ω resistor (assume steady DC conditions)?

Accepted Answer

Introduction: This is a direct application of Ohm's law to determine the voltage required for a specified current through a known resistance. Such calculations are common in sizing power supplies and checking feasibility in high-resistance or high-current paths. Given Data / Assumptions: Current I = 20 A (DC). Resistance R = 500 Ω. Ideal source and resistor; temperature effects neglected. Concept / Approach: Ohm's law states V = I * R. With the current and resistance provided, compute the voltage directly. The magnitude here will be large because both I and R are sizable, highlighting the power implications in practical designs. Step-by-Step Solution: 1) Write the formula: V = I * R.2) Substitute values: V = 20 A * 500 Ω.3) Multiply: V = 10,000 V.4) State the result clearly with units: 10,000 volts (10 kV). Verification / Alternative check: Power check: P = V * I = 10,000 * 20 = 200,000 W (200 kW). This confirms that such a condition implies enormous power dissipation in the resistor and is impractical without special hardware, reinforcing that the arithmetic is consistent. Why Other Options Are Wrong: 0.04 V, 2.5 V, 25.0 V, 100 V: All are orders of magnitude smaller than required by V = I * R for 20 A through 500 Ω. Common Pitfalls: Mixing units (kΩ vs Ω or mA vs A) and forgetting that large currents through large resistances require very high voltages. Always use base SI units when in doubt. Final Answer: 10,000 V

Question 3

A 40 W electric lamp is left ON continuously for 1,750 h. What is the total energy consumed, expressed in kilowatt-hours (kWh)?

Accepted Answer

Introduction: Electric energy billing commonly uses the kilowatt-hour (kWh) unit. Converting power and operating time to energy is a routine calculation for estimating electricity usage and costs. Given Data / Assumptions: Lamp power P = 40 W. Operating time t = 1,750 h. Constant power draw over the interval. Concept / Approach: Energy E = P * t. Convert the product to kWh by expressing power in kilowatts. 1 kW = 1,000 W and 1 kWh = energy used by 1 kW over 1 hour. Step-by-Step Solution: 1) Convert power to kilowatts: 40 W = 0.040 kW.2) Multiply by time: E = 0.040 kW * 1,750 h.3) Compute: E = 70 kWh.4) Present result with proper unit: 70 kWh. Verification / Alternative check: Compute in watt-hours first: E = 40 W * 1,750 h = 70,000 Wh. Convert Wh to kWh by dividing by 1,000: 70,000 Wh / 1,000 = 70 kWh, matching the above. Why Other Options Are Wrong: 43.75: Would correspond to 25 W or shorter time; does not match the given numbers. 43,750 and 70,000: These are Wh, not kWh (missing the divide-by-1,000 step). 7: Off by a factor of 10; likely a unit slip. Common Pitfalls: Forgetting to convert watts to kilowatts or interpreting Wh as kWh. Always check unit consistency: multiply kW by hours to get kWh. Final Answer: 70

Question 4

In electronics troubleshooting, the term "half-splitting" refers to which systematic diagnostic method when locating a fault in a circuit or system?

Accepted Answer

Introduction: Efficient troubleshooting relies on structured search strategies. Half-splitting is a classic technique used by technicians to quickly narrow down the location of a fault in complex circuits and systems. Given Data / Assumptions: System or circuit exhibits abnormal behavior or failure. You have access to measurement points along the signal or power path. The system can be tested safely while powered or stimulated. Concept / Approach: Half-splitting divides the suspected path or subsystem roughly in half, tests at that midpoint, and then chooses the half that contains the fault. Repeating this divide-and-test process rapidly converges on the faulty stage or interconnection, similar to a binary search. Step-by-Step Solution: 1) Identify the input and output (or start and end) of the suspect path.2) Select a middle checkpoint and measure the expected signal/voltage there.3) If the measurement is correct at mid-point, the fault lies downstream; if incorrect, the fault lies upstream.4) Repeat by splitting the faulty half again and retesting until the exact component or connection is found. Verification / Alternative check: Compare with a working reference unit or schematic values. The half-splitting process should converge in log2(N) steps for N checkpoints, providing a fast path to the fault compared with random probing. Why Other Options Are Wrong: Nuclear fuel cells: unrelated to troubleshooting methods. Reducing AC to low DC: describes rectification/transformers, not diagnostics. Limiting current: describes protective components like resistors or fuses. Boosting RF gain by 3 dB: a performance change, not a fault-location strategy. Common Pitfalls: Skipping documentation and randomly probing points wastes time. Without a clear path definition, half-splitting loses its efficiency. Always isolate power safely and account for intermittent faults. Final Answer: a means of isolating a problem in a circuit

