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प्रश्न
Write a short note on surface wave propagation of electromagnetic waves.
उत्तर
Definition :
When the electromagnetic waves (radiowaves) from the transmitting antenna propagate along the surface of
the earth so as to reach the receiving antenna, the wave propagation is called ground wave propagation
(surface wave propagation). [1 mark]
Explanation :
(i) Ground waves are the radiowaves which propagate along the surface of the earth.
(ii) There is loss of power in a signal during its propagation on the surface of the earth due to partial
absorption of energy by ground. Hence ground wave propagation is suitable for low frequency and
medium frequency. It is used for local broadcasting.
(iii) Ground wave propagation is possible only when the transmitting and receiving antenna are close to
the earth’s surface.
APPEARS IN
संबंधित प्रश्न
(i) Which mode of propagation is used by shortwave broadcast services having frequency range from a few MHz upto 30 MHz? Explain diagrammatically how long distance communication can be achieved by this mode.
(ii) Why is there an upper limit to frequency of waves used in this mode?
What is space wave propagation?
The outermost layer of the earth’s atmosphere is _______.
(A) stratosphere
(B) mesospher
(C) troposphere
(D) ionosphere
In which directions do the electric and magnetic field vectors oscillate in an electromagnetic wave propagating along the x-axis?
Explain why ground wave communication mode cannot be used for long-distance communication using high frequencies
The reflected waves from an ionosphere are _____.
(a) ground waves
(b) sky waves
(c) space waves
(d) very high-frequency waves
Explain why this mode cannot be used for long distance communication using high frequencies.
Describe briefly, by drawing suitable diagram, the space wave modes of propagation. Mention the frequency range of the waves in these modes of propagation ?
Name the three different modes of propagation of electromagnetic waves. Explain, using a proper diagram the mode of propagation used in the frequency range from a few MHz to 40 MHz.
Explain with the help of a diagram how long distance communication can be achieved by ionospheric reflection of radio waves.
What is ground wave communication? On what factors does the maximum range of propagation in this mode depend?
Propagation of Electromagnetic Wave?
In sky wave mode of propagation, why is the frequency range of transmitting signals restricted to less than 30 MHz?
Depict the fields diagram of an electromagnetic wave propagating along positive X-axis with its electric field along the Y-axis.
Light from a sodium lamp (S) passes through two polaroid sheets P1 and P2 as shown in fig. What will be the effect on the intensity of the light transmitted (i) by P1 and (ii) by P2 on the rotating polaroid P1 about the direction of propagation of light? Justify your answer in both cases.
The frequency range of 3 MHz to 30 MHz is used for ____________.
The radio wave of frequency 300 MHz to 3000 MHz be.long to
In which frequencies range space waves are normally propagate:-
Propagation constant of a transmission line is
The characteristic impedance of a coaxial cable is of the order of
A TV transmission tower has a height of 240 m. Signals broadcast from this tower will be received by LOS communication at a distance of (assume the radius of earth to be 6.4 × 106 m)
- 100 km
- 24 km
- 55 km
- 50 km
The maximum frequency for reflection of sky waves from a certain layer of the ionosphere is found to be fmax = 9(Nmax)1/2, where Nmax is the maximum electron density at that layer of the ionosphere. On a certain day, it is observed that signals of frequencies higher than 5 MHz are not received by reflection from the F1 layer of the ionosphere while signals of frequencies higher than 8 MHz are not received by reflection from the F2 layer of the ionosphere. Estimate the maximum electron densities of the F1 and F2 layers on that day.
(i) The intensity of a light pulse travelling along a communication channel decreases exponentially with distance x according to the relation I = Ioe–αx, where Io is the intensity at x = 0 and α is the attenuation constant. Show that the intensity reduces by 75 per cent after a distance of `((In 4)/α)`
(ii) Attenuation of a signal can be expressed in decibel (dB) according to the relation dB = `10 log_10 (I/I_0)`. What is the attenuation in dB/km for an optical fibre in which the intensity falls by 50 per cent over a distance of 50 km?
