AFCAT (Air Force Common Admission Test) EKT - Computer Science and Electronics Stream Syllabus

EKT - Computer Science and Electronics 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 - Computer Science and Electronics Stream in AFCAT (Air Force Common Admission Test), not a summary of it.

1. 1

   Analog and Digital Electronics

   3 topics

   • Semiconductor devices
     • Diodes, BJTs and FETs
     • Rectifiers and amplifiers
   • Digital logic design
     • Logic gates and Boolean algebra
     • Combinational and sequential circuits
   • Operational amplifiers and applications
2. 2

   Communication and Signal Systems

   4 topics

   • Analog and digital modulation
     • AM, FM and PM
     • PCM and digital modulation schemes
   • Signals and systems
   • Antennas and wave propagation
   • Microwave and radar fundamentals
3. 3

   Control Systems and Instrumentation

   3 topics

   • Time and frequency response analysis
   • Stability and feedback systems
   • Transducers and measurement
4. 4

   Computer Science Fundamentals

   4 topics

   • Programming and data structures
     • C/C++ programming
     • Arrays, linked lists, trees and graphs
   • Microprocessors and microcontrollers
   • Computer networks and operating systems
   • Database management basics

EKT - Computer Science and Electronics Stream flashcards for AFCAT (Air Force Common Admission Test)

21 of 51 cards from the EKT - Computer Science and Electronics Stream deck — real questions with worked answers.

1. In a PN junction diode, what is the typical forward voltage drop (cut-in/threshold voltage) for silicon and germanium diodes?

   Silicon: about 0.7 V; Germanium: about 0.3 V.

2. What is the difference between a Zener diode and an avalanche breakdown diode in terms of operation and temperature coefficient?

   Zener breakdown dominates below ~5 V (negative temperature coefficient); avalanche breakdown dominates above ~6 V (positive temperature coefficient). Zener diodes operate in reverse breakdown to provide voltage regulation.

3. Name the three regions of operation of a BJT and the junction bias conditions for each.

   Cutoff: both junctions reverse biased. Active: emitter-base forward, collector-base reverse. Saturation: both junctions forward biased.

4. What is the relationship between the BJT current gains alpha and beta?

   beta = alpha / (1 - alpha), and alpha = beta / (1 + beta). Also IC = beta*IB and IC = alpha*IE.

5. How does an enhancement-mode N-channel MOSFET conduct, and what is the condition on VGS?

   It conducts when VGS exceeds the threshold voltage Vth (VGS > Vth), forming an inversion channel; it is normally OFF with no channel at VGS = 0.

6. State De Morgan's two theorems in Boolean algebra.

   (A·B)' = A' + B' and (A + B)' = A'·B'. The complement of a product is the sum of complements, and vice versa.

7. Which logic gates are called universal gates and why?

   NAND and NOR gates, because any Boolean function (AND, OR, NOT) can be implemented using only NAND gates or only NOR gates.

8. What is the difference between a combinational and a sequential logic circuit?

   Combinational circuits' outputs depend only on present inputs (no memory), e.g., adders, multiplexers. Sequential circuits' outputs depend on present inputs and past states (have memory/clock), e.g., flip-flops, counters.

9. What is the characteristic (excitation) behavior of a JK flip-flop for J=1, K=1?

   The output toggles (Q_next = Q'). For J=0,K=0 it holds; J=1,K=0 sets (Q=1); J=0,K=1 resets (Q=0).

10. How many flip-flops are needed to build a MOD-N counter?

    The minimum number n of flip-flops satisfies 2^n >= N (n = ceil(log2 N)).

11. What is the ideal voltage gain expression for a non-inverting op-amp amplifier?

    Av = 1 + (Rf / Rin), where Rf is the feedback resistor and Rin is the resistor from the inverting input to ground.

12. What is the ideal voltage gain of an inverting op-amp amplifier?

    Av = - (Rf / Rin); the output is inverted (180 degrees out of phase) and the inverting input acts as a virtual ground.

13. State the two 'golden rules' (ideal assumptions) for an op-amp with negative feedback.

    1) No current flows into the input terminals (infinite input impedance). 2) The voltage difference between the two inputs is zero (virtual short).

14. What is the output of an ideal op-amp integrator, and what component configuration creates it?

    Vout = -(1/RC) * integral of Vin dt. It uses a resistor at the input and a capacitor in the feedback path of an inverting op-amp.

15. Define CMRR (Common Mode Rejection Ratio) for an op-amp and its ideal value.

    CMRR = differential gain / common-mode gain (often in dB: 20 log10). Ideally it is infinite, meaning the op-amp completely rejects signals common to both inputs.

16. What is the modulation index for AM, and what range avoids distortion (overmodulation)?

    Modulation index m = Em/Ec (message amplitude / carrier amplitude). It must satisfy 0 < m <= 1; m > 1 causes overmodulation and distortion.

17. What is the total transmitted power in an AM wave in terms of carrier power Pc and modulation index m?

    Pt = Pc (1 + m^2/2). At m=1, Pt = 1.5*Pc, with two-thirds of the power in the carrier and one-third in the sidebands.

18. Compare AM and FM in terms of noise immunity and bandwidth.

    FM has better noise immunity (amplitude noise is removed by limiters) but requires larger bandwidth. AM is simpler and uses less bandwidth but is more susceptible to noise.

19. What is Carson's rule for estimating FM bandwidth?

    BW = 2(delta_f + fm), where delta_f is the peak frequency deviation and fm is the highest modulating frequency.

20. Compare ASK, FSK, and PSK digital modulation schemes by what carrier parameter they vary.

    ASK varies amplitude, FSK varies frequency, PSK varies phase of the carrier according to the digital data.

21. State the Nyquist sampling theorem.

    A band-limited signal with maximum frequency fm can be perfectly reconstructed if the sampling rate fs >= 2*fm. 2*fm is the Nyquist rate.

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