Question 5

In elementary physics and electrical engineering, energy is commonly defined as the ability to do work or to produce observable effects. Which option best aligns with this definition?

Accepted Answer

Introduction: Energy underpins all physical processes. In engineering contexts, energy can transform into different forms, creating effects such as heating, lighting, and acoustic vibrations. This question probes conceptual understanding of energy's manifestations. Given Data / Assumptions: Standard textbook definition: energy is the capacity to do work or to produce heat. Real systems convert energy between forms (electrical, thermal, radiant, acoustic, mechanical). No specific numeric computation is required. Concept / Approach: If a system has energy and interacts with its environment, it can generate various measurable outcomes. Electrical energy can heat a resistor (Joule heating), power a lamp to emit light (radiant energy), or drive a loudspeaker to produce sound (mechanical/acoustic energy). Therefore, multiple listed effects are valid manifestations of energy. Step-by-Step Reasoning: 1) Start from the broad definition: energy enables work or heat production.2) Map to effects: work/heat can appear as temperature rise, light emission, or mechanical vibrations.3) Recognize conversions: electrical → thermal (I^2 * R), electrical → radiant (LED filament), electrical → mechanical → acoustic (speaker).4) Therefore, any of the listed effects can result from energy expenditure. Verification / Alternative check: Conservation of energy guarantees that input energy equals the sum of outputs plus losses. Observing heat, light, or sound confirms energy transfer and conversion have occurred. Why Other Options Are Wrong: Produce heat, light, or sound (individually): each is correct but incomplete versus the comprehensive set. None of these: contradicts the fundamental definition and common observations. Common Pitfalls: Equating energy solely with electrical energy, or forgetting that energy can neither be created nor destroyed but only converted. Real devices often produce multiple effects simultaneously (e.g., lamps also produce heat). Final Answer: All of the above

Question 6

In battery specifications, which unit is standard for rating a battery’s capacity to deliver charge over time (commonly at a specified discharge rate)?

Accepted Answer

Introduction: Battery datasheets present several ratings, including capacity, energy, and voltage. Distinguishing between ampere-hours (Ah) and watt-hours (Wh) is critical for selecting and comparing batteries in electronics and power systems. Given Data / Assumptions: Conventional consumer and industrial battery ratings. Capacity is defined as total charge deliverable at a specified rate and temperature. Energy is a separate quantity derived from voltage and capacity. Concept / Approach: Battery capacity measures charge, not energy. The standard unit for capacity is ampere-hour: 1 Ah means the battery can ideally provide 1 A for 1 hour (or 0.5 A for 2 hours, etc.), subject to discharge-rate effects (Peukert's law) and temperature. Energy in watt-hours equals nominal voltage times capacity (Wh = V_nom * Ah). Step-by-Step Clarification: 1) Identify the sought quantity: capacity (charge over time).2) Match to units: current * time = ampere-hour (Ah).3) Differentiate from energy: energy uses watt-hour (Wh) or kilowatt-hour (kWh).4) Conclude that the correct unit for capacity is Ah. Verification / Alternative check: Check common cells: e.g., a 2,500 mAh (2.5 Ah) Li-ion 18650 cell at ~3.6 V has energy ≈ 2.5 Ah * 3.6 V = 9 Wh; this confirms the distinct roles of Ah and Wh. Why Other Options Are Wrong: kWh and Wh: units of energy, not charge capacity. Vh: voltage-time has no standard meaning for capacity. A/s: ampere per second is a rate-of-change of current, not capacity. Common Pitfalls: Confusing capacity (Ah) with energy (Wh). Always consider both capacity and nominal voltage when estimating runtime in watt-hours. Final Answer: Ah

Question 7

For a fixed resistance R, if the applied voltage across it is increased by a factor of five (steady DC), by what factor does the current change?

