Q: In a Wheatstone bridge at balance, what does the center meter (between the bridge midpoints) read, assuming an ideal meter and source?

Introduction / Context: The Wheatstone bridge is a precision circuit for resistance measurement and sensing (e.g., strain gauges). Balance occurs when the ratio of resistances in one leg equals the ratio in the other leg. At this condition, the detector connected between the two midpoints shows no potential difference. Given Data / Assumptions: Ideal DC source energizing the bridge. Ideal, high-impedance voltmeter or galvanometer connected between the midpoints. Balance condition: R1/R2 = R3/R4 (or equivalently R1 * R4 = R2 * R3). Concept / Approach: At balance, node potentials at the two midpoints are equal, so the meter sees zero differential voltage. With no voltage difference, no current flows through the meter. This is the defining criterion used to adjust an unknown resistor until the bridge is balanced. Step-by-Step Solution: Let V+ be the supply top node and ground the bottom node.Midpoint left: VL = V+ * (R2 / (R1 + R2)).Midpoint right: VR = V+ * (R4 / (R3 + R4)).Balance condition ensures VL = VR, therefore Vmeter = VL − VR = 0 V. Verification / Alternative check: If the bridge is slightly unbalanced, the meter reads a small voltage whose polarity indicates which side is higher—this is how sensitive null measurements are made in practice. Why Other Options Are Wrong: Twice/source/half the source voltage: These imply a nonzero difference, contradicting the equal-potential condition at balance. Common Pitfalls: Confusing equal resistance values with equal ratios; balance requires matched ratios, not necessarily equal resistors. Using a low-impedance meter that perturbs the bridge; an ideal or high-impedance detector is assumed. Final Answer: zero volts

Q: In resistor-network analysis, what fundamental criterion decides whether components are connected in series, in parallel, or in a series–parallel combination?

Introduction / Context: Correctly classifying connections as series or parallel is essential for simplification and design. Students often look at the schematic drawing instead of the actual electrical relationships. The true classification depends on how current and voltage are shared among components and how nodes are connected. Given Data / Assumptions: Passive resistive networks under DC or steady-state conditions. Ideal wires (no resistance) define nodes. No dependent sources inside the elements under discussion. Concept / Approach: Two components are in series if the same current must flow through both (they share a single intermediate node with no branching). Two components are in parallel if both terminals of one are connected to the corresponding two terminals of the other, so their voltages are identical while currents may differ. More complex networks combine these relations to form series–parallel structures. Step-by-Step Solution: Identify nodes: mark all points connected by ideal conductors.Check current path: if only one path exists through two elements sequentially, they are in series.Check voltage sharing: if elements share both end nodes, they are in parallel.If neither condition holds globally, the network is a series–parallel combination or a bridge network. Verification / Alternative check: Use Kirchhoff's laws: series elements share the same current (KCL), parallel elements share the same voltage (KVL around a small loop gives zero difference). Why Other Options Are Wrong: Voltage/power source: The source type does not dictate connection; node topology and current paths do. Resistance value: Magnitude does not determine series/parallel status—connectivity does. Common Pitfalls: Basing judgment on physical drawing proximity rather than node connectivity. Overlooking hidden branches (e.g., measurement instruments or loads) that break series conditions. Final Answer: current flow

Q: For a series–parallel resistor network, what is the correct method to compute each component's power dissipation?

Introduction / Context: Power ratings ensure components operate safely without overheating. In mixed series–parallel circuits, currents and voltages differ across components, so a one-size-fits-all shortcut can be dangerous. The only universally correct approach is to use each element's own voltage and current to compute its power. Given Data / Assumptions: Resistors arranged in a general series–parallel network. Steady-state DC operation. Ohm's law and basic power relations apply. Concept / Approach: For any component: P = V * I = I^2 * R = V^2 / R. Which form you use depends on which quantities are known for that specific element. Because series branches share current and parallel branches share voltage, the element's V and I must be determined locally (not assumed from totals) before computing power. Step-by-Step Solution: 1) Simplify the network as needed to find node voltages and branch currents.2) For each resistor i, determine either Vi or Ii (or both).3) Compute Pi using Pi = Ii^2 * Ri or Pi = Vi^2 / Ri or Pi = Vi * Ii.4) Verify that ΣPi equals the source power (allowing for rounding), ensuring energy conservation. Verification / Alternative check: Kirchhoff's laws guarantee that the sum of individual dissipations equals the input power. Cross-checking with Σ(V_branch * I_branch) provides a robust validation of calculations. Why Other Options Are Wrong: Voltage-division percent squared: Only applies to a simple two-resistor series divider under specific conditions; not general. Total current squared * R: Valid only for elements that actually carry the total current (pure series). It fails in parallel sections. Percent of total power by ratios: Heuristic, not a law; can be grossly inaccurate. Common Pitfalls: Using the same current for all resistors in a mixed network—incorrect for parallel legs. Ignoring tolerance and temperature coefficient that slightly alter actual dissipation. Final Answer: individual component parameters

Q: Series with a parallel branch — R1 is in series with a branch formed by R2 ∥ R3. If R2 becomes open-circuit (while the source voltage stays the same), what happens to the total current drawn from the source?

