Propagation of Waves

Q.

Two identical antennas mounted on identical towers are separated from each other by a distance of $45Km$. What should nearly be the minimum height of the receiving antenna to receive the signals in line of sight? (Assume the radius of the earth is $6400Km$).

1. $19.77m$

2. $79.1m$

3. $158.2m$

4. $39.55m$

Q.

In an optical fiber, the inner core is ------------------ than the cladding

1. Less Dense

2. Same density

3. Denser

4. None of the option

Q.

What is first Fresnel Zone?

Q.

When electromagnetic waves are allowed to pass through a glass slab, then

1. velocity of the waves remains constant but frequency changes

2. frequency and wavelength of waves remain constant but its velocity changes

3. frequency of the waves remains constant but wavelength changes

4. velocity remains constant but wavelength changes

Q. Mean optical power launched into an 8 km fiber is 120 $\mu$W and mean output power is 4 $\mu$W, then the overall attenuation is (Given log 30 = 1.477)

1. 14.77 dB
2. 16.77 dB
3. 3.01 dB
4. None of these

Q. The waves used in telecommunication are?

1. IR
2. UV
3. Microwave
4. Cosmic rays

Q.

Which of the following is related to telecommunication?

1. X-rays

2. r-rays

3. Sound wave

4. Microwaves

Q. In a radio receiver, the short wave and medium wave stations are tuned by using the same capacitor but coils of different inductance $L_s$ and $L_m$ respectively then

1. $L_s>L_m$
   
2. $L_s<L_m$
3. $L_s=L_m$
4. None of these

Q. The electromagnetic waves of frequency 2 MHz to 30 MHz are

1. In ground wave propagation
2. In sky wave propagation
3. In microwave propagation
4. In satellite communication

Q. A ground receiver station is receiving a signal at (i) 5 MHz and transmitted from a ground transmitter at a height of 300 m, located at a distance of 100 km from the receiver station. The signal is coming via__________. Radius of earth = 6.4 $\times {10}^6$m. $N_{max}$ of isosphere = ${10}^{12}{m}^3$

1. Space wave
2. Sky wave propagation
3. Satellite transponder
4. All of these

Q. A photodetector is made from a semiconductor In ${}_{0.53}Ga$${}_{0.47}As$ with $E_g$ = 0.73 eV. What is the maximum wavelength, which it can detect

1. 1000 nm
2. 1703 nm
3. 500 nm
4. 173 nm

Q. A laser beam of pulse power ${10}^{12}$ watt is focussed on an object are ${10}^{-4}{cm}^2$ . The energy flux in watt/ ${cm}^2$ at the point of focus is

1. ${10}^{20}$
2. ${10}^{16}$
3. ${10}^8$
4. ${10}^4$

Q. A laser beam of pulse power ${10}^{12}$ watt is focussed on an object are ${10}^{-4}{cm}^2$ . The energy flux in watt/ ${cm}^2$ at the point of focus is

1. ${10}^{20}$
2. ${10}^{16}$
3. ${10}^8$
4. ${10}^4$

Q. In short wave communication waves of which of the following frequencies will be reflected back by the ionospheric layer, having electron density ${10}^{11}$ per $m^3$

1. 2 MHz
2. 10 MHz
3. 12 MHz
4. 18 MHz

Q. A ground receiver station is receiving a signal at (i) 5 MHz and transmitted from a ground transmitter at a height of 300 m, located at a distance of 100 km from the receiver station. The signal is coming via__________. Radius of earth = 6.4 $\times {10}^6$m. $N_{max}$ of isosphere = ${10}^{12}{m}^3$

1. Space wave
2. Sky wave propagation
3. Satellite transponder
4. All of these

Q. Television broadcast use wave mode of propagation.

1. sky
2. space
3. surface

Q. The T.V. transmission tower in Delhi has a height of $240\text{m}$. The distance up to which that the broadcast can be received, (taking the radius of earth to be $6.4\times {10}^6\text{m}$) is :-

1. $100\text{km}$
2. $60\text{km}$
3. $55\text{km}$
4. $50\text{km}$

Q. If a, b, c, d are inputs to a gate and x is tis output then, as per the following time graph, the gate is:

1. AND
2. OR
3. NAND
4. NOT

Q. The efficiency of radiated signals depends on the size of antenna.

1. False
2. True

Q. A sky wave with a frequency 55 MHz is incident on D-region of earth's atmosphere at ${45}^{\circ }$. The angle of refraction is (electron density for D-region is 400 electron/${cm}^3$)

1. ${60}^{\circ }$
2. ${45}^{\circ }$
3. ${30}^{\circ }$
4. ${15}^{\circ }$

Q. Read the assertion and reason carefully to mark the correct option out of the options given below:
Assertion : The electrical conductivity of earth's atmosphere decreases with altitude.
Reason : The high energy particles (i.e. g-rays and cosmic rays) coming from outer space and entering our earth's atmosphere cause ionisation of the atoms of the gases present there and the pressure of gases decreases with increase in altitude.
(a)If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b)If both assertion and reason are true but reason is not the correct explanation of the assertion.
(c)If assertion is true but reason is false.
(d)If the assertion and reason both are false.
(e)If assertion is false but reason is true.

1. a
2. b
3. c
4. d
5. e

Q. For sky wave propagation of a 10 MHz signal, what should be the minimum electron density in ionosphere

1. ~ 1.2 $\times$ ${10}^{12}{m}^{-3}$
2. ~ ${10}^6{m}^{-3}$
3. ~ ${10}^{14}{m}^{-3}$
4. ~ ${10}^{22}{m}^{-3}$

Q. The attenuation of surface waves with increase in frequency.

1. increases
2. decreases
3. remains zero