Accepted Answer

Introduction: Understanding proportionality in Ohm's law enables quick mental calculations in circuit design and testing. This question tests the ability to scale current when voltage is scaled with resistance held constant. Given Data / Assumptions: Fixed resistance R (constant with voltage and temperature). DC operation with a constant-voltage source. No additional reactive components. Concept / Approach: Ohm's law: I = V / R. With R fixed, current is directly proportional to voltage. Therefore, scaling V by a factor k scales I by the same factor k. Here k = 5, so current increases fivefold. Step-by-Step Solution: 1) Original current: I1 = V1 / R.2) New voltage: V2 = 5 * V1.3) New current: I2 = V2 / R = (5 * V1) / R = 5 * (V1 / R) = 5 * I1.4) Therefore, current increases by factor 5. Verification / Alternative check: Example numbers: R = 10 Ω, V1 = 2 V → I1 = 0.2 A. Increase voltage to 10 V → I2 = 1 A, which is 5 times larger. Why Other Options Are Wrong: Decreases fivefold: contradicts direct proportionality. Stays the same or not enough information: Ohm's law determines the result fully. Increases by 25: would be true for quantities proportional to V^2 (power), not current. Common Pitfalls: Mixing up current with power. Power P = V * I = V^2 / R grows with the square of voltage, but current grows linearly with voltage when R is fixed. Final Answer: It increases by a factor of five.

Question 8

For a fixed resistor R, if the current through it is halved in steady DC operation, what must happen to the voltage across the resistor (assume R remains constant)?

Accepted Answer

Introduction: This question probes proportional reasoning with Ohm's law when resistance is fixed. It is common in bias network design and troubleshooting where current changes must be related to voltage changes across a known resistor. Given Data / Assumptions: DC steady state. Resistor value R is constant (no temperature drift considered). Current is reduced to half its original value. Concept / Approach: Ohm's law gives V = I * R. With R constant, voltage is directly proportional to current. Therefore, halving current halves the voltage across the resistor as well. Step-by-Step Solution: 1) Original voltage: V1 = I1 * R.2) New current: I2 = I1 / 2.3) New voltage: V2 = I2 * R = (I1 / 2) * R = V1 / 2.4) Hence, the voltage across the resistor is halved. Verification / Alternative check: Numeric example: R = 100 Ω, I1 = 100 mA → V1 = 10 V. If I2 = 50 mA, V2 = 5 V, precisely half. Why Other Options Are Wrong: The resistance is halved: contradicts the assumption of fixed R. The voltage doubles: opposite of direct proportionality under constant R. None of the above: incorrect because the correct relation is explicit. Power halved but voltage unchanged: power P = V * I would not behave this way if V were unchanged while I halves (that would halve power, but then V would not satisfy V = I * R). Common Pitfalls: Mistaking proportionality: with constant R, V tracks I. Do not confuse with cases where the source voltage is fixed and current changes because R changes. Final Answer: the voltage is halved

Question 9

In regulated power supplies used in electronics, the regulator's job is to prevent the DC output voltage from drifting when there are changes in the AC line voltage (mains variations) and/or changes in the load current drawn by the connected circuit…