Introduction: Series–parallel networks are everywhere in real designs. Predicting how a single element failure (such as a branch opening) affects total current is a vital diagnostic skill for troubleshooting and safety analysis. Given Data / Assumptions: Topology: R1 in series with the parallel combination of R2 and R3. Event: R2 opens (infinite resistance), R3 remains unchanged. Source voltage is constant, linear resistive elements only. Concept / Approach: Equivalent resistance of a parallel pair is R_eq = (R2 * R3) / (R2 + R3). When R2 is normal, R_eq < min(R2, R3). If R2 opens, the branch reduces to only R3, so R_eq_new = R3, which is greater than the previous parallel equivalent. Total resistance R_total = R1 + R_eq therefore increases. With a fixed source voltage, the source current I_total = V_source / R_total must decrease when R_total increases. Step-by-Step Solution: Initial: R_eq_initial = (R2 * R3) / (R2 + R3).Failure: R2 → ∞, so R_eq_new = R3.Since R3 > R_eq_initial, then R_total_new = R1 + R3 > R1 + R_eq_initial.Thus I_total_new = V / R_total_new < V / R_total_initial → total current decreases. Verification / Alternative check: Example numbers: let R1 = 100 Ω, R2 = 100 Ω, R3 = 100 Ω. Initially R_eq = 50 Ω and R_total = 150 Ω → I = V / 150. After R2 opens, R_eq = 100 Ω and R_total = 200 Ω → current becomes V / 200, evidently smaller. Why Other Options Are Wrong: increases: Would require a decrease in total resistance, which does not occur when a parallel path is removed. remains the same: Total resistance changed, so current cannot remain identical for a fixed source voltage. cannot tell / oscillates: The DC resistive outcome is deterministic and decreases as shown. Common Pitfalls: Forgetting that removing a parallel branch increases equivalent resistance. Confusing series and parallel effects; series adds, parallel reduces resistance. Final Answer: decreases

Q: All resistors 30 Ω: R1 is in series with a parallel network of R2 and R3 (each 30 Ω). What is the total resistance seen by the source?

Introduction: Combining series and parallel resistors correctly is a foundational skill in circuit analysis. This question checks your ability to compute a simple series–parallel equivalent when all component values are the same, a common exam and lab scenario. Given Data / Assumptions: R1 = 30 Ω in series with the parallel pair R2 ∥ R3. R2 = 30 Ω and R3 = 30 Ω. Ideal conductors and a DC source; no reactive elements. Concept / Approach: For series elements, resistances add directly. For two parallel resistors of equal value R, the equivalent is R/2. Therefore, first reduce the parallel pair to a single equivalent, then add the series resistor to obtain the total resistance presented to the source. Step-by-Step Solution: Compute the parallel equivalent: R_parallel = (R2 * R3) / (R2 + R3) = (30 * 30) / (30 + 30) = 900 / 60 = 15 Ω.Add the series resistor: R_total = R1 + R_parallel = 30 + 15 = 45 Ω.Thus, the network presents 45 Ω to the source.This result is intuitive: adding a 30 Ω in series with a parallel pair that halves to 15 Ω yields 45 Ω. Verification / Alternative check: Using reciprocals: 1 / R_parallel = 1/30 + 1/30 = 2/30 → R_parallel = 15 Ω. Series addition then confirms 45 Ω. Any measurement with a DMM and low test current would read near 45 Ω ignoring lead resistance. Why Other Options Are Wrong: 10 ohms / 20 ohms: Too small; would imply additional parallel paths not present. 90 ohms: Would be the sum if all three were in series, which they are not. 30 ohms: Ignores the added series effect of R1 plus the reduced parallel pair. Common Pitfalls: Accidentally adding all three (30 + 30 + 30) instead of reducing the parallel first. Forgetting that equal parallel resistors halve the value. Final Answer: 45 ohms

Q: Mixed-series/parallel network: Compute the total resistance when R1 = 7 kΩ is in series with a parallel combination of R2 = 20 kΩ, R3 = 36 kΩ, and R4 = 45 kΩ. Show the correct equivalent of the parallel branch added to R1.

Introduction / Context: This problem checks your ability to simplify a resistor network that combines both parallel and series connections. Such reductions are routine in circuit analysis before applying Ohm's law, Thevenin equivalents, or power calculations. The key is to first collapse the parallel branch to a single equivalent resistance and then add the series resistor. Given Data / Assumptions: R1 = 7 kΩ in series with a parallel network. Parallel network: R2 = 20 kΩ, R3 = 36 kΩ, R4 = 45 kΩ. All components are ideal resistors; temperature and tolerance effects ignored. Concept / Approach: For parallel resistors, use the conductance-sum rule. The parallel equivalent is given by 1/Rp = 1/R2 + 1/R3 + 1/R4. After finding Rp, add R1 in series: R_total = R1 + Rp. Keeping units consistent (kΩ) avoids mistakes. Step-by-Step Solution: Compute parallel conductance: 1/Rp = 1/20 + 1/36 + 1/45 (all in kΩ^-1).Evaluate numerically: 1/20 = 0.05; 1/36 ≈ 0.02778; 1/45 ≈ 0.02222; sum = 0.10.Find Rp: Rp = 1 / 0.10 = 10 kΩ.Add series R1: R_total = 7 kΩ + 10 kΩ = 17 kΩ. Verification / Alternative check: If you replace the three parallel resistors by 10 kΩ and measure the total with an ohmmeter across the two ends of the whole string, you would read approximately 17 kΩ, confirming the arithmetic. Why Other Options Are Wrong: 4 kΩ: Much too small; parallel of 20, 36, 45 kΩ cannot be below the smallest 20 kΩ by that much, and series with 7 kΩ would increase the total. 41 kΩ / 108 kΩ: These ignore the strong reduction due to the parallel branch and/or wrongly add all values. Common Pitfalls: Accidentally adding parallel resistances directly (incorrect) or forgetting to convert units consistently. Always compute the parallel equivalent first, then add series resistances. Final Answer: 17 kΩ

Question 1

Mixed series–parallel network: With a 6 V source, R1 = 2 kΩ is in series with a parallel network of R2 = 1 kΩ, R3 = 2 kΩ, and R4 = 1 kΩ. What is the voltage across resistor R2 (i.e., across the entire parallel branch)?

