Class 12th

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.

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.

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= $\sqrt[]{2Rh}$

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

So distance under this are communicable

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

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.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Explanation-equation of modulating wave is, m (t)= A_msinw_mt

Carrier wave equation is C_m (t)= (A_c+A_msinw_mt)sinw_ct

 = A_c [1+ $\frac{A_m}{A_c}sin{w}_{m}t$ ]sinw_ct

Also $\frac{A_m}{A_c}$ = M

C_mt= (A_c+A_{c $*\propto sin{w}_{m}t$} )sinw_ct

Ac $*\propto$ =K

Sinw_mt= V_m

equation having phase $\varnothing$

so equation is A_c+K₂V_mt}+sinw_ct+ $?$ ]

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- b

Explanation- it is represented by a diagram given below

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- b

Explanation- Here, in this question, the frequency of modulated signal received becomes more, which is possible with the poor bandwidth selection of amplifiers.

This happens because bandwidth in amplitude modulation is equal to twice the

Frequency of modulating signal. But, the frequency of male voice is less than that of a female.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- c

Explanation- The device which follows square law is used for modulation purpose. Characteristics shown by (i) and (iii) corresponds to linear devices.

Characteristics shown by (ii) corresponds to square law device. Some part of (i) also

Follow square law.

Hence, (ii)and (iv) can be used for modulation.

This is a Multiple Choice Questions as classified in NCERT Exemplar

Answer- b

Explanation- frequency of career wave and frequency of amplitude modulated wave is same which is w_c .