Accepted Answer

Introduction: Regulated power supplies are designed to provide a stable DC output even when the input conditions or the load conditions vary. This question tests understanding of two primary disturbances: fluctuations in the AC mains (line regulation) and changes in the load current (load regulation). Given Data / Assumptions: Output required: steady DC voltage for electronic circuits. Disturbances: AC line variations and load current changes. Typical regulator types: linear (series, shunt) and switch-mode (buck, boost, etc.). Concept / Approach: Line regulation measures how much the output changes when the input (line) voltage changes. Load regulation measures how much the output changes as load current varies from minimum to maximum. A good regulator minimizes both, maintaining a nearly constant output voltage under real-world conditions. Step-by-Step Solution: Identify disturbances: input (line) and output (load) changes.Define line regulation: ΔV_out per ΔV_in should be small.Define load regulation: ΔV_out per ΔI_load should be small.Regulated supplies implement feedback to correct deviations caused by either disturbance. Verification / Alternative check: Datasheets specify both line regulation (e.g., mV/V) and load regulation (e.g., mV/A or % from no-load to full-load); high-quality supplies exhibit tight figures in both metrics, proving that regulation targets both mains and load changes. Why Other Options Are Wrong: line voltage: Incomplete; ignores load changes. supply load: Incomplete; ignores line variations. frequency: Frequency tolerance alone is not the main regulation target. temperature only: Temperature affects drift but is not the principal definition of regulation here. Common Pitfalls: Confusing ripple reduction (filtering) with regulation (feedback control). Assuming only line changes matter; load transients are equally important. Final Answer: both line voltage and supply load

Question 10

A damaged resistor in practical electronics troubleshooting may show which observable or measurable characteristics?

Accepted Answer

Introduction: Recognizing signs of resistor failure is essential for effective troubleshooting. Resistors can fail open, drift in value, or show visible damage depending on how they were stressed (overpower, surge, overheating). Given Data / Assumptions: Through-hole or surface-mount resistors in typical low-voltage circuits. Possible stressors: overcurrent, overvoltage, thermal cycling, environmental factors. Technician has access to visual inspection and an ohmmeter. Concept / Approach: Failure modes include visual signs (discoloration, cracking, burn marks) and electrical changes (value drift upward due to film damage or open-circuit). An ohmmeter measurement (with power removed and at least one lead isolated) confirms the suspected change against tolerance. Step-by-Step Solution: Power down and discharge nearby capacitors for safety.Inspect: look for scorching, cracking, or lifted pads; these indicate overheating.Measure with an ohmmeter: compare measured value to the color-code/marked value and tolerance.Interpretation: significantly higher-than-nominal or infinite resistance indicates damage; sometimes value decreases due to carbonization paths, but increases/open are common. Verification / Alternative check: Cross-check by substituting a known-good resistor of the same value and retesting circuit behavior to confirm that the suspect part was the fault source. Why Other Options Are Wrong: may appear burned: True but not the only indicator. may have an increased resistance value: True; drift/open is frequent after overheating. may be checked with an ohmmeter: True; standard diagnostic method. none of the above: Incorrect because all three are valid indicators. Common Pitfalls: Measuring in-circuit without isolating one lead, causing parallel paths to skew readings. Ignoring tolerance and temperature coefficient when judging small deviations. Overlooking intermittent faults from hairline cracks that change with flex or heat. Final Answer: All of the above

Question 11

Ohm's law defines the fundamental relationship among which three electrical quantities used in circuit analysis and design?

Accepted Answer

Introduction: Ohm's law is the cornerstone of basic circuit theory. It relates voltage (the electrical potential difference), current (the rate of charge flow), and resistance (opposition to current) with a simple proportionality used in virtually every DC and many AC calculations. Given Data / Assumptions: Applies to ohmic (linear) resistive elements over the operating region of interest. Ambient conditions and temperature kept within normal ranges where resistance is approximately constant. Concept / Approach: The relationship is V = I * R. If any two of the quantities are known, the third can be solved directly. This enables sizing of resistors, predicting currents, or determining safe supply voltages. Step-by-Step Solution: Start from V = I * RSolve for current: I = V / RSolve for resistance: R = V / IApply proportionality: doubling V at fixed R doubles I; doubling R at fixed V halves I. Verification / Alternative check: Lab measurements with a resistor and variable DC supply show linear I–V plots passing through the origin, confirming the proportionality embodied in Ohm's law. Why Other Options Are Wrong: voltage, current, and time / resistance, time, and current: Time is not part of the Ohm's law identity. power, current, and resistance: Power relates via P = V * I = I^2 * R = V^2 / R, which derives from Ohm's law but is not the law itself. charge, flux, and inductance: These relate to other electromagnetic concepts, not Ohm's law. Common Pitfalls: Applying Ohm's law to non-linear devices (diodes, lamps) where V–I is not linear. Ignoring temperature effects that change R significantly in some materials. Final Answer: voltage, current, and resistance

Question 12

Ohm's law describes the mathematical relationship between which set of quantities used to calculate basic circuit behavior?

