Semiconductors & Communication · JEE Main previous year questions

2021 29 questions

1. Q412021 · 1 Sept 2021 · Shift 2

   A glass tumbler having inner depth of $17.5\mathrm{cm}$ is kept on a table. A student starts pouring water ($\mu =4/3$) into it while looking at the surface of water from the above. When he feels that the tumbler is half filled, he stops pouring water. Up to what height, the tumbler is actually filled?

   1. A.$11.7\mathrm{cm}$
   2. B.$10\mathrm{cm}$
   3. C.$7.5\mathrm{cm}$
   4. D.$8.75\mathrm{cm}$
   Show answer

   Answer: B

2. Q602021 · 1 Sept 2021 · Shift 2· Numerical answer

   A carrier wave with amplitude of 250 V is amplitude modulated by a sinusoidal base band signal of amplitude 150V. The ratio of minimum amplitude to maximum amplitude for the amplitude modulated wave is 50 : x, then value of x is ____________.

   Show answer

   Answer: 200

3. Q362021 · 26 Aug 2021 · Shift 2

   A light beam is described by $E=800\sin \omega \left(t-\frac{x}{c}\right)$. An electron is allowed to move normal to the propagation of light beam with a speed of $3\times 10^7{\text{ ms}}^{-1}$. What is the maximum magnetic force exerted on the electron?

   1. A.$1.28\times 10^{-18}\text{ N}$
   2. B.$1.28\times 10^{-21}\text{ N}$
   3. C.$12.8\times 10^{-17}\text{ N}$
   4. D.$12.8\times 10^{-18}\text{ N}$
   Show answer

   Answer: D

4. Q432021 · 26 Aug 2021 · Shift 2
   
   1. A.
   2. B.
   3. C.
   4. D.
   Show answer

   Answer: D

5. Q492021 · 26 Aug 2021 · Shift 2

   A transmitting antenna at top of a tower has a height of 50 m and the height of receiving antenna is 80 m. What is range of communication for Line of Sight (LoS) mode? [use radius of earth = 6400 km]

   1. A.45.5 km
   2. B.80.2 km
   3. C.144.1 km
   4. D.57.28 km
   Show answer

   Answer: D

6. Q582021 · 26 Aug 2021 · Shift 2· Numerical answer
   
   Show answer

   Answer: 120

7. Q592021 · 27 Jul 2021 · Shift 2· Numerical answer

   The water is filled upto height of 12 m in a tank having vertical sidewalls. A hole is made in one of the walls at a depth 'h' below the water level. The value of 'h' for which the emerging stream of water strikes the ground at the maximum range is ________ m.

   Show answer

   Answer: 6

8. Q602021 · 27 Jul 2021 · Shift 2· Numerical answer

   The maximum amplitude for an amplitude modulated wave is found to be 12V while the minimum amplitude is found to be 3V. The modulation index is 0.6x where x is ____________.

   Show answer

   Answer: 1

9. Q502021 · 25 Jul 2021 · Shift 1

   In amplitude modulation, the message signal $V_m(t)=10\sin (2\pi \times 10^{5}t)$ volts and Carrier signal $V_C(t)=20\sin (2\pi \times 10^{7}t)$ volts The modulated signal now contains the message signal with lower side band and upper side band frequency, therefore the bandwidth of modulated signal is $\alpha$ kHz. The value of $\alpha$ is :

   1. A.200 kHz
   2. B.50 kHz
   3. C.100 kHz
   4. D.0
   Show answer

   Answer: A

10. Q442021 · 25 Jul 2021 · Shift 2

    The instantaneous velocity of a particle moving in a straight line is given as $V=\alpha t+\beta t^2$, where $\alpha$ and $\beta$ are constants. The distance travelled by the particle between 1s and 2s is :

    1. A.$3\alpha +7\beta$
    2. B.$\frac{3}{2}\alpha +\frac{7}{3}\beta$
    3. C.$\frac{\alpha }{2}+\frac{\beta }{3}$
    4. D.$\frac{3}{2}\alpha +\frac{7}{2}\beta$
    Show answer

    Answer: B

11. Q582021 · 25 Jul 2021 · Shift 2· Numerical answer

    In a semiconductor, the number density of intrinsic charge carries at $27^{\circ }\mathrm{C}$ is $1.5\times 10^{16}/{\mathrm{m}}^3$. If the semiconductor is doped with impurity atom, the hole density increases to $4.5\times 10^{22}/{\mathrm{m}}^3$. The electron density in the doped semiconductor is ____ $\times 10^9/{\mathrm{m}}^3$.

    Show answer

    Answer: 5

12. Q592021 · 25 Jul 2021 · Shift 2· Numerical answer

    A message signal of frequency 20 kHz and peak voltage of 20 volt is used to modulate a carrier wave of frequency 1 MHz and peak voltage of 20 volt. The modulation index will be :

    Show answer

    Answer: 1

13. Q482021 · 22 Jul 2021 · Shift 2

    Consider a situation in which reverse biased current of a particular P-N junction increases when it is exposed to a light of wavelength $\le 621\text{ nm}$. During this process, enhancement in carrier concentration takes place due to generation of hole-electron pairs. The value of band gap is nearly.

