AFCAT (Air Force Common Admission Test) EKT - Electrical and Mechanical Engineering Stream Syllabus

EKT - Electrical and Mechanical Engineering Stream syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for EKT - Electrical and Mechanical Engineering Stream in AFCAT (Air Force Common Admission Test), not a summary of it.

1. 1

   Electrical Circuits and Networks

   3 topics

   • Network theorems
     • Thevenin, Norton and superposition
   • AC and DC circuit analysis
   • Resonance and transients
2. 2

   Electrical Machines and Power Systems

   4 topics

   • DC machines
   • Transformers
   • Induction and synchronous machines
   • Power generation, transmission and distribution
3. 3

   Power Electronics and Drives

   3 topics

   • Power semiconductor devices
     • SCR, IGBT and MOSFET
   • Converters and inverters
   • Electric drives
4. 4

   Measurements and Manufacturing Processes

   3 topics

   • Electrical and electronic measurements
   • Casting, welding and forming
   • Machining and metrology

EKT - Electrical and Mechanical Engineering Stream flashcards for AFCAT (Air Force Common Admission Test)

21 of 54 cards from the EKT - Electrical and Mechanical Engineering Stream deck — real questions with worked answers.

1. State Thevenin's theorem.

   Any linear two-terminal network of voltage/current sources and resistances can be replaced by a single voltage source Vth (open-circuit voltage) in series with a single resistance Rth (resistance seen from the terminals with all independent sources deactivated).

2. State Norton's theorem and how Norton's equivalent relates to Thevenin's.

   Any linear two-terminal network can be replaced by a current source IN (short-circuit current) in parallel with a resistance RN. RN = Rth, and IN = Vth / Rth.

3. State the Maximum Power Transfer theorem for a DC resistive network.

   Maximum power is delivered to the load when the load resistance equals the Thevenin (source) resistance, RL = Rth. The maximum power delivered is Pmax = Vth^2 / (4·Rth), and efficiency at this point is only 50%.

4. State the Superposition theorem and its key limitation.

   In a linear network with multiple independent sources, the response in any element is the algebraic sum of responses caused by each source acting alone (others deactivated: voltage sources shorted, current sources opened). It applies only to linear quantities (V, I), NOT to power, because power is nonlinear (I^2R).

5. State Kirchhoff's Current Law (KCL) and Voltage Law (KVL).

   KCL: the algebraic sum of currents entering a node equals zero (charge conservation). KVL: the algebraic sum of voltages around any closed loop equals zero (energy conservation).

6. State the Reciprocity theorem.

   In a single-source linear bilateral network, the ratio of excitation to response is constant when the positions of excitation and response are interchanged. The current is unchanged if the voltage source and the response ammeter are swapped.

7. State Millman's theorem.

   Several parallel voltage sources V1,V2,... with series conductances G1,G2,... can be replaced by one equivalent source Veq = (ΣVk·Gk)/(ΣGk) in series with Req = 1/(ΣGk).

8. For a pure inductor and a pure capacitor in AC, what is the phase relationship between voltage and current?

   Inductor: current LAGS voltage by 90° (V leads I). Capacitor: current LEADS voltage by 90° (V lags I). Mnemonic: ELI the ICE man.

9. Define impedance and give the impedance of R, L and C in AC circuits.

   Impedance Z is the total opposition to AC (Z = V/I, complex). Resistor: ZR = R. Inductor: ZL = jωL. Capacitor: ZC = 1/(jωC) = -j/(ωC).

10. Define power factor and write the three powers in an AC circuit.

    Power factor = cosφ = P/S (ratio of real to apparent power). Real (active) power P = VI·cosφ (W); Reactive power Q = VI·sinφ (VAR); Apparent power S = VI (VA), with S^2 = P^2 + Q^2.

11. In a series RLC circuit, what is the condition for resonance and the resonant frequency?

    At resonance XL = XC, so the net reactance is zero, impedance is minimum (= R), and current is maximum and in phase with the supply. Resonant frequency f0 = 1/(2π√(LC)).

12. Define the quality factor (Q) of a series RLC circuit and its significance.

    Q = ω0L/R = 1/(ω0CR) = (1/R)√(L/C). It measures sharpness/selectivity of resonance and the voltage magnification across L or C. Bandwidth = f0/Q; high Q = narrow, selective response.

13. How does a parallel (tank) RLC circuit behave at resonance compared to a series circuit?

    At parallel resonance the impedance is MAXIMUM (purely resistive, the 'dynamic resistance' L/CR), and the line current is MINIMUM. This contrasts with series resonance where impedance is minimum and current maximum. It is called a rejector circuit.

14. Write the time constant of an RC and an RL circuit and what it physically means.

    RC time constant τ = RC; RL time constant τ = L/R. τ is the time for the transient to reach about 63.2% of its final change (or decay to 36.8%). After ~5τ the transient is essentially complete.

15. During transients, how do an inductor and a capacitor behave at t=0+ and at steady state?

    Inductor: current cannot change instantly, so at t=0+ it acts as an open circuit (if initially de-energized); at DC steady state it acts as a short. Capacitor: voltage cannot change instantly, so at t=0+ it acts as a short (if uncharged); at DC steady state it acts as an open circuit.

16. What is the EMF equation of a DC machine?

    E = (φ·Z·N·P) / (60·A), where φ = flux per pole, Z = total armature conductors, N = speed in rpm, P = number of poles, A = number of parallel paths (A = P for lap winding, A = 2 for wave winding).

17. Differentiate lap winding and wave winding in DC machines.

    Lap winding: number of parallel paths A = P (= number of poles), used for high-current, low-voltage machines, needs P brush sets. Wave winding: A = 2 always, used for high-voltage, low-current machines, needs 2 brush sets.

18. What is back EMF in a DC motor and why is it important?

    Back EMF (Eb = V - Ia·Ra) is the voltage induced in the armature opposing the supply as the motor rotates. It automatically regulates armature current with load: Ia = (V - Eb)/Ra, making the motor self-regulating. At starting Eb = 0, so starting current is dangerously high (hence a starter is needed).

19. Compare the speed-torque characteristics of DC series and shunt motors.

    Series motor: high starting torque, speed varies inversely with load (runs dangerously fast at no load), used in traction/cranes. Shunt motor: nearly constant speed regardless of load, moderate starting torque, used where constant speed is needed (lathes, fans).

20. What is armature reaction in a DC machine and its effects?

    Armature reaction is the distortion/weakening of the main field flux by the magnetic field of the armature current. Effects: shifts the magnetic neutral axis (in motor, against rotation), demagnetizes (reduces flux), and causes sparking at the brushes. Remedied by interpoles and compensating windings.

21. What is the EMF equation of a transformer?

    E = 4.44·f·N·φm = 4.44·f·N·Bm·A, where f = frequency, N = number of turns, φm = maximum flux, Bm = max flux density, A = core area. This applies to both primary and secondary with their respective turns.

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