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GATE ECE GATE ECE — Core — practice questions

Explore 26 free GATE ECE — Core questions in GATE ECE Electronics & Communication. Open each question or exercise to read its content, reference answers and available explanation.

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GATE ECE — Core questions and exercises with answers

Showing questions 1–26 of 26.

In an intrinsic semiconductor at room temperature, the concentration of electrons equals:Read the answer and worked solution →In an n-type semiconductor, majority carriers are:Read the answer and worked solution →Mass-action law in semiconductors:Read the answer and worked solution →Energy gap of silicon at 300 K is approximately:Read the answer and worked solution →Zener diode is operated in:Read the answer and worked solution →BJT transistor terminals are:Read the answer and worked solution →Common-emitter current gain β (or h_FE):Read the answer and worked solution →In NMOS enhancement mode, drain current I_D in saturation:Read the answer and worked solution →For inverting amplifier (R_in to inv input, R_f feedback): voltage gain:Read the answer and worked solution →For non-inverting amplifier (input to + terminal, R_in & R_f resistor divider): gain:Read the answer and worked solution →NAND gate truth table: output is 0 when:Read the answer and worked solution →De Morgan's theorem:Read the answer and worked solution →Number of select lines for a 16:1 multiplexer:Read the answer and worked solution →Decimal 13 in binary:Read the answer and worked solution →Convert binary 10110 to decimal:Read the answer and worked solution →In 2's complement representation, range of 8-bit number:Read the answer and worked solution →Fourier transform of a delta function δ(t):Read the answer and worked solution →Transfer function 1/(s² + 2s + 5) has poles at:Read the answer and worked solution →In AM (amplitude modulation), modulating signal varies:Read the answer and worked solution →FM (frequency modulation) varies:Read the answer and worked solution →Shannon channel capacity:Read the answer and worked solution →Characteristic impedance of a lossless transmission line:Read the answer and worked solution →VSWR (Voltage Standing Wave Ratio) for matched load (R_L = Z_0):Read the answer and worked solution →Wave equation in vacuum (Maxwell):Read the answer and worked solution →Cutoff frequency of RC low-pass filter:Read the answer and worked solution →For n-bit ADC with full-scale V_FS, resolution (LSB) is:Read the answer and worked solution →

Worked practice questions

In an intrinsic semiconductor at room temperature, the concentration of electrons equals:

  1. Number of donors
  2. Number of atoms
  3. Zero
  4. Concentration of holes (n = p = n_i)
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Correct answer: D. Concentration of holes (n = p = n_i)

**Intrinsic semiconductor:** pure, no dopants. Thermal excitation creates electron-hole pairs in equal numbers. n = p = n_i (intrinsic carrier concentration). **For Si at 300K:** n_i ≈ 1.5 × 10¹⁰ /cm³.

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In an n-type semiconductor, majority carriers are:

  1. Both equal
  2. Electrons (donor atoms like P, As donate free electrons)
  3. Ions
  4. Holes
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Correct answer: B. Electrons (donor atoms like P, As donate free electrons)

n-type: doped with pentavalent (P, As, Sb). Donor atoms contribute extra electrons. **Majority:** electrons (n >> p). Minority: holes. Conductivity dominated by electron motion.

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Mass-action law in semiconductors:

  1. n = p
  2. n + p = constant
  3. n × p = n_i² (regardless of doping)
  4. n - p = 0
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Correct answer: C. n × p = n_i² (regardless of doping)

**Law of mass action:** n × p = n_i² (constant at given temperature). **For n-type:** n ≈ N_d, p = n_i²/N_d (small). **For p-type:** p ≈ N_a, n = n_i²/N_a. Independent of doping level.

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