Creating AM

Q.

What is a modem?

Q. A carrier wave of peak voltage 12V is used to transmit a messagesignal. What should be the peak voltage of the modulating signal inorder to have a modulation index of 75%?

Q.

If a message signal of frequency$f_m$ is amplitude modulated with a carrier signal of frequency $f_c$ and radiated through an antenna, the wavelength of the corresponding signal in the air is:

Given, $C$ is the speed of electromagnetic waves in vacuum/air

1. $\frac{C}{\left(f_c+f_m\right)}$

2. $\frac{C}{\left(f_c-f_m\right)}$

3. $\frac{C}{f_m}$

4. $\frac{C}{f_c}$

Q. A signal $A\cos \omega t$ is transmitted using $v_0\sin {\omega }_{0}t$ as carrier wave. The correct amplitude modulated $\left(AM\right)$ signal is

1. $v_0\sin \left[{\omega }_0\right(1+0.1A\sin \omega t\left)t\right]$
2. $v_0\sin {\omega }_{0}t+A\cos \omega t$
3. $v_0\sin {\omega }_{0}t+$
   $\frac{A}{2}\left[\sin \right({\omega }_0-\omega )t+\sin ({\omega }_0+\omega \left)t\right]$
4. $(v_0+A)\cos \omega t\sin {\omega }_{0}t$

Q. Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be $3.57V$. The threshold frequency of the material is

1. $2.5\times {10}^{15}\text{Hz}$
2. $1.6\times {10}^{15}\text{Hz}$
3. $5\times {10}^{15}\text{Hz}$
4. $4\times {10}^{15}\text{Hz}$

Q.

In amplitude modulation the bandwidth is

1. equal to the signal frequency

2. Twice the signal frequency

3. Thrice the signal frequency

4. Four times the signal frequency

Q.

What is PAM PWM PPM?

Q.

If the highest frequency modulating a carrier is $5\mathrm{kHz}$, then the number of AM broadcast stations accommodated in a $90\mathrm{kHz}$ bandwidth is ___________.

Q. The electric dipole potential at a large distance $r$ from the dipole falls off. The falling off the magnitude of the electric potential depends on,

1. $\frac{1}{r^3}$
2. $\frac{1}{r}$
3. $\frac{1}{r^2}$
4. $\frac{1}{r^4}$

Q. An antenna current of an AM broadcast transmitter modulated by 50% is 11 A. The carrier current is

1. 10.35 A
2. 9.25 A
3. 10 A
4. 5.5 A

Q.

What happens when modulation index is greater than one?

Q. A modulating signal is a square wave, as shown in Fig. 15.14.The carrier wave is given by c t( ) 2 sin(8 ) = πt volts.(i) Sketch the amplitude modulated waveform(ii) What is the modulation index?

Q.

Why do birds fly off a high tension wire when the current is switched on?

Q. We do not transmit low frequency signal to long distance because-

(a) The size of the antenna should be comparable to signal wavelength which is unreal solution for a signal of longer wavelength
(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 long distances by superimposing with a high frequency wave as well

Therefore, the most suitable option will be:

1. (a), (b) and (c) are true only
2. (a), (c) and (d) are true only
3. (b), (c) and (d) are true only
4. All statements are true

Q. The process of superimposing signal frequency (i.e. audio wave) on the carrier wave is known as

1. Transmission
2. Detection
3. Reception
4. Modulation

Q. The de Broglie wavelength of a photon is twice the de Broglie wavelength of an electron. The speed of the electron is $v_e=\frac{c}{100}$ Then,

1. $\frac{E_e}{E_p}={10}^{-4}$
   
   
2. $\frac{E_e}{E_p}={10}^{-2}$
   
3. $\frac{p_e}{m_{e}c}={10}^{-4}$
4. $\frac{p_e}{m_{e}c}={10}^{-2}$
   
   

Q. For an amplitude modulated wave, the maximum amplitude is foundto be 10V while the minimum amplitude is found to be 2V. Determinethe modulation index, μ.

Q.

For an amplitude modulated wave, the maximum amplitude is found to be $9V$ while the minimum amplitude is found to be $3V$. The modulation index is____________

1. $100\%$

2. $75\%$

3. $50\%$

4. $25\%$

Q.

Briefly Explain About Amplitude Demodulation

Q.

What happens in over modulation?

Q.

What are the disadvantages of harmonics?

Q.

A modulating signal is a square wave, as shown in Fig. 15.14.

The carrier wave is given by

(i) Sketch the amplitude modulated waveform

(ii) What is the modulation index?

Q.

For sustained interference, we need two sources that emit wave of

Q. In a carrier frequency of 100kHz and a modulating frequency of 5kHz. What is the bandwidth of AM transmission

Q. A transmitter supplies 9 kW to the aerial when unmodulated. The power radiated when modulated to 40% is

1. 5 kW
2. 10 kW
3. 9.72 kW
4. 12 kW

Q. Which sample, $A$ or $B$ shown in figure has shorter mean-life?

Q.

1 Angstrom unit (Å) is equal to:

1. 10^-10m

2. 10^-12m

3. 10^-1m

4. 10^-6m

Q. In a closed organ pipe , the fundamental frequency is $n$. What will be the ratio of frequencies of the next three overtones?

1. $3:5:7$
2. $3:4:5$
3. $3:7:11$
4. $2:3:4$

Q. A carrier is simultaneously modulated by two sine waves with modulation indices of 0.4 and 0.3. The resultant modulation index will be

1. 1
2. 0.7
3. 0.5
4. 0.35

Q. Let $E_n=\frac{-1}{8{\epsilon }_0^2}\frac{m{e}^4}{n^2{h}^2}$ be the energy of the $n^{th}$ level of $H$- atom. If all the $H$- atoms are in the ground state and radiation of frequency $(E_2–E_1)/h$ falls on it.

1. no atoms will make a transition to the $n=3$ state.
2. all atoms will be excited to the $n=2$ state.
   
3. it will not be absorbed at all
   
4. some of atoms will move to the first excited state.