Accepted Answer

Introduction / Context: Analyzing series–parallel circuits often reduces to two steps: first find the equivalent resistance of parallel sub-networks, then apply series rules such as the voltage divider. This problem illustrates that workflow and emphasizes that the same voltage appears across all elements of a parallel branch. Given Data / Assumptions: Source voltage V_s = 6 V. Series resistor R1 = 2 kΩ. Parallel branch: R2 = 1 kΩ, R3 = 2 kΩ, R4 = 1 kΩ. All components are ideal; DC steady-state analysis. Concept / Approach: First, compute the equivalent resistance of the parallel network: 1/R_p = 1/R2 + 1/R3 + 1/R4. Then form a simple series pair of R1 and R_p. The voltage across the parallel branch is found by the divider V_parallel = V_s * (R_p / (R1 + R_p)). The voltage across R2 equals the branch voltage because nodes are common in parallel. Step-by-Step Solution: Compute 1/R_p = 1/1000 + 1/2000 + 1/1000 = 0.001 + 0.0005 + 0.001 = 0.0025.So R_p = 1 / 0.0025 = 400 Ω.Total series resistance: R_total = R1 + R_p = 2000 + 400 = 2400 Ω.Voltage divider: V_parallel = 6 * (400 / 2400) = 6 * (1/6) = 1 V.Since R2 is in that parallel branch, V_R2 = 1 V. Verification / Alternative check: Calculate branch currents: I_total = 6 / 2400 = 2.5 mA. Current through R1 causes a drop of V_R1 = I_total * 2000 = 5 V. Remaining voltage across the parallel network is 6 − 5 = 1 V, confirming the divider result. Why Other Options Are Wrong: 3 V or 5 V: would require different series/parallel proportions; they contradict divider math.6 V: would be correct only if R1 = 0 (no series drop), which is not the case. Common Pitfalls: Forgetting that all components in parallel share the same voltage, or miscomputing R_p by adding resistances instead of conductances (reciprocals). Keep careful track of units (kΩ vs Ω). Final Answer: 1 V

Question 2

Network equivalence theorems: Which theorem allows replacing a linear, bilateral two-terminal network with an equivalent circuit consisting of a single voltage source in series with a single resistance?

Accepted Answer

Introduction / Context: Equivalence theorems simplify complex networks into basic source–resistance models that are easier to analyze, especially when studying the effect of varying loads. Recognizing whether to use Thevenin or Norton form is a staple skill in circuit theory and lab measurement practice. Given Data / Assumptions: Network is linear and bilateral (resistors, independent/dependent sources, and linear elements). Two-terminal view toward the load. Goal: replace with a simple, functionally equivalent source–resistance pair. Concept / Approach: Thevenin’s theorem states any linear two-terminal network can be replaced by an equivalent voltage source V_th in series with a resistance R_th as seen from the load terminals. Norton’s theorem is the dual form using a current source I_no in parallel with R_no, where V_th = I_no * R_th and R_th = R_no. Superposition is a technique for analyzing circuits with multiple sources; it is not an equivalence replacement. “Multinetwork” is not a standard theorem. Step-by-Step Solution: Find V_th: compute open-circuit voltage at the terminals.Find R_th: zero independent sources (voltage sources → short, current sources → open) and compute equivalent resistance seen from the terminals.Form the Thevenin equivalent: a single ideal voltage source V_th in series with R_th.Connect the load to analyze currents/voltages easily. Verification / Alternative check: Convert between Thevenin and Norton: I_no = V_th / R_th and R_no = R_th. Solving a sample network both ways yields identical load behavior, confirming equivalence. Why Other Options Are Wrong: Norton: equivalent current source with parallel resistance, not a series resistance with a voltage source.Superposition: analysis method, not a replacement theorem.Multinetwork: not a recognized theorem in basic circuit theory. Common Pitfalls: Confusing how to compute R_th in the presence of dependent sources (a test source is then required). Always apply the correct procedures for networks with dependent elements. Final Answer: Thevenin

Question 3

First objective in series–parallel analysis: When approaching a complex series–parallel circuit, what should be the first goal to accomplish in order to simplify subsequent steps?

Accepted Answer

Introduction / Context: Effective analysis of mixed series–parallel networks follows a logical sequence. Establishing the global behavior first makes local calculations straightforward and reduces the chance of arithmetic or conceptual errors. This question asks for the appropriate first objective. Given Data / Assumptions: Circuit contains a combination of series and parallel elements. Source values are known. Goal is to find currents and voltages throughout the network. Concept / Approach: The most efficient starting point is to reduce the network to an equivalent total resistance and use it with the known source to determine total current. With total current and the high-level equivalent known, you can progressively “expand” the circuit back out, computing intermediate node voltages and branch currents via divider rules and parallel current splits. Jumping directly to every voltage drop without a global reference invites mistakes. Step-by-Step Solution: Combine obvious series or parallel groups into a single equivalent resistance step by step.Compute the overall equivalent resistance R_eq as seen by the source.Use Ohm’s law to find the total current: I_total = V_source / R_eq.Back-substitute: from the source toward the loads, split currents at parallel nodes and apply voltage division across series parts to find individual drops. Verification / Alternative check: Perform a quick power balance: P_source = V_source * I_total should equal the sum of I^2 * R losses in all elements after detailed calculations. Matching totals confirms consistency. Why Other Options Are Wrong: Equate all parallel or series components: you cannot equate dissimilar values; you reduce them to equivalents, but that is part of building R_eq, not an end in itself.Solve for all voltage drops: without I_total and key node voltages, this is premature and error-prone. Common Pitfalls: Ignoring unit conversions (Ω, kΩ) and rounding too early. Another pitfall is forgetting that total current is unique to the source loop but branches split according to conductances in parallel sections. Final Answer: solve for the total current and resistance

Question 4

In a DC voltage divider that is not supplying any external load (i.e., the divider is unloaded), what is the name of the internal current that continuously flows through the divider resistors?

