Electronics Engineering - Online Test
Q1. The force on a point charge +q kept at a distance d from the surface of an infinite grounded metal plate in a medium of permittivity 𝜖 i
Answer : Option C
Explaination / Solution:
Consider the point charge +q and infinite surface as shown below.
We can replace the image charge by a negative equivalent charge -q placed at
2d distance from +q charge
Hence, the force experienced by +q charge is
Q2.
Consider the frequency modulated signal 
with carrier frequency of 105 Hz. The modulation index is
with carrier frequency of 105 Hz. The modulation index is
Answer : Option B
Explaination / Solution:
Q3.
In a uniformly doped BJT, assume that NE, NB and NC are the emitter, base and collector doping in atoms/cm3, respectively. If the emitter injection efficiency of the BJT is close unity, which one of the following condition is TRUE
Answer : Option B
Explaination / Solution:
Emitter injection efficiency is given as
Q4. The following Karnaugh map represent a function F.
A minimized form of the function F is
Answer : Option B
Explaination / Solution:
No Explaination.
Q5. In the figure shown, all elements used are ideal. For time t<0, S1 remained closed and S2 open.
At t = 0, S1 is opened and S2 is closed. If the voltage Vc2 across the capacitor C2 at t = 0 is zero,
the voltage across the capacitor combination at t=0+ will be
Answer : Option C
Explaination / Solution:
Q6. In the following circuit, the input voltage Vin is 100
sin(100πt). For 100πRC = 50, the
average voltages across R (in volts) under steady-state is nearest to
Answer : Option C
Explaination / Solution:
Given circuit is voltage doubler
Vm = Voltage across each capacitor = 100V
Voltage across two capacitors (in steady state)
= 2Vm = 200V
Q7. Loop transfer function of a feedback system is 
Take the Nyquist contour in
the clockwise direction. Then, the Nyquist plot of G(s)H(s) encircles -1 + j0.
Take the Nyquist contour in
the clockwise direction. Then, the Nyquist plot of G(s)H(s) encircles -1 + j0.
Answer : Option A
Explaination / Solution:
Q8. A good current buffer has
Answer : Option B
Explaination / Solution:
No Explaination.
Q9. Let f(x) be a real, periodic function satisfying f(−x) = −f(x). The general form of its Fourier series representation would be
Answer : Option B
Explaination / Solution:
Q10. A magnetic field in air is measured to be 
What current distribution leads to this field ?
What current distribution leads to this field ?[Hint : The algebra is trivial in cylindrical coordinates.]
Answer : Option C
Explaination / Solution:
