An audio signal of 15 kHz frequency cannot be transmitted over long distances without modulation, because (a) The size of the required antenna would be at least 5 km which is not convenient (b) The audio signal cannot be transmitted through sky waves (c) The size of the required antenna would be at least 20 km, which is not convenient (d) Effective power transmitted would be very low, if the size of the antenna is less than 5 km

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Physics NCERT Exemplar Solutions Class 12th Chapter Fifteen Physics Class 12th Communication Systems

An audio signal of 15 kHz frequency cannot be transmitted over long distances without modulation, because
(a) The size of the required antenna would be at least 5 km which is not convenient
(b) The audio signal cannot be transmitted through sky waves
(c) The size of the required antenna would be at least 20 km, which is not convenient
(d) Effective power transmitted would be very low, if the size of the antenna is less than 5 km

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alok kumar singh | Contributor-Level 10

4 months ago

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- a, b, d

Explanation- frequency is given by Vm=15KHz

So wavelength is given by $? = \frac{c}{v} = \frac{3 * 10^{8}}{15 * 10^{3}} = \frac{1}{5} * 10^{5} m$

Also we know that l = $? / 4$ = 5km

The audio signals are of low frequency waves. Thus, they cannot be transmitted through sky

Waves as they are absorbed by atmosphere.

If the size of the antenna is less than 5 km, the effective power transmission would be very

Low because of deviation from resonance wavelength of wave and antenna length.

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