The GATE Grind

GATE 2014 EE (EE1) – Question 18

Electric Circuits · Transient response of DC and AC networks, sinusoidal steady-state analysis, resonance, two port networks, balanced three phase circuits, star-delta transformation, complex power and power factor in AC circuits · 1 mark · Multiple choice

A 1 µF capacitor with initial voltage v_C(0) = −2 V is in series with 100 Ω and connected to an ideal 20 mA DC current source by operating both switches at t = 0, as shown. Which graph approximates source voltage v_s over the next few seconds?

Diagram for GATE 2014 EE (EE1) question 18
  1. Graph A
  2. Graph B
  3. Graph C
  4. Graph D

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (C) Graph C

Explanation

The ideal source enforces i=20mA, giving resistor drop iR=2V and capacitor slope dvC/dt=i/C=20000V/s. Initially vC=−2V, so vS(0+)=vC+iR=0. Thus vS(t)=20000t, a straight ramp starting at zero, **C**. A constant-current source produces linear charging, not an exponential.