Accepted Answer

Introduction / Context: A voltage divider is a simple network of resistors used to generate a stable, lower voltage from a higher supply. Even when no external circuit is connected to the divider's output node (that is, it is unloaded), current still flows through the series resistors. Knowing the correct terminology for this internal current is essential for power budgeting and understanding loading effects. Given Data / Assumptions: Two or more resistors are connected in series across a DC supply. No external load is connected to the divider output node (unloaded condition). Steady-state DC operation; resistors are ideal. Concept / Approach: With an unloaded divider, the current that flows from the supply through the series string returns to the supply without doing useful work for a load. This standing current is historically called the bleeder current. It sets the quiescent power dissipation of the divider and provides a defined output impedance. When a load is added, part of the current diverts into the load and the output voltage can sag depending on the divider's design. Step-by-Step Solution: Identify the current path: source → R1 → R2 (→ …) → source return.Compute magnitude if needed: I_bleeder = V_in / R_total (no load present).Recognize terminology: this standing current is widely termed “bleeder current.”Therefore, the correct name is bleeder current. Verification / Alternative check: Power supplies often include a permanent resistor from output to return called a bleeder to discharge capacitors and set a minimum load. Its current is likewise called bleeder current, matching the divider case. Why Other Options Are Wrong: Resistor current/divider feed current: informal or ambiguous terms; the standard term is bleeder current. Load current: zero in an unloaded divider. Voltage current: not a standard electrical term. Common Pitfalls: Underestimating bleeder power loss. The power wasted is P = I_bleeder^2 * R_total, which must be considered for efficiency and resistor wattage ratings. Final Answer: bleeder current

Question 5

Consider a network where resistor R1 is in series with a parallel combination of R2, R3, and R4 across a fixed DC source. If only R2 increases in resistance (R1, R3, R4, and the source remain unchanged), how does the voltage across R3 change?

Accepted Answer

Introduction / Context: Series–parallel circuits appear in practical voltage dividers and sensor networks. Understanding how a change in one branch resistor affects voltages elsewhere builds strong intuition for troubleshooting and design sensitivity analysis. Given Data / Assumptions: Topology: R1 in series with a parallel network consisting of R2, R3, and R4. Only R2 changes (increases). R1, R3, R4, and the supply voltage remain constant. We seek the direction of change of the voltage across R3. Concept / Approach: The voltage across R3 is the same as the voltage across the entire parallel network (since branches in parallel share the same voltage). Let Rp be the equivalent resistance of the parallel block. The series divider relation for the parallel block is Vp = Vs * (Rp / (R1 + Rp)). If R2 increases, Rp increases (the parallel equivalent increases when one branch resistance increases), and the divider formula shows that Vp increases monotonically with Rp. Step-by-Step Solution: Define Rp = (1 / (1/R2 + 1/R3 + 1/R4))When R2 increases, 1/R2 decreases → the sum (1/R2 + 1/R3 + 1/R4) decreases → Rp increases.Voltage across R3 equals Vp = Vs * Rp / (R1 + Rp).Differentiate or reason monotonicity: dVp/dRp = Vs * R1 / (R1 + Rp)^2 > 0.Therefore, Vp (and hence VR3) increases. Verification / Alternative check: Pick numbers: R1 = 1 kΩ, R2 = 1 kΩ → Rp_initial; then double R2 to 2 kΩ → Rp grows; computing the divider shows the parallel-node voltage rises, confirming the conclusion. Why Other Options Are Wrong: Decrease/remain the same: contradict the divider dependence on Rp; as Rp rises, the parallel node takes a larger share of the source voltage. Cannot tell/oscillate: the effect is deterministic for fixed DC resistive networks. Common Pitfalls: Confusing voltage sharing in the parallel block (common voltage) with current sharing (different in each branch). Also, remember that raising one branch resistance increases the overall parallel equivalent (though with diminishing sensitivity). Final Answer: increase

Question 6

A series–parallel circuit has two resistors R1 and R2 in series forming one branch, and that series branch is connected in parallel with resistor R3 across a DC source. If R1 becomes an open circuit (fails open), what happens to the voltage across R…

Accepted Answer

Introduction / Context: Diagnosing faults in mixed series–parallel networks requires predicting how voltages redistribute when a component fails. An open-circuit failure interrupts current in its path, dramatically altering voltages on that branch. Given Data / Assumptions: R1 and R2 are in series, and this series branch is in parallel with R3. R1 fails open (infinite resistance). Ideal DC source; no unintended leakage paths. Concept / Approach: With R1 open, the R1–R2 branch is broken. No current can flow through R2 because the series path is incomplete. For an ideal resistor, voltage across it is V = I * R. With I = 0 A through R2, its voltage must be 0 V. Therefore, relative to the normal operating condition (nonzero current), the voltage across R2 decreases (it drops to zero). Step-by-Step Solution: Model the fault: R1 → ∞ (open circuit).Branch current: I_branch = Vs / (R1 + R2) → 0 A because R1 + R2 → ∞.Voltage across R2: VR2 = I_branch * R2 = 0 A * R2 = 0 V.Conclusion: The voltage across R2 decreases to zero compared to the healthy state. Verification / Alternative check: Measure with a voltmeter in practice: after R1 opens, VR2 collapses to 0 V, while the parallel resistor R3 may still carry current and drop nearly the full source voltage across itself. Why Other Options Are Wrong: Increase/remain the same: impossible with zero branch current through an ideal resistor. Cannot tell: the behavior follows directly from V = I * R and an open path (I = 0). Reverse polarity: no current, hence no defined polarity drop across R2. Common Pitfalls: Assuming some voltage must appear across every resistor. In series branches that are opened, ideal resistors see zero current and therefore zero drop. Final Answer: decrease

Question 7

In a series–parallel circuit, components (or groups of components) that share the same current—meaning the very same charges pass sequentially through them—are said to be in what relationship?

