GATE EC Mock Test 1 (20 Questions, Free)
A free GATE Electronics and Communication mock test with 20 original questions on networks, signals, devices, analog, digital, control, communications and EM.
This mock test has 20 original GATE-style questions across the electronics and communication syllabus. Give yourself 60 minutes, write your answers on paper, then open each question to check. Score +1 per correct answer and −1/3 per wrong MCQ.
Networks and signals
A series RLC circuit has R = 10 Ω, L = 1 mH and C = 1 µF. What is its quality factor at resonance?
Show answer and explanation
Answer: 3.16Q = (1/R)√(L/C) = (1/10)√1000 ≈ 3.16.
The impulse response of an LTI system is h(t) = e^(−2t) u(t). What is its DC gain H(0)?
Show answer and explanation
Answer: 0.5H(s) = 1/(s + 2), so H(0) = 1/2.
A 1024-point FFT (radix-2) needs how many complex multiplications, using (N/2) log₂ N?
Show answer and explanation
Answer: 5120(1024/2) × log₂ 1024 = 512 × 10 = 5120.
Which of these systems are linear? (Select all that apply.)
Show answer and explanation
Answer: A, BScaling and delay are linear. Squaring is not, and adding a constant breaks additivity (zero input gives non-zero output).
Devices and analog circuits
A BJT has collector current 2.6 mA and V_T = 26 mV. What is its transconductance in mA/V?
Show answer and explanation
Answer: 100g_m = I_C/V_T = 2.6 mA/26 mV = 100 mA/V.
A MOSFET in saturation has k = 2 mA/V², V_GS = 3 V and V_T = 1 V. Using I_D = (k/2)(V_GS − V_T)², what is I_D in mA?
Show answer and explanation
Answer: 4I_D = 1 × 2² = 4 mA.
An intrinsic semiconductor has n_i = 10¹⁰ cm⁻³. After doping, n = 10¹⁶ cm⁻³. What is the hole concentration in cm⁻³?
Show answer and explanation
Answer: 10000p = n_i²/n = 10²⁰/10¹⁶ = 10⁴ cm⁻³.
A non-inverting op-amp amplifier has R_f = 90 kΩ and R₁ = 10 kΩ. What is its gain?
Show answer and explanation
Answer: 10Gain = 1 + R_f/R₁ = 1 + 9 = 10.
An op-amp has gain–bandwidth product 1 MHz. What is the bandwidth in kHz when it is used with a closed-loop gain of 20?
Show answer and explanation
Answer: 50Bandwidth = GBW/gain = 1000 kHz/20 = 50 kHz.
Digital circuits
How many flip-flops are needed for a mod-12 counter?
Show answer and explanation
Answer: 42³ = 8 < 12 ≤ 16 = 2⁴: 4 flip-flops.
How many select lines does a 32:1 multiplexer have?
Show answer and explanation
Answer: 52⁵ = 32, so 5 select lines.
What is the output of an XOR gate with inputs A and B when A = B?
Show answer and explanation
Answer: AXOR is 1 only when the inputs differ, so A ⊕ A = 0.
Control systems
The characteristic equation s³ + 2s² + 3s + 10 = 0 has how many roots in the right half-plane?
Show answer and explanation
Answer: 2Routh column: 1, 2, (6 − 10)/2 = −2, 10. Two sign changes: two right-half-plane roots.
A unity-feedback system has G(s) = 9/(s(s + 3)). What is the natural frequency ω_n in rad/s of the closed loop?
Show answer and explanation
Answer: 3Closed loop 9/(s² + 3s + 9): ω_n = 3 rad/s.
Communications
A voice signal is sampled at 8 kHz with 8 bits per sample. What is the PCM bit rate in kbit/s?
Show answer and explanation
Answer: 64Bit rate = n × f_s = 8 × 8 = 64 kbit/s.
A source has symbols with probabilities 1/2, 1/4 and 1/4. What is its entropy in bits per symbol?
Show answer and explanation
Answer: 1.5H = 0.5 × 1 + 0.25 × 2 + 0.25 × 2 = 1.5 bits.
In AM with modulation index 0.5, what fraction of the total power is in the sidebands? (Give 3 decimal places.)
Show answer and explanation
Answer: 0.111Sideband share = (μ²/2)/(1 + μ²/2) = 0.125/1.125 ≈ 0.111.
Electromagnetics
A rectangular waveguide has a = 2.5 cm. What is the TE₁₀ cutoff frequency in GHz (c = 3 × 10⁸ m/s)?
Show answer and explanation
Answer: 6f_c = c/(2a) = 3 × 10⁸/0.05 = 6 GHz.
A line with Z₀ = 50 Ω is terminated in 50 Ω. The reflection coefficient is:
Show answer and explanation
Answer: AΓ = (50 − 50)/(50 + 50) = 0: a matched load reflects nothing.
A plane wave travels in a lossless medium with ε_r = 4 and μ_r = 1. What is its speed in units of 10⁸ m/s?
Show answer and explanation
Answer: 1.5v = c/√(ε_r μ_r) = 3 × 10⁸/2 = 1.5 × 10⁸ m/s.
Your score
| Score (out of 20) | What it means |
|---|---|
| 16 and above | Strong: move to full-length papers |
| 10 – 15 | Revise the subjects where you lost marks |
| Below 10 | Go back to the lessons, then retake after two weeks |
Revise with the formula sheet and follow the study plan.