Semiconductors & Communication · JEE Main previous year questions

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : The property of body, by virtue of which it tends to regain its original shape when the external force is removed, is Elasticity. Reason (R) : The restoring force depends upon the bonded inter atomic and inter molecular force of solid. In the light of the above statements, choose the correct answer from the options given below :

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

The distance travelled by an object in time $t$ is given by $s=(2.5)t^2$. The instantaneous speed of the object at $t=5\text{ s}$ will be:

1. A.$5{\text{ ms}}^{-1}$
2. B.$12.5{\text{ ms}}^{-1}$
3. C.$62.5{\text{ ms}}^{-1}$
4. D.$25{\text{ ms}}^{-1}$

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

To radiate EM signal of wavelength $\lambda$ with high efficiency, the antennas should have a minimum size equal to:

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

In an n-p-n common emitter (CE) transistor the collector current changes from $5\text{ mA}$ to $16\text{ mA}$ for the change in base current from $100\mu \text{A}$ and $200\mu \text{A}$, respectively. The current gain of transistor is _________.

1. A.$210$
2. B.$0.9$
3. C.$9$
4. D.$110$

A transmitting antenna is kept on the surface of the earth. The minimum height of receiving antenna required to receive the signal in line of sight at $4\text{ km}$ distance from it is $x\times 10^{-2}\text{ m}$. The value of $x$ is _________. (Let, radius of earth $\mathrm{R}=6400\text{ km}$)

1. A.$1.25$
2. B.$125$
3. C.$1250$
4. D.$12.5$

1. A.$13\Omega$
2. B.$13.3\Omega$
3. C.$10\Omega$
4. D.$12\Omega$

A carrier wave of amplitude 15 V is modulated by a sinusoidal base band signal of magnitude 3 V. The ratio of maximum amplitude to minimum amplitude in an amplitude modulated wave is

1. A.1
2. B.5
3. C.2
4. D.$\frac{3}{2}$

A message signal of frequency $3\text{ kHz}$ is used to modulate a carrier signal of frequency $1.5\text{ MHz}$. The bandwidth of the amplitude modulated wave is

1. A.6 MHz
2. B.6 kHz
3. C.3 MHz
4. D.3 kHz

A TV transmitting antenna is $98\text{ m}$ high and the receiving antenna is at the ground level. If the radius of the earth is $6400\text{ km}$, the surface area covered by the transmitting antenna is approximately:

1. A.$4868{\text{ km}}^2$
2. B.$1240{\text{ km}}^2$
3. C.$3942{\text{ km}}^2$
4. D.$1549{\text{ km}}^2$

Given below are two statements Statement I : Area under velocity- time graph gives the distance travelled by the body in a given time. Statement II : Area under acceleration- time graph is equal to the change in velocity in the given time. In the light of given statements, choose the correct answer from the options given below.

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

Given below are two statements: one is labelled as Assertion $\mathbf{A}$ and the other is labelled as Reason $\mathbf{R}$ Assertion A : Electromagnets are made of soft iron. Reason R : Soft iron has high permeability and low retentivity. In the light of above, statements, choose the most appropriate answer from the options given below.

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

1. A.${\mathrm{I}}_{\mathrm{b}}=100\mu \mathrm{A}$
2. B.${\mathrm{I}}_{\mathrm{b}}=0.1\mu \mathrm{A}$
3. C.${\mathrm{I}}_{\mathrm{b}}=1.0\mu \mathrm{A}$
4. D.${\mathrm{I}}_{\mathrm{b}}=10\mu \mathrm{A}$

The power radiated from a linear antenna of length $l$ is proportional to (Given, $\lambda =$ Wavelength of wave):

1. A.${\left(\frac{l}{\lambda }\right)}^2$
2. B.$\frac{l}{{\lambda }^2}$
3. C.$\frac{l^2}{\lambda }$
4. D.$\frac{l}{\lambda }$

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

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R Assertion A : When a body is projected at an angle $45^{\circ }$, it's range is maximum. Reason R : For maximum range, the value of $\sin 2\theta$ should be equal to one. In the light of the above statements, choose the correct answer from the options given below:

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

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

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R Assertion A: Diffusion current in a p-n junction is greater than the drift current in magnitude if the junction is forward biased. Reason R: Diffusion current in a p-n junction is from the n-side to the p-side if the junction is forward biased. In the light of the above statements, choose the most appropriate answer from the options given below

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

For an amplitude modulated wave the minimum amplitude is $3\text{ V}$, while the modulation index is $60\%$. The maximum amplitude of the modulated wave is:

1. A.$5\text{ V}$
2. B.$12\text{ V}$
3. C.$10\text{ V}$
4. D.$15\text{ V}$

Match List I with List II: | List I | List II | | :--- | :--- | | A. Intrinsic semiconductor | I. Fermi-level near the valence band | | B. n-type semiconductor | II. Fermi-level in the middle of valence and conduction band. | | C. p-type semiconductor | III. Fermi-level near the conduction band | | D. Metals | IV. Fermi-level inside the conduction band | Choose the correct answer from the options given below :

1. A.A-III, B-I, C-II, D-IV
2. B.A-II, B-I, C-III, D-IV
3. C.A-I, B-II, C-III, D-IV
4. D.A-II, B-III, C-I, D-IV

1. A.$800\text{ N}$
2. B.$600\text{ N}$
3. C.$200\sqrt{3}\text{ N}$
4. D.$800\sqrt{2}\text{ N}$

Given below are two statements : Statement I: In a typical transistor, all three regions emitter, base and collector have same doping level. Statement II: In a transistor, collector is the thickest and base is the thinnest segment. In the light of the above statements, choose the most appropriate answer from the options given below.

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

A horse rider covers half the distance with $5\text{ m/s}$ speed. The remaining part of the distance was travelled with speed $10\text{ m/s}$ for half the time and with speed $15\text{ m/s}$ for other half of the time. The mean speed of the rider averaged over the whole time of motion is $\frac{x}{7}\text{ m/s}$. The value of $x$ is ___________.

Which one of the following statement is not correct in the case of light emitting diodes? A. It is a heavily doped p-n junction. B. It emits light only when it is forward biased. C. It emits light only when it is reverse biased. D. The energy of the light emitted is equal to or slightly less than the energy gap of the semiconductor used. Choose the correct answer from the options given below:

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