Accepted Answer

Introduction: This question reinforces the definition of Ohm's law from a descriptive angle. Correctly identifying the variables tied by the law is essential for solving everyday circuit problems, from selecting series resistors for LEDs to estimating supply current. Given Data / Assumptions: Ohmic components with linear V–I behavior. Steady-state conditions for DC, or instantaneous relationships for resistive AC. Concept / Approach: Ohm's law: V = I * R links voltage (V), current (I), and resistance (R). Units (ohms, kilohms, megohms) are scales of resistance, not separate physical quantities governed by the law. Step-by-Step Solution: Recognize variables: resistance (R), voltage (V), current (I).Recall the identity: V = I * R.Derive forms: I = V / R and R = V / I.Apply to examples: choose R to set I for a given V in a simple series circuit. Verification / Alternative check: Plotting measured current against applied voltage for a fixed resistor yields a straight line with slope 1/R, confirming the relationship between the three quantities. Why Other Options Are Wrong: ohms, kilohms, and megohms: Merely unit prefixes for resistance. resistor size and resistor value: Physical size does not define the Ohm's law relationship. none of the above / power factor set: Do not describe Ohm's law. Common Pitfalls: Assuming large physical resistors always have large resistance; power rating and resistance are different specifications. Confusing derived power equations with the primary Ohm's law identity. Final Answer: resistance, voltage, and current

Question 13

If the voltage across a fixed resistor is doubled and the current through that resistor also doubles, what can you conclude about the resistor's value?

Accepted Answer

Introduction: This question checks proportional reasoning with Ohm's law. For a linear resistor, current is directly proportional to applied voltage, with resistance as the proportionality constant. If both voltage and current scale by the same factor, resistance remains the same. Given Data / Assumptions: Linear, ohmic resistor behavior over the operating region. Initial and final operating points are within the resistor's power rating (no thermal runaway changing R). Concept / Approach: Ohm's law: R = V / I. If V is multiplied by k and I is multiplied by the same k, then R_new = (k * V) / (k * I) = V / I = R_old. Step-by-Step Solution: Start with R = V / I.Given: V' = 2 * V and I' = 2 * I.Compute: R' = V' / I' = (2 * V) / (2 * I) = V / I = R.Conclusion: Resistance value is unchanged. Verification / Alternative check: Example: A 1 kΩ resistor at 5 V draws 5 mA. Doubling V to 10 V yields 10 mA; R remains 1 kΩ. Measured data of typical metal-film resistors confirm near-constant R over moderate temperature rise. Why Other Options Are Wrong: decreased/increased: Would require I to scale differently than V. impossible to determine: Direct calculation shows R is unchanged. became non-linear: Behavior described is perfectly linear. Common Pitfalls: Forgetting that R is a ratio, not a fixed function of V alone. Confusing power changes (which do double: P = V * I) with resistance change. Final Answer: the resistor value did not change

Question 14

In basic electrical terms, the rate at which work is done or energy is converted per unit time is called what?

