DC Motors – Verified PYQ Authority Guide
DC Motors is organised as a topic-level PYQ authority page. It brings together the strongest verified question clusters, exam/year coverage and concept-level practice so students can revise the topic without jumping through unrelated notes. Every factual learning cue below is drawn from the existing verified, published and approved English PYQ corpus or from its Knowledge Graph relationships; the hub does not invent unsupported technical claims.
PYQ evidence snapshot
3 verified PYQs are currently mapped to this Topic hub. The represented years include 2026, 2025. Exam coverage currently includes Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2,, Assistant Engineer (Electrical), Class-2, Road and Building Department. Subject context includes Electrical Engineering. These values come from live mappings and can expand automatically when new verified PYQs are added.
Most useful verified PYQs to solve first
Start with the actual questions rather than memorising a generic note. The links below are ranked from the mapped corpus using repeat history and editorial quality, while the complete explanation stays on the individual question page.
- A DC motor has flux = constant and armature current = 20 A. 1. Torque is directly proportional to armature current under constant flux condition. 2. If current doubles, torque also doubles.…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · DC Motor Torque and Armature Current
The electromagnetic torque of a DC motor is proportional to the product of air-gap flux and armature current. If flux is held constant, torque… - A DC motor is supplied with 220 V and draws an armature current of 10 A. The armature resistance is 1 Ω. Then 1. The back EMF developed in the motor is…
Deputy Executive Engineer (Electrical), Class-2, Sports Authority of Gujarat / Assistant Engineer (Electrical), Class-2, · 2026 · DC Motor Back EMF and Converted Power
In a DC motor, back EMF is generated by armature rotation and opposes the applied supply. Eb=V−IaRa=220−10×1=210 V. Converted electromagnetic power≈EbIa=210×10=2100 W. Key relation:… - _________ test is used for determining the efficiency of a traction motor.
Assistant Engineer (Electrical), Class-2, Road and Building Department · 2025 · Field Test
The field test is a regenerative/back-to-back test suited to DC series machines, including traction motors, and allows efficiency to be determined under load conditions…
Formula & key-relationship bank from verified solutions
T=kΦI_a.E_b=V−I_aR_a; P_converted≈E_b I_a; T∝ΦI_a.Regenerative test principle: Supply input ≈ combined losses of the two machines Efficiency is obtained from measured losses and machine output/input.
Use these as revision triggers and open the linked PYQ before applying a formula numerically; variable definitions and assumptions belong to the exact solved question.
Core ideas repeatedly reinforced by the solved corpus
- The electromagnetic torque of a DC motor is proportional to the product of air-gap flux and armature current. If flux is held constant, torque varies directly with armature current, so doubling current ideally doubles torque. Key relation: T=kΦI_a.…
- In a DC motor, back EMF is generated by armature rotation and opposes the applied supply. Eb=V−IaRa=220−10×1=210 V. Converted electromagnetic power≈EbIa=210×10=2100 W. Key relation: E_b=V−I_aR_a; P_converted≈E_b I_a; T∝ΦI_a. Exam focus: Higher load → initially lower speed/Eb → higher…
- The field test is a regenerative/back-to-back test suited to DC series machines, including traction motors, and allows efficiency to be determined under load conditions without wasting full output power.
Exam tips already validated in SRO solutions
- Constant flux converts the general torque equation into T∝I_a.
- Higher load → initially lower speed/Eb → higher armature current.
- Match the test method to the DC motor connection type.
Common mistakes to avoid
- Do not generalize constant-flux behavior into 'torque is independent of flux'.
- Do not say Eb rises simply because load current rises at constant supply.
- Do not select Swinburne's test for a series traction motor; no-load operation of a series motor is unsafe.
Topic and concept coverage
Mapped topic labels include DC Motors. The concept trail includes DC Motor Back EMF and Converted Power, DC Motor Torque and Armature Current, Field Test. Use these labels as a revision map: move from the broad area to the narrow concept, solve a verified PYQ, inspect the detailed reasoning, and then attempt another question from the same cluster.
Knowledge Graph navigation
Continue with Electrical Machines, Back EMF, Testing of DC Series Motors, Torque Equation, Electrical Engineering, DC Motor Back EMF and Converted Power, DC Motor Torque and Armature Current, Field Test. These are canonical SRO entity links based on the Knowledge Graph and shared question mappings, not keyword-stuffed tag pages.
How to revise this authority page efficiently
- Solve before reading: answer a mapped PYQ first.
- Read the exact explanation: verify the correct principle, formula, distractor logic and common mistake on that question page.
- Move one level in the graph: use the closest concept/sub-topic/topic link rather than opening unrelated content.
- Reattempt: solve another verified PYQ from this hub and check whether the same error repeats.
Quality scope: this page is automatically maintained from SRO’s verified mapped corpus. It enriches one canonical authority URL instead of generating multiple near-duplicate pages for keyword variants. Manual authority articles are never overwritten by the automated engine.