Accepted Answer

Introduction / Context: Recognizing whether elements are in series or in parallel is fundamental to predicting how voltages and currents distribute in a circuit. The defining signature of a series connection is a single, unbroken path for current shared by the elements in that series chain. Given Data / Assumptions: Mixed series–parallel networks may include branches and junctions. Two elements are said to have a common current if the same current flows through them consecutively. Ideal conductors and steady-state conditions are assumed. Concept / Approach: Elements in series share the same current because the charge that exits one must immediately enter the next—there is no node where the current can split or combine. In contrast, elements in parallel share the same voltage because both are connected across the same pair of nodes, but their currents can differ based on their resistances. Step-by-Step Solution: Identify whether there is a junction between the two elements where current can divide. If not, they are in series.Apply KCL: with no branching node, I_in to the first element equals I_out from the second element, so the current is common to both.Apply KVL for voltage distribution if needed; series elements divide the applied voltage based on their impedances.Conclude that components with common currents are in series with each other. Verification / Alternative check: Measure with an ammeter placed in series before and after two suspected elements. Equal readings confirm a series relationship. Parallel elements would show equal node voltages but not necessarily equal currents. Why Other Options Are Wrong: Parallel: defines common voltage, not common current. Either/none/isolation: these are vague or incorrect; the precise relationship for common current is series. Common Pitfalls: Misidentifying nodes where conductors split or rejoin, which breaks the series condition. Always trace the exact path of current between nodes. Final Answer: series with each other

Question 8

A 21 V source is applied to a network where R1 = 5 Ω is in series with a parallel branch consisting of R2 = 35 Ω and R3 = 14 Ω. What is the current through resistor R2 under these conditions?

Accepted Answer

Introduction / Context: This numerical problem checks series–parallel reduction and the use of Ohm's law to find a branch current. The network is a classic case: one resistor in series with a parallel pair. We first find the equivalent resistance seen by the source, then the voltage across the parallel branch, and finally the individual branch current through R2. Given Data / Assumptions: Source voltage Vs = 21 V (DC). R1 = 5 Ω in series with the parallel combination of R2 and R3. R2 = 35 Ω, R3 = 14 Ω. Resistors are ideal; wiring resistance is negligible. Concept / Approach: Use series–parallel reduction and Ohm's law. For the parallel branch, compute R23 using 1/R23 = 1/R2 + 1/R3. The total series resistance is R_total = R1 + R23. The series current is I_total = Vs / R_total. The voltage across the parallel branch is V_parallel = Vs − (I_total * R1) (equivalently I_total * R23). Current through R2 is I_R2 = V_parallel / R2. Step-by-Step Solution: 1) Compute R23: 1/R23 = 1/35 + 1/14 = 0.028571... + 0.071428... = 0.100000Thus R23 = 1 / 0.1 = 10 Ω2) Total series resistance: R_total = R1 + R23 = 5 + 10 = 15 Ω3) Series current: I_total = Vs / R_total = 21 / 15 = 1.4 A4) Voltage across parallel branch: V_parallel = I_total * R23 = 1.4 * 10 = 14 V5) Branch current through R2: I_R2 = V_parallel / R2 = 14 / 35 = 0.4 A = 400 mA Verification / Alternative check: Compute I through R3: I_R3 = 14/14 = 1 A. Check that I_R2 + I_R3 = 0.4 + 1.0 = 1.4 A, which equals the series current found earlier—consistent by Kirchhoff's Current Law. Why Other Options Are Wrong: 200 mA, 600 mA, 800 mA: These do not satisfy both the branch voltage (14 V) and Ohm's law for R2 = 35 Ω. Common Pitfalls: Mistaking the parallel equivalent (it is 10 Ω, not 49 Ω). Using source voltage directly across R2 without accounting for the series R1 drop. Final Answer: 400 mA

Question 9

In a practical voltage divider, when a load is connected across one of the divider's output nodes, how does the total equivalent resistance seen by the source change?

Accepted Answer

Introduction / Context: Voltage dividers are widely used to derive lower voltages or reference levels. However, connecting a load across a tap changes the divider's behavior. Understanding how the load alters the total equivalent resistance seen by the source is key to predicting the new currents and voltages (loading effect). Given Data / Assumptions: A two-resistor divider (or multi-resistor ladder) is driven by a source. A load resistor RL is connected from the output node to ground (or the lower node). All components are linear, and connections are ideal. Concept / Approach: When the load is attached, it appears in parallel with the lower divider resistor (or with a segment of the ladder). The parallel combination is always less than or equal to the smallest of the two resistances. Therefore, the total equivalent resistance from the source terminal, which includes that parallel combination, must decrease relative to the unloaded divider. Step-by-Step Solution: Let the divider be Rtop in series with Rbottom.Without load: Req_unloaded = Rtop + Rbottom.With load RL across Rbottom: Rbottom_loaded = (Rbottom * RL) / (Rbottom + RL).New total: Req_loaded = Rtop + Rbottom_loaded.Since Rbottom_loaded <= Rbottom, we have Req_loaded <= Req_unloaded. Verification / Alternative check: Example: Rtop = 10 kΩ, Rbottom = 10 kΩ. Unloaded Req = 20 kΩ. With RL = 10 kΩ, Rbottom_loaded = 10k||10k = 5 kΩ, so Req_loaded = 15 kΩ, clearly decreased. Why Other Options Are Wrong: Double / increase / remain the same: A parallel addition cannot increase the equivalent resistance or leave it unchanged unless RL is infinite (no load). In normal loading, it decreases. Common Pitfalls: Ignoring loading and assuming the divider ratio is unchanged; output voltage will droop under load. Forgetting to compute the parallel combination Rbottom||RL. Final Answer: decrease

Question 10

In a Wheatstone bridge at balance, what does the center meter (between the bridge midpoints) read, assuming an ideal meter and source?

Accepted Answer

Introduction / Context: The Wheatstone bridge is a precision circuit for resistance measurement and sensing (e.g., strain gauges). Balance occurs when the ratio of resistances in one leg equals the ratio in the other leg. At this condition, the detector connected between the two midpoints shows no potential difference. Given Data / Assumptions: Ideal DC source energizing the bridge. Ideal, high-impedance voltmeter or galvanometer connected between the midpoints. Balance condition: R1/R2 = R3/R4 (or equivalently R1 * R4 = R2 * R3). Concept / Approach: At balance, node potentials at the two midpoints are equal, so the meter sees zero differential voltage. With no voltage difference, no current flows through the meter. This is the defining criterion used to adjust an unknown resistor until the bridge is balanced. Step-by-Step Solution: Let V+ be the supply top node and ground the bottom node.Midpoint left: VL = V+ * (R2 / (R1 + R2)).Midpoint right: VR = V+ * (R4 / (R3 + R4)).Balance condition ensures VL = VR, therefore Vmeter = VL − VR = 0 V. Verification / Alternative check: If the bridge is slightly unbalanced, the meter reads a small voltage whose polarity indicates which side is higher—this is how sensitive null measurements are made in practice. Why Other Options Are Wrong: Twice/source/half the source voltage: These imply a nonzero difference, contradicting the equal-potential condition at balance. Common Pitfalls: Confusing equal resistance values with equal ratios; balance requires matched ratios, not necessarily equal resistors. Using a low-impedance meter that perturbs the bridge; an ideal or high-impedance detector is assumed. Final Answer: zero volts

Question 11

In resistor-network analysis, what fundamental criterion decides whether components are connected in series, in parallel, or in a series–parallel combination?