Accepted Answer

Introduction: Understanding the distinction between energy and power is vital in circuit design and power budgeting. Energy is the capacity to do work; power is how fast that energy is used or delivered. Given Data / Assumptions: Work and energy measured in joules (J). Power measured in watts (W), where 1 W = 1 J/s. Electrical context: P = V * I in instantaneous terms for resistive loads. Concept / Approach: Power is the time rate of doing work or transferring energy. In circuits, it connects electrical variables to energy conversion (heating, motion, light) through identities such as P = V * I, P = I^2 * R, and P = V^2 / R. Step-by-Step Solution: Define power: P = dW/dt where W is work/energy.Relate to circuits: P = V * I for an element with voltage V and current I.Examples: a 60 W lamp converts 60 J of electrical energy to light/heat each second.Units check: volts * amperes = watts, consistent with joules per second. Verification / Alternative check: Measuring voltage and current with meters and multiplying yields power consumption that matches thermal rise calculations via I^2 * R for resistive loads, confirming the definition operationally. Why Other Options Are Wrong: current: Rate of charge flow (coulombs per second), not energy conversion rate. energy: Total capacity to do work, not the rate. voltage: Potential difference, not a rate of doing work. conductance: Reciprocal of resistance, units of siemens. Common Pitfalls: Confusing watt-hours (energy) with watts (power). Assuming higher voltage alone means higher power without considering current. Final Answer: power

Question 15

How do regulated power supplies differ from batteries when considering output type, stability, and current capability?

Accepted Answer

Introduction: Batteries and regulated power supplies both provide electrical energy to circuits, but their nature and use cases differ. This question checks common misconceptions about output waveform, stability, and current capability. Given Data / Assumptions: Batteries: electrochemical DC sources with finite internal resistance and energy storage. Power supplies: typically convert AC mains to regulated DC (or DC–DC convert), though some supplies deliver AC when designed as inverters. Comparison focuses on general characteristics, not a single special model. Concept / Approach: Most bench and embedded power supplies provide regulated DC outputs, often more stable than raw batteries under varying loads. Current capability ranges widely; many supplies deliver higher currents than small batteries, while some precision supplies are intentionally limited. Therefore, blanket statements in options a–c are incorrect. Step-by-Step Solution: Assess option a: Many power supplies provide DC outputs; claiming they are AC-only is false.Assess option b: Regulation is the hallmark of a quality supply; voltage is typically more stable than a battery under dynamic load.Assess option c: Supplies span from milliampere to hundreds of amperes; not inherently low-current.Therefore, none of the given statements accurately distinguishes power supplies from batteries. Verification / Alternative check: Bench supplies specify load and line regulation (tight stability) and rated output currents; battery datasheets show voltage sag with load and state-of-charge, confirming that supplies can be more stable and not necessarily low-current. Why Other Options Are Wrong: a: Incorrect generalization; most regulated supplies output DC. b: Opposite of typical behavior; regulators aim for stability. c: Not universally true; many supplies provide substantial current. e: Also false; supplies cover wide voltage ranges and are adjustable. Common Pitfalls: Confusing unregulated adapters with regulated supplies. Ignoring internal resistance and state-of-charge effects in batteries. Final Answer: None of the above

Question 16

Ohm’s law application (conceptual): If the voltage across a fixed resistance doubles (R is constant and linear), what happens to the current through that resistance?

Accepted Answer

Introduction: Ohm’s law is a fundamental relationship for linear resistive elements. It directly ties voltage (V), current (I), and resistance (R) through the simple formula V = I * R. Interpreting qualitative changes—like “what if we double the voltage?”—is a core skill in basic circuit analysis and troubleshooting. Given Data / Assumptions: The element is a fixed, linear resistor (R is constant). The voltage across the resistor is doubled. Temperature and nonlinearity effects are ignored. Concept / Approach: From V = I * R, for a constant R, current is proportional to voltage: I = V / R. If V is scaled by a factor k, current scales by the same factor k. Therefore, when the voltage doubles (k = 2), the current must also double, provided R does not change and the device remains in its linear region. Step-by-Step Solution: Start with V = I * R.Solve for current: I = V / R.Let V2 = 2 * V1 with the same R.Then I2 = V2 / R = (2 * V1) / R = 2 * (V1 / R) = 2 * I1. Verification / Alternative check: Pick numbers to validate: let R = 10 Ω, V1 = 5 V → I1 = 0.5 A. Double voltage to V2 = 10 V → I2 = 1.0 A, which is exactly double. This numerical trial confirms the proportionality. Why Other Options Are Wrong: the current is halved: Would require voltage to halve or resistance to double, neither stated. the resistance doubles: R is fixed by the problem statement. the current is unchanged: Only true if voltage is unchanged or R → ∞. Common Pitfalls: Confusing changes in V with changes in R; in this scenario R is constant. Applying Ohm’s law to non-ohmic devices (e.g., lamps, diodes) where I–V is nonlinear. Final Answer: none of the above

Question 17

Power-supply performance — efficiency and internal loss: Is it correct to say that the efficiency rating of a power supply is determined by its internal power loss (i.e., loss mechanisms set how much of the input becomes useful output)?

