Quiz Electronics Engineering 11 Aug 2020

Quiz Electronics Engineering
Exam: NIC
Topic: Miscellaneous
Date: 11/08/2020

Each Question carries 1 Mark
Negative Marking: 1/4
Time: 10 Minutes

Q1. A SCR triggered by a current pulse through its gate can be turned off by
(a) by reversing the polarity of anode and cathode voltage.
(b) by giving pulse to the cathode.
(c) by giving pulse to anode.
(d) giving another pulse of the same polarity to the gate.

Q2. The ASCII is –
(a) a four bit input output code
(b) a two bit input output code
(c) a seven bit input output code
(d) an eight bit input output code

Q3. For 200 V r.m.s. value triangular wave, the peak voltage will be
(a) 150 V
(b) 200 V
(c) 260 V
(d) 346 V

Q4. What type of temperature coefficient do thermistors have?
(a) Positive
(b) Negative
(c) Either positive or negative
(d) None of these

Q5. The angle for which there is no reflection and the incident wave is vertically polarized, is known as
(a) reflection angle
(b) steradian angle
(c) Brewster angle
(d) none of the above

Q6. Which one of the following is the correct relation?
(a) F(at) ⟷ aF(ω/a)
(b) F(at) ⟷ aF(aω)
(c) F(t/a) ⟷ aF(ω/a)
(d) F(at) ⟷ (1/a)F(ω/a)

Q7. A counter in which the output of one flip-flop acts as clock for other is termed
(a) decoder
(b) ripple counter
(c) ring counter
(d) synchronous counter

Q8. When cells are arranged in series then
(a) the EMF increase
(b) the EMF decreases
(c) the current capacity increases
(d) the current capacity decreases

Q9. Four voice signals each limited to 4 kHz and sampled at Nyquist rate, are converted into binary PCM signal using 256 quantization levels. The bit transmission rate for the time division multiplexing signal will be
(a) 8 kbps
(b) 64 kbps
(c) 256 kbps
(d) 5126 kbps

Q10. Which of the following waves do not exist in wave guides?
(a) TE waves
(b) TM waves
(c) TE and TM waves
(d) TEM waves

SOLUTIONS

S1. Ans.(a)
Sol. SCR remains ON even when gate current or trigger pulse is removed. It can be turned OFF by reversing the polarity of anode and cathode voltage.

S2. Ans.(c)
Sol. ASCII stands for “American Standard Code for Information Interchange”. It is a seven bit input output code. It is used for Bar Code reader, Serial Printer, Board Level Controller etc.

S3. Ans (d)
Sol. Given:
V_rms = 200 Volts
If the wave is triangular in shape, RMS voltage is –
V_rms = Vm√3
where,
V_m is peak value.
Now,
V_m = V_rms × √3
⇒ V_m = 200 × 1.73
So, V_m = 346
Hence, the peak voltage will be 346 volts.

S4. Ans.(c)
Sol. A Thermistor or Thermal resistor is defined as a type of resistor whose electrical resistance varies with changes in temperature.
There are two types of thermistors:
Negative Temperature Coefficient (NTC)
Positive Temperature Coefficient (PTC)

S5. Ans.(c)
Sol. Brewster’s angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. It is also known as the polarization angle.

S6. Ans.(d)
Sol. In Time Scaling property of Fourier Transform, we get
x(at) ↔┴( F.T ) 1/|a| X(ω/a)

S7. Ans.(b)
Sol.
A Ripple Counter is an asynchronous counter where only the first flip-flop is clocked by an external clock. All subsequent flip-flops are clocked by the output of the preceding flip-flop.
A Ring Counter is a synchronous counter in which all the flip-flops are clocked by an external clock i.e., all the FF are synchronized.
Decoder is a combinational circuit in which clock is not required. It has ‘n’ input lines and maximum of 2n output lines. Decoders are enabled by some code.

S8. Ans.(a)
Sol. When cells are arranged in series then EMF of the cells are added so, net EMF increases.

S9. Ans.(c)
Sol. Given:
No. of voice signals(N) = 4
fm = 4 kHz
No. of quantisation level = 256

We know that,
Bit Rate (Rb) = Nnfs
Quantisation level (L) = 2n
Now,
2n = 256
∴ n = 8 bits
and, fs = 2fm = 2x4kHz = 8 kHz
⇒ Rb = Nnfs = 4 x 8 x 8 kHz
= 256 kbps
Therefore, The bit transmission rate for the TDM signal will be 256 kbps.

S10. Ans.(d)
Sol. For TEM mode the current flow should be along the axis of the waveguide, which creates rotating magnetic fields which are normal to the electric fields generated due to the (moving) charges in the current carrying conductor. Since such a current source is absent and waveguide being a single conductor configuration, TEM mode cannot exist inside a waveguide. A pure TEM mode propagation is not possible in single conductor waveguide like as rectangular or cylindrical waveguide. Because TEM have
Ez = 0 and Hz = 0.
This makes Ex, Ey, Hx, Hy vanish. So, TEM wave can’t exist inside a waveguide.