Semiconductors & Communication · JEE Main previous year questions

If the height of transmitting and receiving antennas are 80 m each, the maximum line of sight distance will be: Given : Earth's radius $=6.4\times 10^6$ m

1. A.28 km
2. B.64 km
3. C.32 km
4. D.36 km

1. A.
2. B.
3. C.
4. D.

The modulation index for an A.M. wave having maximum and minimum peak-to-peak voltages of 14 mV and 6 mV respectively is-

1. A.0.4
2. B.0.6
3. C.1.4
4. D.0.2

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R Assertion A : Photodiodes are used in forward bias usually for measuring the light intensity. Reason R : For a p-n junction diode, at applied voltage V the current in the forward bias is more than the current in the reverse bias for $|{\mathrm{V}}_{\mathrm{z}}|>\pm \mathrm{V}\ge |{\mathrm{V}}_0|$ where ${\mathrm{V}}_0$ is the threshold voltage and ${\mathrm{V}}_{\mathrm{z}}$ is the breakdown voltage. In the light of the above statements, choose the correct answer from the options given below

1. A.Both A and R are true but R is NOT the correct explanation of A
2. B.A is true but R is false
3. C.Both A and R are true and R is the correct explanation of A
4. D.A is false but R is true

A message signal of frequency 5 kHz is used to modulate a carrier signal of frequency 2 MHz. The bandwidth for amplitude modulation is :

1. A.10 kHz
2. B.2.5 kHz
3. C.20 kHz
4. D.5 kHz

A bowl filled with very hot soup cools from $98^{\circ }\mathrm{C}$ to $86^{\circ }\mathrm{C}$ in 2 minutes when the room temperature is $22^{\circ }\mathrm{C}$. How long it will take to cool from $75^{\circ }\mathrm{C}$ to $69^{\circ }\mathrm{C}$?

1. A.2 minutes
2. B.0.5 minute
3. C.1.4 minutes
4. D.1 minute

The distance travelled by a particle is related to time t as $x=4{\mathrm{t}}^2$. The velocity of the particle at t=5s is :-

1. A.$25\mathrm{m}{\mathrm{s}}^{-1}$
2. B.$20\mathrm{m}{\mathrm{s}}^{-1}$
3. C.$8\mathrm{m}{\mathrm{s}}^{-1}$
4. D.$40\mathrm{m}{\mathrm{s}}^{-1}$

Statement I : When a Si sample is doped with Boron, it becomes P type and when doped by Arsenic it becomes N-type semi conductor such that P-type has excess holes and N-type has excess electrons. Statement II : When such P-type and N-type semi-conductors, are fused to make a junction, a current will automatically flow which can be detected with an externally connected ammeter. In the light of above statements, choose the most appropriate answer from the options given below

1. A.Statement I is incorrect but statement II is correct
2. B.Both Statement I and statement II are correct
3. C.Statement I is correct but statement II is incorrect
4. D.Both Statement I and Statement II are incorrect

A spherical drop of liquid splits into 1000 identical spherical drops. If ${\mathrm{u}}_{\mathrm{i}}$ is the surface energy of the original drop and ${\mathrm{u}}_{\mathrm{f}}$ is the total surface energy of the resulting drops, then (ignoring evaporation), $\frac{u_f}{u_i}=\left(\frac{10}{x}\right)$. Then value of x is ____ :

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R Assertion A : Photodiodes are preferably operated in reverse bias condition for light intensity measurement. Reason R : The current in the forward bias is more than the current in the reverse bias for a $p-n$ junction diode. In the light of the above statements, choose the correct answer from the options given below :

1. A.Both A and R are true and R is the correct explanation of A
2. B.A is false but R is true
3. C.A is true but R is false
4. D.Both A and R are true but R is NOT the correct explanation of A

Two long straight wires P and Q carrying equal current 10A each were kept parallel to each other at $5\mathrm{cm}$ distance. Magnitude of magnetic force experienced by $10\mathrm{cm}$ length of wire P is ${\mathrm{F}}_1$. If distance between wires is halved and currents on them are doubled, force ${\mathrm{F}}_2$ on $10\mathrm{cm}$ length of wire P will be:

1. A.$\frac{{\mathrm{F}}_1}{8}$
2. B.$10{\mathrm{F}}_1$
3. C.$\frac{{\mathrm{F}}_1}{10}$
4. D.$8{\mathrm{F}}_1$

1. A.$\frac{1}{3}$
2. B.$1$
3. C.$\frac{1}{4}$
4. D.$\frac{1}{2}$

1. A.NOR
2. B.OR
3. C.NAND
4. D.AND

Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Clothes containing oil or grease stains cannot be cleaned by water wash. Reason (R): Because the angle of contact between the oil/grease and water is obtuse. In the light of the above statements, choose the correct answer from the option given below.

1. A.Both (A) and (R) are true and (R) is the correct explanation of (A)
2. B.Both (A) and (R) are true but (R) is not the correct explanation of (A)
3. C.(A) is true but (R) is false
4. D.(A) is false but (R) is true

Find the modulation index of an AM wave having $8\mathrm{V}$ variation where maximum amplitude of the AM wave is $9\mathrm{V}$.

1. A.0.8
2. B.0.5
3. C.0.2
4. D.0.1

A modulating signal $2\sin (6.28\times 10^6)t$ is added to the carrier signal $4\sin (12.56\times 10^9)t$ for amplitude modulation. The combined signal is passed through a non-linear square law device. The output is then passed through a band pass filter. The bandwidth of the output signal of band pass filter will be ____ $\mathrm{MHz}$.

1. A.
2. B.
3. C.
4. D.

In the case of amplitude modulation to avoid distortion the modulation index ($\mu$) should be :

1. A.$\mu \le 1$
2. B.$\mu \ge 1$
3. C.$\mu =2$
4. D.$\mu =0$

1. A.$0.1\text{ V}$
2. B.$1.0\text{ V}$
3. C.$10\text{ V}$
4. D.$100\text{ V}$

A FM Broadcast transmitter, using modulating signal of frequency 20 kHz has a deviation ratio of 10. The Bandwidth required for transmission is :

1. A.220 kHz
2. B.180 kHz
3. C.360 kHz
4. D.440 khz

1. A.AND gate
2. B.OR gate
3. C.NOR gate
4. D.NAND gate

With reference to the observations in photo-electric effect, identify the correct statements from below : (A) The square of maximum velocity of photoelectrons varies linearly with frequency of incident light. (B) The value of saturation current increases on moving the source of light away from the metal surface. (C) The maximum kinetic energy of photo-electrons decreases on decreasing the power of LED (light emitting diode) source of light. (D) The immediate emission of photo-electrons out of metal surface can not be explained by particle nature of light/electromagnetic waves. (E) Existence of threshold wavelength can not be explained by wave nature of light/ electromagnetic waves. Choose the correct answer from the options given below :

1. A.(A) and (B) only
2. B.(A) and (E) only
3. C.(C) and (E) only
4. D.(D) and (E) only

For a constant collector-emitter voltage of $8\mathrm{V}$, the collector current of a transistor reached to the value of $6\mathrm{mA}$ from $4\mathrm{mA}$, whereas base current changed from $20\mu \mathrm{A}$ to $25\mu \mathrm{A}$ value. If transistor is in active state, small signal current gain (current amplification factor) will be :

1. A.240
2. B.400
3. C.0.0025
4. D.200

1. A.0.2
2. B.0.1
3. C.0.3
4. D.0.4