Accepted Answer

Introduction / Context: Efficiency is a headline metric for any power supply. It directly affects thermal design, size, acoustic noise (fan speed), reliability, and operating cost. This question asks whether the efficiency rating is “determined by internal power loss,” a phrase that connects input power, output power, and the losses inside the converter or regulator. Given Data / Assumptions: Efficiency definition: eta = P_out / P_in. Internal loss: P_loss = P_in − P_out. Steady-state operation; transient storage effects neglected for simplicity. Concept / Approach: From the definitions, eta = P_out / P_in = 1 − (P_loss / P_in). For a given input condition, larger internal losses directly reduce the fraction of power delivered to the load, lowering efficiency. Thus, internal power loss mechanisms—conduction loss, switching loss, magnetic core loss, gate-drive loss, and control/housekeeping power—collectively determine efficiency for specified operating points. Rating tables often show efficiency versus load because losses change with current and duty cycle, but the governing relationship remains the same: minimize losses to maximize efficiency. Step-by-Step Solution: Write P_loss = P_in − P_out.Rearrange to eta = P_out / P_in = 1 − (P_loss / P_in).Observe that increasing P_loss with fixed P_in reduces eta proportionally.Conclude that efficiency is indeed determined by how large internal losses are relative to input power. Verification / Alternative check: Thermal measurements correlate: hotter supplies (more watts lost as heat) show lower efficiency under the same conditions. Efficiency improvements come from reducing loss sources (lower Rds_on, synchronous rectification, better magnetics), confirming the statement. Why Other Options Are Wrong: Incorrect: Contradicts the algebraic identity linking efficiency and loss. Only true for linear supplies: Both linear and switching supplies follow the same energy balance. Only true above 50% load: Efficiency depends on loss at any load; the formula holds universally. Common Pitfalls: Confusing nameplate efficiency at one load with efficiency across all loads; ignoring fixed overhead losses that dominate at light load and conduction/switching losses that dominate at heavy load. Final Answer: Correct.

Question 18

Resistors and heat — desirability of power dissipation: In general-purpose electronics (excluding heaters and special cases), is the heat produced by a resistor a desirable effect, or is it usually an unwanted loss?

Accepted Answer

Introduction / Context: Resistors convert electrical energy into heat through Joule heating. While some applications deliberately use resistors as heaters or current limiters, the overwhelming majority of circuits aim to deliver power to loads like ICs, motors, or LEDs, not to waste it in resistors. This question checks whether heating is generally considered beneficial or undesirable in typical designs. Given Data / Assumptions: Every resistor dissipates P = I^2 * R = V^2 / R = V * I. Ordinary circuits aim for efficiency, reliability, and thermal safety margins. Specialized heater or inrush-limiter roles are not the default case. Concept / Approach: In most designs, heat in resistors is wasted energy that stresses components and raises ambient temperature. Excess heat can shift values (temperature coefficient), accelerate aging, and require larger enclosures or heatsinks. Therefore the statement “Heat produced by a resistor is generally a desirable effect” is false in the general case. Designers size resistor wattage to tolerate unavoidable dissipation while minimizing it by using higher efficiency topologies (e.g., switching regulators instead of large series drop resistors). Step-by-Step Solution: Identify the role: is the resistor intended as a heater? In most circuits, no.Relate heating to efficiency: higher heat implies more loss and lower efficiency.Note design consequences: value drift, reliability concerns, and thermal management overhead.Conclude that heating is generally an unwanted side effect rather than a goal. Verification / Alternative check: Thermal derating curves and resistor power ratings exist precisely because overheating is harmful. Engineers check that P_diss < P_rating and often prefer low-loss solutions to keep temperatures down. Why Other Options Are Wrong: Correct: Not correct; typical circuits avoid unnecessary heat. Only desirable in power wirewound resistors / PTC thermistors: While there are niche uses involving heat, the question asks about general practice—where heating is not desirable. Common Pitfalls: Generalizing from special heater applications; ignoring that even in current limiting, the heat is tolerated, not sought for its own sake. Final Answer: Incorrect.

