Diffusion Capacitance Definition C d = dQ / dV Where: Q = stored charge V = applied voltage Physical Meaning Occurs in forward-biased PN junctions Charge carriers accumulate instead of disappearing instantly This stored charge behaves like capacitance More current → more stored charge → higher capacitance Mathematical Derivation Stored charge: Q = I × τ Differentiating: C d = dQ/dV = d(Iτ)/dV Assuming τ is constant: C d = τ (dI/dV) Using Diode Equation I = I s e^(V / ηV T ) Differentiating: dI/dV = I / (ηV T ) Final Formula C d = τI / (ηV T ) Key Insights Diffusion capacitance increases with current Important in forward bias Usually larger than junction capacitance in forw...

  Thyristor dv/dt Capacitance Calculation Thyristor dv/dt Capacitance Calculation Given Data dv/dt = 200 V/μs = 200 × 10 6 V/s Forward breakover current I = 5 mA = 5 × 10 -3 A Key Formula I = C (dV/dt) Step: Solve for Capacitance C = I / (dV/dt) Substitute Values C = (5 × 10 -3 ) / (200 × 10 6 ) Calculation C = (5 / 200) × 10 -9 C = 0.025 × 10 -9 C = 2.5 × 10 -11 F Final Answer C = 25 pF option A This represents the effective junction/diffusion capacitance High dv/dt can generate current large enough to trigger the thyristor Snubber circuits (RC) are used to limit dv/dt This prevents false triggering of thyristors

  RL Circuit Inductor Calculation RL Circuit Inductor Calculation Given Data Supply voltage V = 250 V Frequency f = 400 Hz Load current I DC = 100 A Load resistance R = 0.5 Ω Allowed ripple = 15% Step 1: Ripple Current I ripple = 0.15 × 100 = 15 A Step 2: Ripple Voltage Approximation: V r ≈ 250 V Step 3: RL Ripple Formula I ripple = V r / √(R² + (ωL)²) Rearranging: √(R² + (ωL)²) = V r / I ripple R² + (ωL)² = (250 / 15)² Step 4: Solve 250 / 15 = 16.67 R² = (0.5)² = 0.25 (ωL)² = 16.67² − 0.25 (ωL)² ≈ 277.8 − 0.25 = 277.55 ωL ≈ √277.55 ≈ 16.66 Step 5: Find Inductance ω = 2πf = 2π × 400 ≈ 2513 L = 16.66 / 2513 L ≈ 0.00663 H Final Answer L ≈ 6.6 mH ...

  Total Charge with Variable Density Total Charge on Sphere (Variable Density) Given Radius R = 30 cm = 0.3 m Charge density: ρ(r) = 200 (r / R) pC/m³ Step 1: Convert to SI Units ρ(r) = 200 × 10 -12 × (r / R) Step 2: Use Charge Formula Q = ∫₀ᴿ ρ(r) · 4πr² dr Step 3: Substitute Q = ∫₀ᴿ (200 × 10 -12 × r/R) · 4πr² dr Step 4: Simplify Q = (200 × 10 -12 × 4π / R) ∫₀ᴿ r³ dr Step 5: Integrate ∫ r³ dr = r⁴ / 4 Q = (200 × 10 -12 × 4π / R) × (R⁴ / 4) Step 6: Simplify Q = 200π × 10 -12 × R³ Step 7: Substitute R = 0.3 R³ = (0.3)³ = 0.027 Q = 200π × 10 -12 × 0.027 Q = 5.4π × 10 -12 Final Answer: Q ≈ 1.7 × 10 -11 C Or, 17 pC Option A

  Z-Parameters of Lattice Network Z-Parameters of a Lattice Network Lattice Network Setup A lattice network typically has two diagonal impedances: Za (one diagonal) Zb (the other diagonal) The Easy Trick z11 = z22 = (Za + Zb) / 2 z12 = z21 = (Zb - Za) / 2 How to Remember It Sum → diagonal terms → divide by 2 Difference → off-diagonal terms → divide by 2 Add → self impedance (z11, z22) Subtract → mutual impedance (z12, z21) z = (1/2) × [ (Za + Zb) (Zb - Za) (Zb - Za) (Za + Zb) ] Symmetry shows: z11 = z22 z12 = z21 When This Works Standard symmetric lattice network ...

  Minimum Slew Rate of Op-Amp Minimum Slew Rate of Op-Amp What is Slew Rate? Slew rate is the maximum rate of change of output voltage of an op-amp. SR = dV / dt (V/μs) Minimum Slew Rate Formula To avoid distortion: SR min = 2π f V peak f = frequency of signal V peak = peak output voltage Why This Matters If slew rate is too low, output cannot follow input Signal becomes distorted (triangular instead of sine) Example Given: f = 20 kHz V peak = 10 V SR min = 2π × 20000 × 10 ≈ 1.26 V/μs Required slew rate ≥ 1.26 V/μs Typical Values General-purpose op-amp (LM741): ~0.5 V/μs Audio op-amps: 5–20 V/μs High-speed op-amps: 100+ V/μs Summary The minimum slew rate depends on signal freq...

  Choke Input Filter Choke Input Filter A well-designed choke input filter is a type of power supply filter used to smooth the output of a rectifier (like in DC power supplies). It uses an inductor (choke) as the first component right after the rectifier, followed by a capacitor. Basic Structure Rectifier → Choke (L) → Capacitor (C) → Load What Makes It Well-Designed? Critical Inductance is satisfied: The choke must have enough inductance to keep current flowing continuously. This minimum value is called critical inductance. Low ripple output: A good design significantly reduces AC ripple in the DC output. The choke resists sudden changes in current. Proper load current: Works best when the load current is above a certain minimum level. Too light a load results in poor filter...

    UGC-NET Electronic Science Question Paper With Answer Key and Full Explanation [Dec 2024] UGC-NET Electronic Science Question Paper With Answer Key Download Pdf [Dec 2024 / Jan 2025] (Exam held 27-01-2025) Download Question Paper                  2025 | 2024 | 2023 | 2022 | 2021 | 2020 UGC-NET Electronic Science  Jan 2025 Answers with Explanations Q.1 Answer. Option (3) Q.2 Answer. Option (3) Q.3 Answer. Option (3) Q.4 Answer. Option (4) Q.5 Answer. Option (3) Q.6 Answer. Option (3) Q.7 Answer. Option (4) Q.8 Answer. Option (3) Q.9 Answer. Option (3) Q.10 Answer. Option (4) Q.11 Answer. Option (3) solution hint: 20*0.8 = 16KW ; 16/0.85 = 18.82 Q.12 Answer. Option (2) solution hint: E = V/d; j=epsilon*dE/dt Q.13 Answer. Option (3) Q.14 Answer. Option (3) Q.15 Answer. Option (2) solution hint: 1/2*pi*r Q.16 Answer. Option (3) solution hint: 1/RC Q.17 Answer. Option (3) Q.18 Answer. Option (2) solution hint: Fto...