Accepted Answer

Introduction / Context: Correctly classifying connections as series or parallel is essential for simplification and design. Students often look at the schematic drawing instead of the actual electrical relationships. The true classification depends on how current and voltage are shared among components and how nodes are connected. Given Data / Assumptions: Passive resistive networks under DC or steady-state conditions. Ideal wires (no resistance) define nodes. No dependent sources inside the elements under discussion. Concept / Approach: Two components are in series if the same current must flow through both (they share a single intermediate node with no branching). Two components are in parallel if both terminals of one are connected to the corresponding two terminals of the other, so their voltages are identical while currents may differ. More complex networks combine these relations to form series–parallel structures. Step-by-Step Solution: Identify nodes: mark all points connected by ideal conductors.Check current path: if only one path exists through two elements sequentially, they are in series.Check voltage sharing: if elements share both end nodes, they are in parallel.If neither condition holds globally, the network is a series–parallel combination or a bridge network. Verification / Alternative check: Use Kirchhoff's laws: series elements share the same current (KCL), parallel elements share the same voltage (KVL around a small loop gives zero difference). Why Other Options Are Wrong: Voltage/power source: The source type does not dictate connection; node topology and current paths do. Resistance value: Magnitude does not determine series/parallel status—connectivity does. Common Pitfalls: Basing judgment on physical drawing proximity rather than node connectivity. Overlooking hidden branches (e.g., measurement instruments or loads) that break series conditions. Final Answer: current flow

Question 12

In real products and test setups, how are electronic components most commonly interconnected within a circuit overall?

Accepted Answer

Introduction / Context: Most practical circuits are not purely series or purely parallel. Power distribution, bias networks, filters, dividers, and sensing elements are arranged to meet multiple objectives. Recognizing that real designs blend series and parallel connections helps in understanding schematics and predicting performance. Given Data / Assumptions: General electronic assemblies (analog and digital). Multiple subcircuits with differing functions (supply, signal, protection). Standard interconnects using nodes and nets on PCBs. Concept / Approach: Series connections are used where the same current must flow through elements (e.g., current-sense resistors, series protection). Parallel connections provide common voltages and current sharing (e.g., decoupling capacitors, resistor ladders, pull-ups). Combining them yields voltage dividers, RC filters, bias trees, and bridge networks, forming the fabric of real designs. Step-by-Step Example: Power input: A fuse and NTC in series with the line; bulk caps in parallel across the rails.Bias network: Series resistors feeding a transistor base with parallel bypass capacitors.Signal chain: Series coupling capacitors with shunt (parallel) bias resistors.These together form a series–parallel overall topology. Verification / Alternative check: Inspect any typical schematic (e.g., audio preamp, MCU board). You will find both series elements (current-limiting, sensing) and parallel elements (decoupling, pull-ups), proving the ubiquity of mixed topologies. Why Other Options Are Wrong: Positive-to-positive: Polarity matching alone does not describe interconnection topology. Pure parallel or pure series: Rare outside of didactic examples; practical circuits mix both. Common Pitfalls: Assuming a single simplification method will reduce an entire schematic; parts may not be reducible due to bridges or active devices. Ignoring return paths and grounds, which create parallel branches even when the main path looks series. Final Answer: as a combination of series and parallel

Question 13

For a series–parallel resistor network, what is the correct method to compute each component's power dissipation?

Accepted Answer

Introduction / Context: Power ratings ensure components operate safely without overheating. In mixed series–parallel circuits, currents and voltages differ across components, so a one-size-fits-all shortcut can be dangerous. The only universally correct approach is to use each element's own voltage and current to compute its power. Given Data / Assumptions: Resistors arranged in a general series–parallel network. Steady-state DC operation. Ohm's law and basic power relations apply. Concept / Approach: For any component: P = V * I = I^2 * R = V^2 / R. Which form you use depends on which quantities are known for that specific element. Because series branches share current and parallel branches share voltage, the element's V and I must be determined locally (not assumed from totals) before computing power. Step-by-Step Solution: 1) Simplify the network as needed to find node voltages and branch currents.2) For each resistor i, determine either Vi or Ii (or both).3) Compute Pi using Pi = Ii^2 * Ri or Pi = Vi^2 / Ri or Pi = Vi * Ii.4) Verify that ΣPi equals the source power (allowing for rounding), ensuring energy conservation. Verification / Alternative check: Kirchhoff's laws guarantee that the sum of individual dissipations equals the input power. Cross-checking with Σ(V_branch * I_branch) provides a robust validation of calculations. Why Other Options Are Wrong: Voltage-division percent squared: Only applies to a simple two-resistor series divider under specific conditions; not general. Total current squared * R: Valid only for elements that actually carry the total current (pure series). It fails in parallel sections. Percent of total power by ratios: Heuristic, not a law; can be grossly inaccurate. Common Pitfalls: Using the same current for all resistors in a mixed network—incorrect for parallel legs. Ignoring tolerance and temperature coefficient that slightly alter actual dissipation. Final Answer: individual component parameters

Question 14

Wheatstone bridge measurement principle: In classical electrical measurements, a Wheatstone bridge is primarily used to determine which unknown quantity by balancing two resistor ratios and detecting a galvanometer null?

