Semiconductors & Communication · JEE Main previous year questions

2019 13 questions

1. Q542019 · 12 Apr 2019 · Shift 2
   
   1. A.3.5 mA
   2. B.1.5 mA
   3. C.2.5 mA
   4. D.7.5 mA
   Show answer

   Answer: A

2. Q582019 · 12 Apr 2019 · Shift 2

   In an amplitude modulator circuit, the carrier wave is given by, $\text{C}(t)=4\sin (20000\pi t)$ while modulating signal is given by, $\text{m}(t)=2\sin (2000\pi t)$. The values of modulation index and lower side band frequency are :

   1. A.0.3 and 9 kHz
   2. B.0.5 and 10 kHz
   3. C.0.4 and 10 kHz
   4. D.0.5 and 9 kHz
   Show answer

   Answer: D

3. Q552019 · 10 Apr 2019 · Shift 1

   A message signal of frequency 100 MHz and peak voltage 100 V is used to execute amplitude modulation on a carrier wave of frequency 300 GHz and peak voltage 400 V. The modulation index and difference between the two side band frequencies are :

   1. A.0.25; $1\times 10^8\mathrm{Hz}$
   2. B.4; $2\times 10^8\mathrm{Hz}$
   3. C.4; $1\times 10^8\mathrm{Hz}$
   4. D.0.25; $2\times 10^8\mathrm{Hz}$
   Show answer

   Answer: D

4. Q592019 · 10 Apr 2019 · Shift 1

   An n-p-n transistor operates as a common emitter amplifier, with a power gain of 60 dB. The input circuit resistance is $100\Omega$ and the output load resistance is $10\mathrm{k\Omega }$. The common emitter current gain $\beta$ is :

   1. A.$10^4$
   2. B.$10^2$
   3. C.$6\times 10^2$
   4. D.60
   Show answer

   Answer: B

5. Q592019 · 9 Apr 2019 · Shift 1

   An NPN transistor is used in common emitter configuration as an amplifier with $1\mathrm{k\Omega }$ load resistance. Signal voltage of 10 mV is applied across the base-emitter. This produces a 3 mA change in the collector current and $15\mu \mathrm{A}$ change in the base current of the amplifier. The input resistance and voltage gain are :

   1. A.$0.67\mathrm{k\Omega }$, 200
   2. B.$0.33\mathrm{k\Omega }$, 1.5
   3. C.$0.67\mathrm{k\Omega }$, 300
   4. D.$0.33\mathrm{k\Omega }$, 300
   Show answer

   Answer: C

6. Q602019 · 9 Apr 2019 · Shift 1

   A signal $A\cos \omega t$ is transmitted using $v_0\sin {\omega }_{0}t$ as carrier wave. The correct amplitude modulated (AM) signal is

   1. A.$v_0\sin {\omega }_{0}t+A\cos \omega t$
   2. B.$(v_0+A)\cos \omega t\sin {\omega }_{0}t$
   3. C.$v_0\sin [{\omega }_0(1+0.01A\sin \omega t)t]$
   4. D.$v_0\sin {\omega }_{0}t+\frac{A}{2}\sin ({\omega }_0-\omega )t+\frac{A}{2}\sin ({\omega }_0+\omega )t$
   Show answer

   Answer: D

7. Q432019 · 9 Apr 2019 · Shift 2
   
   1. A.NAND
   2. B.AND
   3. C.NOR
   4. D.OR
   Show answer

   Answer: D

8. Q592019 · 9 Apr 2019 · Shift 2

   The physical sizes of the transmitter and receiver antenna in a communication system are :-

   1. A.proportional to carrier frequency
   2. B.inversely proportional to carrier frequency
   3. C.inversely proportional to modulation frequency
   4. D.independent of both carrier and modulation frequency
   Show answer

   Answer: B

9. Q562019 · 8 Apr 2019 · Shift 2

   A common emitter amplifier circuit, built using an npn transistor, is shown in the figure. Its dc current gain is 250, $R_C=1\mathrm{k\Omega }$ and $V_{CC}=10\mathrm{V}$. What is the minimum base current for $V_{CE}$ to reach saturation ?

   1. A.$100\mu \mathrm{A}$
   2. B.$7\mu \mathrm{A}$
   3. C.$10\mu \mathrm{A}$
   4. D.$40\mu \mathrm{A}$
   Show answer

   Answer: D

10. Q582019 · 8 Apr 2019 · Shift 2

    In a line of sight radio communication, a distance of about 50 km is kept between the transmitting and receiving antennas. If the height of the receiving antenna is 70m, then the minimum height of the transmitting antenna should be : (Radius of the Earth = $6.4\times 10^6\mathrm{m}$).

    1. A.40 m
    2. B.20 m
    3. C.51 m
    4. D.32 m
    Show answer

    Answer: D

11. Q602019 · 12 Jan 2019 · Shift 1

    A 100 V carrier wave is made to vary between 160 V and 40 V by a modulating signal. What is the modulation index ?

    1. A.0.5
    2. B.0.6
    3. C.0.4
    4. D.0.3
    Show answer

    Answer: B

12. Q582019 · 12 Jan 2019 · Shift 2
    
    1. A.$20\mu \mathrm{A}$ and 2.8 V
    2. B.$25\mu \mathrm{A}$ and 2.8 V
    3. C.$20\mu \mathrm{A}$ and 3.5 V
    4. D.$25\mu \mathrm{A}$ and 3.5 V
    Show answer

    Answer: D

13. Q572019 · 9 Jan 2019 · Shift 1

    Mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an n-type semiconductor, the density of electrons is $10^{19}{\text{ m}}^{-3}$ and their mobility is $1.6{\text{ m}}^2/(\text{V.s})$ then the resistivity of the semiconductor (since it is an n-type semiconductor contribution of holes is ignored) is close to :

    1. A.$2\Omega \text{m}$
    2. B.$4\Omega \text{m}$
    3. C.$0.4\Omega \text{m}$
    4. D.$0.2\Omega \text{m}$
    Show answer

    Answer: C