    1. A.$1\text{ eV}$
    2. B.$4\text{ eV}$
    3. C.$0.5\text{ eV}$
    4. D.$2\text{ eV}$
    Show answer

    Answer: D

14. Q502021 · 22 Jul 2021 · Shift 2

    What should be the height of transmitting antenna and the population covered if the television telecast is to cover a radius of $150\text{ km}$? The average population density around the tower is $2000/{\text{km}}^2$ and the value of $R_e=6.5\times 10^6\text{ m}$.

    1. A.$\text{Height}=1241\text{ m},\text{ Population covered}=7\times 10^5$
    2. B.$\text{Height}=1731\text{ m},\text{ Population covered}=1413\times 10^5$
    3. C.$\text{Height}=1800\text{ m},\text{ Population covered}=1413\times 10^8$
    4. D.$\text{Height}=1600\text{ m},\text{ Population covered}=2\times 10^5$
    Show answer

    Answer: B

15. Q532021 · 22 Jul 2021 · Shift 2· Numerical answer

    Three particles P, Q and R are moving along the vectors $\vec{A}=\hat{i}+\hat{j}$, $\vec{B}=\hat{j}+\hat{k}$ and $\vec{C}=-\hat{i}+\hat{j}$ respectively. They strike on a point and start to move in different directions. Now particle P is moving normal to the plane which contains vector $\vec{A}$ and $\vec{B}$. Similarly particle Q is moving normal to the plane which contains vector $\vec{A}$ and $\vec{C}$. The angle between the direction of motion of P and Q is ${\cos }^{-1}\left(\frac{1}{\sqrt{x}}\right)$. Then the value of x is ________.

    Show answer

    Answer: 3

16. Q342021 · 20 Jul 2021 · Shift 1

    The normal reaction 'N' for a vehicle of $800\text{ kg}$ mass, negotiating a turn on a $30^{\circ }$ banked road at maximum possible speed without skidding is ________ $\times 10^3{\text{ kg m/s}}^2$. [Given $\cos 30^{\circ }=0.87,{\mu }_s=0.2$]

    1. A.$12.4$
    2. B.$7.2$
    3. C.$6.96$
    4. D.$10.2$
    Show answer

    Answer: D

17. Q592021 · 20 Jul 2021 · Shift 1· Numerical answer

    A carrier wave $V_c(t)=160\sin (2\pi \times 10^{6}t)\text{ volts}$ is made to vary between $V_{\max }=200\text{ V}$ and $V_{\min }=120\text{ V}$ by a message signal $V_m(t)=A_m\sin (2\pi \times 10^{3}t)\text{ volts}$. The peak voltage $A_m$ of the modulating signal is ________.

    Show answer

    Answer: 40

18. Q482021 · 18 Mar 2021 · Shift 2

    The correct relation between $\alpha$ (ratio of collector current to emitter current) and $\beta$ (ratio of collector current to base current) of a transistor is :

    1. A.$\beta =\frac{\alpha }{1+\alpha }$
    2. B.$\alpha =\frac{\beta }{1-\alpha }$
    3. C.$\alpha =\frac{\beta }{1+\beta }$
    4. D.$\beta =\frac{1}{1-\alpha }$
    Show answer

    Answer: C

19. Q592021 · 18 Mar 2021 · Shift 2· Numerical answer

    A TV transmission tower antenna is at a height of 20 m. Suppose that the receiving antenna is at : (i) ground level (ii) a height of 5 m. The increase in antenna range in case (ii) relative to case (i) is n%. The value of n, to the nearest integer, is ___________.

    Show answer

    Answer: 50

20. Q602021 · 18 Mar 2021 · Shift 2· Numerical answer
    
    Show answer

    Answer: 200

21. Q342021 · 16 Mar 2021 · Shift 1

    A block of 200 g mass moves with a uniform speed in a horizontal circular groove, with vertical side walls of radius 20 cm. If the block takes 40 s to complete one round, the normal force by the side walls of the groove is :

    1. A.$9.859\times 10^{-2}\mathrm{N}$
    2. B.$0.0314\mathrm{N}$
    3. C.$9.859\times 10^{-4}\mathrm{N}$
    4. D.$6.28\times 10^{-3}\mathrm{N}$
    Show answer

    Answer: C

22. Q492021 · 16 Mar 2021 · Shift 1

    A 25 m long antenna is mounted on an antenna tower. The height of the antenna tower is 75 m. The wavelength (in meter) of the signal transmitted by this antenna would be :

    1. A.200
    2. B.400
    3. C.100
    4. D.300
    Show answer

    Answer: C

23. Q512021 · 16 Mar 2021 · Shift 1· Numerical answer
    
    Show answer

    Answer: 5

24. Q352021 · 26 Feb 2021 · Shift 1

    LED is constructed from Ga-As-P semiconducting material. The energy gap of this LED is 1.9 eV. Calculate the wavelength of light emitted and its colour. $[h=6.63\times 10^{-34}\mathrm{Js}\text{ and }c=3\times 10^8\mathrm{m}{\mathrm{s}}^{-1}]$

    1. A.654 nm and orange colour
    2. B.654 nm and red colour
    3. C.1046 nm and red colour
    4. D.1046 nm and blue colour
    Show answer

    Answer: B

25. Q602021 · 26 Feb 2021 · Shift 1· Numerical answer

    The maximum and minimum amplitude of an amplitude modulated wave is 16V and 8V respectively. The modulation index for this amplitude modulated wave is $x\times 10^{-2}$. The value of x is _________.

    Show answer

    Answer: 33