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2 months ago

Communication Systems Physics NCERT Exemplar Solutions Class 12th Chapter Fifteen

Find the modulation index of an AM wave having 8V variation where maximum amplitude to the wave is 9V.

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Vishal Baghel

Contributor-Level 10

Modulation Index, $μ = \frac{A_{m}}{A_{C}}$

Variation = $2 A_{m} = 8 \Rightarrow A_{m} = 4 v$

$A_{m} + A_{c} = 9$

$A_{C} = 9 - A_{m} = 5 v$

$∴ μ = \frac{4}{5} = 0.8$

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2 months ago

Communication Systems Class 12th

Find the modulation index of an AM wave having 8V variation where maximum amplitude to the wave is 9V.

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2 months ago

Communication Systems Class 12th

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

(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 log distances by superimposing with a high frequency wave as well.

Therefore, the most suitable options will be

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New answer posted

2 months ago

Communication Systems Physics NCERT Exemplar Solutions Class 12th Chapter Fifteen

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

(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 log distances by superimposing with a high frequency wave as well.

Therefore, the most suitable options will be

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Payal Gupta

Contributor-Level 10

For high wavelength, size of antenna should be high.

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4 months ago

Communication Systems Class 12th

Suppose a n-type wafer is‘created by doping Si crystal having 5 x 10²⁸atoms/m³ with 1 ppm concentration of As. On the surface 200 ppm boron is added to create ‘p’ region in this wafer. Considering n_i = 1.5 x 10¹⁶ m^-3,
(i) Calculate the densities of the charge carriers in the n and p regions,
(ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

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4 months ago

Communication Systems Class 12th

Which of the following would produce analog signals and which would produce digital signals?
(a) A vibrating tuning fork
(b) Musical sound due to a vibrating sitar string
(c) Light pulse
(d) Output of NAND gate

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Analog and digital signals are used to transmit information, usually through electric signals. In both these technologies, the information such as any audio or video is

transformed into electric signals.

The difference between analog and digital technologies is that in analog technology, information is translated into electric pulses of varying amplitude. In digital technology, translation of information is into binary formal (zero or one) where each bit is representative of two distinct amplitudes.

Thus, (a) and (b) would produce analog signal and (c) and (d) would produc

...more

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4 months ago

Communication Systems Class 12th

In amplitude modulation, the modulation index m is kept less than or equal to 1 because
(a) m> 1, will result in interference between carrier frequency and message frequency, resulting into distortion.
(b) m > 1, will result in overlapping of both side bands resulting into loss of information
(c) m > 1, will result in change in phase between carrier signal and message signal.
(d) m > 1, indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion.

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- b, d

Explanation- modulation index m= A_m/A_c

If m>1 then A_m>A_c

maximum modulation frequency m_f= frequency deviation / maximum frequency of modulating wave

here if m>1 then it means overlapping of both sides resulting loss of information.

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4 months ago

Communication Systems Class 12th

The frequency response curve (figure) for the filter circuit used for production of AM wave should be

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- a, b, c

Explanation- production of modulated wave is given by frequency of upper side band – frequency of lower side band so in first three cases it is clearly visible.

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4 months ago

Communication Systems Class 12th

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 x 10⁶m)
(a) 100 km (b) 24 km (c) 55 km (d) 50 km

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer-b, c, d

Explanation- height of tower= 240m

For line of sight communication maximum distance would be d= $\sqrt[]{2 R h}$

So d= $\sqrt[]{2 * 6.4 * 10^{6} * 240}$ = 55.4km

So distance under this are communicable

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4 months ago

Communication Systems Class 12th

Audio sine waves of 3 kHz frequency are used to amplitude modulate a carrier signal of 1.5 MHz. Which of the following statements are true?
(a) The side band frequencies are 1506 kHz and 1494 kHz

(b) The bandwidth required for amplitude modulation is 6 kHz

(c) The bandwidth required for amplitude modulation is 3 MHz

(d) The side band frequencies are 1503 kHz and 1497 kHz

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alok kumar singh

Contributor-Level 10

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- b, d

Explanation- w_m=3KHz

And w_c= 1.5MHz= 1500KHz

By using these two 1500 $?$ 3= 1503 and 1497

Bandwidth = 2w_m= 2 $* 3$ = 6KHz

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