Practice Test GeeksBEE - Bachelor of Electrical Engineering Practice Test
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Electrical Machines Flashcards

7 cards from real BEE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A transformer has 200 primary turns and 400 secondary turns. If the primary voltage is 120V, what is the secondary voltage?

    Answer: 240V

    By the turns ratio formula V2/V1 = N2/N1, so V2 = 120 × (400/200) = 240V.

  2. The efficiency of a transformer reaches its maximum when:

    Answer: Iron losses equal copper losses

    Maximum efficiency occurs at the load where variable copper losses equal the constant iron (core) losses.

  3. In a DC motor, the back EMF (Eb) is related to supply voltage (V), armature current (Ia), and armature resistance (Ra) by:

    Answer: Eb = V - IaRa

    Applying KVL around the armature circuit gives V = Eb + IaRa, so Eb = V - IaRa.

  4. The synchronous speed of a 4-pole induction motor operating on a 60 Hz supply is:

    Answer: 1800 RPM

    Synchronous speed Ns = 120f/P = 120 × 60 / 4 = 1800 RPM.

  5. At synchronous speed, the slip of a three-phase induction motor is:

    Answer: 0

    Slip s = (Ns - Nr)/Ns; when rotor speed Nr equals synchronous speed Ns, slip equals zero.

  6. Which type of DC motor provides the highest starting torque and is most suitable for traction (railway) applications?

    Answer: DC series motor

    A DC series motor produces torque proportional to the square of armature current, giving very high starting torque at low speeds.

  7. The speed regulation of a DC shunt motor compared to a DC series motor is:

    Answer: Much better (lower regulation)

    The DC shunt motor maintains nearly constant speed from no-load to full-load, giving it excellent (low) speed regulation compared to the series motor.