Accepted Answer

Introduction: The Wheatstone bridge is one of the most important null-measurement circuits in electrical engineering. It enables highly accurate comparison of resistances by balancing two arms of a bridge and observing a zero-current (null) condition through a sensitive detector. Understanding what physical quantity the bridge is designed to find clarifies why it is ubiquitous in sensor interfacing and precision metrology. Given Data / Assumptions: A four-resistor network arranged as a bridge: two known standard resistors, one variable/ratio resistor, and one unknown element. A sensitive null detector (galvanometer or differential amplifier) between the midpoints of the two arms. A stable DC source feeding the bridge. Concept / Approach: At balance, the ratio of the two resistors in one arm equals the ratio in the other arm. The null condition means no current flows through the detector, allowing a ratio equation to be written that directly solves for the unknown resistance. Because this is a ratio method at null, it minimizes the influence of source voltage drift and detector calibration errors, yielding high accuracy for resistance determination. Step-by-Step Solution: Label arms so that R1 and R2 form one leg, and R3 and RUNK form the other.At balance: R1 / R2 = R3 / RUNK.Rearrange to solve for the unknown: RUNK = (R2 * R3) / R1.Since balance is detected by zero current through the detector, measurement accuracy relies on resistive ratios, not on knowing the exact source voltage. Verification / Alternative check: By substituting any three known resistor values into the balance equation and computing RUNK, then re-checking the ratio equality, you verify the bridge principle. Practical bridges use precision ratio arms and variable resistors to dial in balance exactly. Why Other Options Are Wrong: current: The detector monitors near-zero current at balance; current is not what is determined as an unknown. power: Power depends on both voltage and current and is not directly measured by the bridge balance condition. voltage: The source voltage cancels in the ratio; voltage magnitude is not the bridge’s unknown. frequency: A DC Wheatstone bridge is not a frequency-measuring device. Common Pitfalls: Assuming you need the exact source voltage; you do not at balance because of the ratio method. Ignoring lead and contact resistances, which can disturb balance in low-ohm measurements; use Kelvin (4-wire) techniques when needed. Final Answer: resistance

Question 15

Series with a parallel branch — R1 is in series with a branch formed by R2 ∥ R3. If R2 becomes open-circuit (while the source voltage stays the same), what happens to the total current drawn from the source?

Accepted Answer

Introduction: Series–parallel networks are everywhere in real designs. Predicting how a single element failure (such as a branch opening) affects total current is a vital diagnostic skill for troubleshooting and safety analysis. Given Data / Assumptions: Topology: R1 in series with the parallel combination of R2 and R3. Event: R2 opens (infinite resistance), R3 remains unchanged. Source voltage is constant, linear resistive elements only. Concept / Approach: Equivalent resistance of a parallel pair is R_eq = (R2 * R3) / (R2 + R3). When R2 is normal, R_eq < min(R2, R3). If R2 opens, the branch reduces to only R3, so R_eq_new = R3, which is greater than the previous parallel equivalent. Total resistance R_total = R1 + R_eq therefore increases. With a fixed source voltage, the source current I_total = V_source / R_total must decrease when R_total increases. Step-by-Step Solution: Initial: R_eq_initial = (R2 * R3) / (R2 + R3).Failure: R2 → ∞, so R_eq_new = R3.Since R3 > R_eq_initial, then R_total_new = R1 + R3 > R1 + R_eq_initial.Thus I_total_new = V / R_total_new < V / R_total_initial → total current decreases. Verification / Alternative check: Example numbers: let R1 = 100 Ω, R2 = 100 Ω, R3 = 100 Ω. Initially R_eq = 50 Ω and R_total = 150 Ω → I = V / 150. After R2 opens, R_eq = 100 Ω and R_total = 200 Ω → current becomes V / 200, evidently smaller. Why Other Options Are Wrong: increases: Would require a decrease in total resistance, which does not occur when a parallel path is removed. remains the same: Total resistance changed, so current cannot remain identical for a fixed source voltage. cannot tell / oscillates: The DC resistive outcome is deterministic and decreases as shown. Common Pitfalls: Forgetting that removing a parallel branch increases equivalent resistance. Confusing series and parallel effects; series adds, parallel reduces resistance. Final Answer: decreases

Question 16

Analyzing complex series–parallel circuits: As a first objective, what should you determine to establish a solid baseline for all subsequent voltage and current calculations?

Accepted Answer

Introduction: When confronted with a complex series–parallel network, a disciplined workflow avoids confusion and errors. The most productive starting point is to reduce the circuit to an equivalent seen by the source and determine the total current and total resistance. This foundation makes subsequent back-calculations straightforward and consistent with Kirchhoff’s laws. Given Data / Assumptions: Linear DC resistive network composed of series and parallel groupings. Single known source (voltage or current) is driving the network. No dependent sources or reactive components in the initial analysis. Concept / Approach: The standard approach is to collapse the network: combine obvious series elements by addition and parallel elements by product-over-sum (or reciprocal addition). This stepwise reduction yields an equivalent resistance. With a known source voltage, compute the total current; with a known source current, compute the total voltage. These totals then govern every branch calculation via current or voltage division rules. Step-by-Step Solution: Identify series groups: R_series = R_a + R_b + …Identify parallel groups: R_parallel = (R_x * R_y) / (R_x + R_y) or 1 / (1/R1 + 1/R2 + …)Iteratively reduce until a single R_eq remains.Compute I_total = V_source / R_eq (or V_total = I_source * R_eq).Back-annotate: use voltage division V_k = I_total * R_k for series and current division I_branch = V_node / R_branch for parallel sections. Verification / Alternative check: Cross-check with Kirchhoff’s Current Law at nodes and Kirchhoff’s Voltage Law around loops. Simulated or measured totals should match your calculated I_total and R_eq; discrepancies indicate a reduction or arithmetic error. Why Other Options Are Wrong: Equate all parallel/series components: Equalizing values is not a method; combining them numerically is. Solve for all voltage drops first: Without I_total or R_eq, drops are unknown; sequence is backwards. Measure ripple first: Irrelevant in ideal DC resistive analysis. Common Pitfalls: Jumping into local sub-circuits without first finding the global equivalent can lead to inconsistent node voltages. Ignoring unit consistency (Ω, kΩ) and rounding too early. Final Answer: solve for the total current and resistance

Question 17

All resistors 30 Ω: R1 is in series with a parallel network of R2 and R3 (each 30 Ω). What is the total resistance seen by the source?

