Semiconductors & Communication · JEE Main previous year questions

A radio can tune to any station in $6\mathrm{MHz}$ to $10\mathrm{MHz}$ band. The value of corresponding wavelength bandwidth will be :

1. A.$4\mathrm{m}$
2. B.$20\mathrm{m}$
3. C.$30\mathrm{m}$
4. D.$50\mathrm{m}$

In AM modulation, a signal is modulated on a carrier wave such that maximum and minimum amplitudes are found to be 6 V and 2 V respectively. The modulation index is :

1. A.100%
2. B.80%
3. C.60%
4. D.50%

A speech signal given by $11\sin (2200\pi t)\text{ V}$ is used for amplitude modulation with a carrier signal given by $44\sin (6600\pi t)\text{ V}$. The minimum amplitude of modulated wave will be :

1. A.$33\text{ V}$
2. B.$55\text{ V}$
3. C.$8.25\text{ V}$
4. D.$13.75\text{ V}$

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

Amplitude modulated wave is represented by $V_{AM}=10[1+0.4\cos (2\pi \times 10^{4}t)]\cos (2\pi \times 10^{7}t)$. The total bandwidth of the amplitude modulated wave is :

1. A.$10\mathrm{kHz}$
2. B.$20\mathrm{MHz}$
3. C.$20\mathrm{kHz}$
4. D.$10\mathrm{MHz}$

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

The height of a transmitting antenna at the top of a tower is $25\mathrm{m}$ and that of receiving antenna is, $49\mathrm{m}$. The maximum distance between them, for satisfactory communication in LOS (Line-Of-Sight) is $K\sqrt{5}\times 10^2\mathrm{m}$. The value of $K$ is ____. (Assume radius of Earth is $64\times 10^{+5}\mathrm{m}$) [Calculate upto nearest integer value]

For a transistor to act as a switch, it must be operated in

1. A.Active region.
2. B.Saturation state only.
3. C.Cut-off state only.
4. D.Saturation and cut-off state.

We do not transmit low frequency signal to long distances because- (a) The size of the antenna should be comparable to signal wavelength which is unreal solution for a signal of longer wavelength. (b) Effective power radiated by a long wavelength baseband signal would be high. (c) We want to avoid mixing up signals transmitted by different transmitter simultaneously. (d) Low frequency signal can be sent to long distances by superimposing with a high frequency wave as well. Therefore, the most suitable option will be :

1. A.All statements are true
2. B.(a), (b) and (c) are true only
3. C.(a), (c) and (d) are true only
4. D.(b), (c) and (d) are true only

1. A.1 : 2
2. B.5 : 1
3. C.1 : 40
4. D.20 : 1

Choose the correct statement for amplitude modulation :

1. A.Amplitude of modulating signal is varied in accordance with the information signal.
2. B.Amplitude of modulated signal is varied in accordance with the information signal.
3. C.Amplitude of carrier signal is varied in accordance with the information signal.
4. D.Amplitude of modulated signal is varied in accordance with the modulating signal.

Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R. Assertion A : If we move from poles to equator, the direction of acceleration due to gravity of earth always points towards the center of earth without any variation in its magnitude. Reason R : At equator, the direction of acceleration due to the gravity is towards the center of earth. In the light of 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.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.

The photodiode is used to detect the optical signals. These diodes are preferably operated in reverse biased mode because :

1. A.fractional change in majority carriers produce higher forward bias current
2. B.fractional change in majority carriers produce higher reverse bias current
3. C.fractional change in minority carriers produce higher forward bias current
4. D.fractional change in minority carriers produce higher reverse bias current

Match List I with List II $$\begin{array}{llll}& \text{List - I}& & \text{List -II}\\ \text{A.}& \text{Facsimile}& \text{I.}& \text{Static Document Image}\\ \text{B.}& \text{Guided media Channel}& \text{II.}& \text{Local Broadcast Radio}\\ \text{C.}& \text{Frequency Modulation}& \text{III.}& \text{Rectangular wave}\\ \text{D.}& \text{Digital Signal}& \text{IV.}& \text{Optical Fiber}\end{array}$$ Choose the correct answer from the following options:

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

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.$8.75\mathrm{cm}$

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 ____________.

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.$12.8\times 10^{-18}\text{ N}$

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

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

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.

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 ____________.