Question 19

Ohm’s law proportionality — voltage vs. current: Doubling the voltage across a fixed resistor will cut the current by half. Evaluate this statement for a linear (ohmic) resistor.

Accepted Answer

Introduction / Context: Ohm’s law is the foundational relationship between voltage, current, and resistance: V = I * R. Misstatements about proportionality are common in quick reasoning under pressure. This question tests whether doubling the applied voltage across a fixed, linear resistor halves the current, doubles it, or does something else. Given Data / Assumptions: Resistor is linear (ohmic) over the operating range. Resistance R is constant with voltage in the scenario. Ambient and self-heating effects are negligible for the concept check. Concept / Approach: From I = V / R, holding R constant means current is directly proportional to voltage. If V is doubled, I must also double, not be halved. The statement in the stem therefore contradicts Ohm’s law for an ohmic resistor. Non-ohmic devices (lamps, diodes) may not follow V/I linearity, but they are not “resistors” in the ideal Ohm’s law sense posed by the question. Step-by-Step Solution: Start with I1 = V1 / R.Double the voltage: V2 = 2 * V1 while R is unchanged.Compute I2 = V2 / R = (2 * V1) / R = 2 * (V1 / R) = 2 * I1.Conclude that current doubles when voltage doubles across a fixed resistor. Verification / Alternative check: Graphing the I–V curve of a resistor gives a straight line through the origin with slope 1/R. Doubling V moves you to a point with twice the current on the same line—consistent with the direct proportionality. Why Other Options Are Wrong: Correct: Not correct; the correct behavior is doubling, not halving. Only correct for non-ohmic devices: The question states “resistor”; non-ohmic devices are outside scope. Correct only if temperature rises: Temperature coefficients can change R slightly but not invert proportionality to make current half for doubled voltage. Common Pitfalls: Confusing series/parallel changes in R with changes in applied V; attributing non-linear device behavior to ideal resistors. Final Answer: Incorrect.

Question 20

Ohm’s law application — computing current: For a linear resistor, the current through it can be found by dividing the voltage across it by its resistance value. Assess this statement.

Accepted Answer

Introduction / Context: Being fluent with Ohm’s law is essential in electronics. The law ties three quantities—voltage, current, and resistance—into a simple relationship that allows any one to be found if the other two are known. This question checks whether the most common rearrangement, I = V / R, is recognized as valid for a linear resistor. Given Data / Assumptions: Ideal linear (ohmic) resistor. Steady-state DC or RMS sinusoidal AC conditions. No parasitic effects (inductance/capacitance) that would alter the basic relationship. Concept / Approach: Ohm’s law in its basic form is V = I * R. Algebraically solving for current gives I = V / R. This holds for DC and for AC when using RMS values for purely resistive circuits. In the presence of reactance (inductors, capacitors), impedance generalizes resistance, but for a plain resistor, the simple division gives the correct current value. Step-by-Step Solution: Write V = I * R.Rearrange to I = V / R.Identify the measured quantities: V across the resistor and its ohmic value R.Compute I by dividing V by R to obtain amperes. Verification / Alternative check: Lab measurements of a resistor with a known value confirm linear I–V behavior. Plotting current versus voltage yields a straight line with slope 1/R, matching I = V / R at all tested points within tolerance. Why Other Options Are Wrong: Incorrect: Contradicts the defining relationship for resistors. Correct only for AC / only at 25 °C: Ohm’s law applies broadly; temperature changes R slightly but the formula remains valid with the correct R value. Common Pitfalls: Mixing peak and RMS values in AC; neglecting tolerance and temperature coefficients when high precision is needed. Final Answer: Correct.

Ohm's Law Questions