Accepted Answer

Introduction: Combining series and parallel resistors correctly is a foundational skill in circuit analysis. This question checks your ability to compute a simple series–parallel equivalent when all component values are the same, a common exam and lab scenario. Given Data / Assumptions: R1 = 30 Ω in series with the parallel pair R2 ∥ R3. R2 = 30 Ω and R3 = 30 Ω. Ideal conductors and a DC source; no reactive elements. Concept / Approach: For series elements, resistances add directly. For two parallel resistors of equal value R, the equivalent is R/2. Therefore, first reduce the parallel pair to a single equivalent, then add the series resistor to obtain the total resistance presented to the source. Step-by-Step Solution: Compute the parallel equivalent: R_parallel = (R2 * R3) / (R2 + R3) = (30 * 30) / (30 + 30) = 900 / 60 = 15 Ω.Add the series resistor: R_total = R1 + R_parallel = 30 + 15 = 45 Ω.Thus, the network presents 45 Ω to the source.This result is intuitive: adding a 30 Ω in series with a parallel pair that halves to 15 Ω yields 45 Ω. Verification / Alternative check: Using reciprocals: 1 / R_parallel = 1/30 + 1/30 = 2/30 → R_parallel = 15 Ω. Series addition then confirms 45 Ω. Any measurement with a DMM and low test current would read near 45 Ω ignoring lead resistance. Why Other Options Are Wrong: 10 ohms / 20 ohms: Too small; would imply additional parallel paths not present. 90 ohms: Would be the sum if all three were in series, which they are not. 30 ohms: Ignores the added series effect of R1 plus the reduced parallel pair. Common Pitfalls: Accidentally adding all three (30 + 30 + 30) instead of reducing the parallel first. Forgetting that equal parallel resistors halve the value. Final Answer: 45 ohms

Question 18

Mixed-series/parallel network: Compute the total resistance when R1 = 7 kΩ is in series with a parallel combination of R2 = 20 kΩ, R3 = 36 kΩ, and R4 = 45 kΩ. Show the correct equivalent of the parallel branch added to R1.

Accepted Answer

Introduction / Context: This problem checks your ability to simplify a resistor network that combines both parallel and series connections. Such reductions are routine in circuit analysis before applying Ohm's law, Thevenin equivalents, or power calculations. The key is to first collapse the parallel branch to a single equivalent resistance and then add the series resistor. Given Data / Assumptions: R1 = 7 kΩ in series with a parallel network. Parallel network: R2 = 20 kΩ, R3 = 36 kΩ, R4 = 45 kΩ. All components are ideal resistors; temperature and tolerance effects ignored. Concept / Approach: For parallel resistors, use the conductance-sum rule. The parallel equivalent is given by 1/Rp = 1/R2 + 1/R3 + 1/R4. After finding Rp, add R1 in series: R_total = R1 + Rp. Keeping units consistent (kΩ) avoids mistakes. Step-by-Step Solution: Compute parallel conductance: 1/Rp = 1/20 + 1/36 + 1/45 (all in kΩ^-1).Evaluate numerically: 1/20 = 0.05; 1/36 ≈ 0.02778; 1/45 ≈ 0.02222; sum = 0.10.Find Rp: Rp = 1 / 0.10 = 10 kΩ.Add series R1: R_total = 7 kΩ + 10 kΩ = 17 kΩ. Verification / Alternative check: If you replace the three parallel resistors by 10 kΩ and measure the total with an ohmmeter across the two ends of the whole string, you would read approximately 17 kΩ, confirming the arithmetic. Why Other Options Are Wrong: 4 kΩ: Much too small; parallel of 20, 36, 45 kΩ cannot be below the smallest 20 kΩ by that much, and series with 7 kΩ would increase the total. 41 kΩ / 108 kΩ: These ignore the strong reduction due to the parallel branch and/or wrongly add all values. Common Pitfalls: Accidentally adding parallel resistances directly (incorrect) or forgetting to convert units consistently. Always compute the parallel equivalent first, then add series resistances. Final Answer: 17 kΩ

Question 19

Wheatstone bridge concept: When a Wheatstone bridge is balanced, what will an ideal center instrument (voltmeter/galvanometer) read across the bridge diagonal?

Accepted Answer

Introduction / Context: A Wheatstone bridge is widely used for precision measurement of resistance and for sensing applications (e.g., strain gauges). At balance, the bridge provides a null indication, which makes measurements highly accurate and immune to many error sources. Given Data / Assumptions: Four resistive arms forming a diamond (bridge) network. An ideal null detector (voltmeter/galvanometer) connected across the bridge diagonal. “Balanced” means R1/R2 = R3/R4. Concept / Approach: At balance, the potentials at the two midpoints are equal. With no potential difference between them, the detector sees zero volts. This null method lets you detect tiny changes by rebalancing, rather than reading an absolute voltage directly. Step-by-Step Solution: Define balance condition: R1/R2 = R3/R4.Equal ratios imply equal divider fractions; midpoints have the same potential.Therefore V_diagonal = 0 V → no current through the detector. Verification / Alternative check: Apply superposition or voltage divider equations to each leg; both midpoint voltages evaluate identically under balance, confirming zero differential. Why Other Options Are Wrong: Same/half/twice source voltage: A null detector reads zero at balance; any nonzero reading indicates imbalance. Common Pitfalls: Confusing “bridge output” with “source voltage” and overlooking that the bridge measures imbalance, not absolute level. Final Answer: zero volts

Question 20

In the given circuit, the Thevenin resistance equals 800 Ω.

Accepted Answer

False

Series-Parallel Circuits Questions