Electrical Machine MCQ Challenge 2026 | Day 2 | DC Machines & Transformers | JE AE Exams

Main ideas & lessons conveyed

Preparation strategy (2026 exam “new pattern”)

• The teacher runs a 21-day challenge focused on DC machines and transformers, aiming for 10,000 questions total.
  • Approx. 2100 questions in 21 days (≈ 100 questions/day during the session).
• Daily plan inside the challenge/day:
  1. Do PYQs first (previous year questions) to build confidence.
  2. Then attempt new-pattern questions (2026) for concept + practice variety.
  3. Later, mix theory + numericals + conceptual questions, with an explicit note that the exam includes both conceptual and numerical questions.

Question types emphasized

Repeated formats commonly seen in competitive exams:

• MCQs (A/B/C/D)
• Assertion–Reason questions
  • The teacher repeatedly warns to evaluate assertion and reason separately.
• Match the following / correct pair
• Sequence arranging (especially in energy conversion)
• Direct conceptual questions, such as:
  • efficiency conditions
  • transformer parts
  • winding types

Core transformer / MCQ concepts highlighted

• Transformer oil purpose: provides insulation and cooling.
• Transformer efficiency (power transformer): approximately ~95%
  • Distribution transformer: lower, around ~80–85%
• No rotating parts in transformers → contributes to high efficiency.
• Parallel transformers load sharing: determined by the impedance ratio, affecting current/ratings sharing (explained via a “current division rule”-type approach).
• Maximum efficiency condition for a transformer:
  • efficiency is maximum when copper loss = iron loss, i.e., (P_c = P_i).
• No-load / open-circuit test:
  • used to determine iron loss
  • assumes no-copper-loss at no-load.
• Transformer buzzing/sparking-type phenomenon:
  • Buzzing attributed mainly to magnetostriction (mechanical vibration due to magnetization/demagnetization).
  • Also mentions possible dielectric / partial discharge causes.
• Transformer rating choice:
  • transformer ratings are given in kVA, not kW, because:
    • iron loss depends mainly on voltage
    • copper loss depends mainly on current
  • (Thus rating is tied closely to current/voltage behavior rather than pure real power.)

Core DC machine concepts highlighted

• Yoke’s role:
  • provides mechanical support
  • offers a low reluctance flux path.
• Commutator role:
  • used in generators to convert AC to DC
  • in motors to reverse armature current direction
  • constructed using copper segments with insulation (teacher mentions mica).
• Brushes:
  • support/complement commutation and collect/supply current.
• Pole & armature functions:
  • poles spread flux
  • armature conductors carry current and participate in flux linkage.
• Wave winding generator EMF numericals:
  • uses the standard EMF relation involving:
    • p (number of poles)
    • Φ (flux per pole)
    • n (speed)
    • Z (total conductors)
    • and parallel paths (A).
• Simplex winding assertion–reason
  • reasoning focuses on number of parallel paths
  • notes general trends/traps in assertion–reason wording (including preferences like high voltage / low current machines).
• Armature reaction:
  • armature current produces its own flux that opposes/disturbs the main field flux.
  • mentions:
    • leading/trailing pole tips
    • crowding effect
    • increased saturation/loss and sparking analogy.
• Neutral plane shift cause:
  • attributed practically to armature reaction.
• Voltage regulation / terminal voltage drop mechanisms:
  • generator terminal voltage drop mainly due to:
    • armature resistance drop
    • armature reaction
• Additional conceptual reminders
  • Voltage regulation can be negative under leading power factor (capacitive load) (teacher emphasized this repeatedly).
  • In transformers, frequency remains unchanged, while voltage/current change.
  • Core purpose:
    • reduces reluctance of the magnetic circuit
    • lamination reduces eddy current loss
    • core material reduces hysteresis loss

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Methodology / instructions presented

How the teacher structures practice

• Start with PYQs from DC machines & transformers.
• Use rapid A/B/C/D MCQs to:
  • build speed
  • improve exam-style familiarity
  • reinforce memory via repetition
• After PYQs, move to new pattern (2026) questions from DC machine topics.
• Use a recurring “mix” approach:
  • Conceptual questions: target ~20%
  • New variety questions: ~30–40%
  • Include numericals alongside

How to approach Assertion–Reason questions

• Read Assertion and Reason independently first.
• Do not assume the reason automatically explains the assertion.
• Select the option based on:
  • whether assertion is true/false
  • whether reason is true/false
  • and whether the reason actually supports the assertion
  • (The teacher repeatedly warns about this.)

General exam strategy implied

Don’t panic—don’t run away or stop—if something feels slightly off. Maintain pace, switch questions frequently, and continue through the session window (mentioned: 9:00–10:00).

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Speakers / sources featured

Primary speaker/host

• R. A. Sharma (RA Sharma ji) (referred to repeatedly as “sir” / “R A Sharma ji”)

Institutions/platforms mentioned

• Creative Institute, Janjgir
• Telegram channel
  • used for PDF notes, class schedules, registrations, and test series updates
• Education Now app
  • mentioned for course access/discount

Students/commenters mentioned (credited as answering correctly)

• Ashish Sahu, Gaurav Nishad, Kishan Sakshi, Krishna Kumar, Vinay, Akhil Thakur, Deepak Soni, Lata Sahu, Om Prakash, Chotel Sahu, Sakshi Patel, Gauri Shankar Soni, Kiran Sahu, Gauri Shankar