Frequency of a Wave

Q. A modu action frequency an AM radio station is $250\text{kHz}$, which is $10\%$ of the carrier wave. If another AM station approaches you for license, what broadcast frequency will you allot ?

1. $2750\text{kHz}$
2. $2900\text{kHz}$
3. $2250\text{kHz}$
4. $2000\text{kHz}$

Q. A $1.0m$ long metallic rod is rotated with an angular frequency of $400\text{rad/s}$ about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of $0.5T$ parallel to the axis exists everywhere. Calculate the emf developed between the centre and the ring.

Q. In an amplitude modulated wave for audio-frequency of $500$ cycles/second, the appropriate carrier frequency can be

1. $50\text{cycles/sec}$.
2. $500\text{cycles/sec}$
3. $100\text{cycles/sec}$.
4. $50,000\text{cycles /sec}$

Q. A bandwidth of $6\text{MHz}$ is available for A.M. transmission. If the maximum audio signal frequency used for modulating the carrier wave is not to exceed $6\text{KHz}$ . The number of stations that can be broadcasted within this band simuntaneosuly without interfering with each other will be

Q. $100MHz$ FM carrier wave frequency is modulated by $10kHz$ sinusoidal modulating signal. If the maximum frequency deviation is $50kHz$, what is the value of modulation index?

1. 10
2. 20
3. 2.5
4. 5

Q. On a particular day, the maximum frequency reflected from the ionosphere is $10\text{MHz}$. On another day, it was found to increase to $11\text{MHz}$. Calculate the ratio of maximum electron density of the ionosphere on the two days.

1. $1.21$
2. $1.44$
3. $0.88$
4. $1.69$

Q. What are the components in a communication channel?

Q. The number of amplitude modulated broadcast stations that can be accommodated in a $300kHz$ band width for the highest modulating frequency $15kHz$ will be:

1. $20$
2. $10$
3. $8$
4. $15$

Q. A carrier signal $C\left(t\right)=25\sin (2.512\times {10}^{10}t)$ is amplitude modulated by a message signal $m\left(t\right)=5\sin (1.57\times {10}^{8}t)$ and transmitted through an antenna. What will be bandwidth of the modulated signal?

1. $1987.5\text{MHz}$
2. $2.01\text{GHz}$
3. $50\text{MHz}$
4. $8\text{GHz}$

Q. In an FM system a $7kHz$ signal modulated $108MHz$ carries so that frequency deviation is $50Hz$. The carrier swing is

1. $0.71$
2. $8$
3. $7.143$
4. $350$

Q. The modulation frequency Of an AM radio station is 250 KHz, which is 10% of the carrier wave. If another AM station approaches you for licence what broadcast frequency will you allot?

1. 2750 KHz
2. 2250 KHz
3. 2900 KHz
4. 2000 KHz

Q. If frequency of a message signal is 4 kHz, then the number of channels that can be accomadated in 80 kHz bandwidth when AM modulation technique is used is

1. 20
2. 10
3. 8
4. 4

Q. In a microwave oven the device used for generating microwaves is

1. Stirrer fan
2. Metal wall
3. Magnetron
4. Cyclotron

Q. Frequencies of UHF ranges normally propagated by means of

1. ground waves
2. space waves
3. sky waves
4. surface waves

Q. A sinusoidal carrier wave of amplitude $40$V is amplitude modulated by a sinusoidal signal voltage. What is the amplitude of each side band if the modulation index is $25\%$.

1. $50$V
2. $4$V
3. $6$V
4. $8$V

Q. A signal of $5kHz$ frequency is amplitude modulated on a carrier wave of frequency $2MHz$. Frequencies of the resultant signal is/are

1. $2MHz$ only
2. $2005kHz$ and $1995kHz$
3. $2005kHz$, $2000kHz$ and $1995kHz$
4. $2000kHz$ and $1995kHz$

Q. Effective power radiated by a long wavelength baseband signal would be small.

1. True
2. False

Q. Which of the following is incorrect?

1. Our headphones are a kind of transducer
2. Loss of strength of a signal while propagation is called attenuation
3. Original low frequency message can be tranmitted to long distance
4. Noise refers to unwanted signals that tend to disturb transmission

Q. The basic telephone channel has a bandwidth of.

1. $2700$ Hz
2. $2400$ Hz
3. $1200$ Hz
4. $3100$ Hz

Q. A massless rod is suspended by two identical strings AB and CD of equal length. A block of mass $m$ is suspended from point $O$ such that BO is equal to $x^{\prime }$. Further, it is observed that the frequency of lst harmonic (fundamental frequency) in AB is equal to $2^{nd}$ harmonic frequency in CD. Then, length of BO is

1. $L/5$
2. $4L/5$
3. $3L/4$
4. $L/4$

Q. A $1000kHz$ carrier is simultaneously modulated with $300Hz$, $800Hz$ and $2kHz$ audio waves. The frequencies present in the output is

1. $999.7KHz$, $100.3KHz$, $999.2KHz$
2. $1000.8KHz$, $998KHz$, $1002KHz$
3. $1000.7KHz$, $998KHz$, $1002KHz$
4. both (a) and (b)

Q. The length of the antenna required for the transmission of frequencies of EM waves with bandwidth having AF range is

1. 15 km
2. 375 m
3. 1500 m
4. 3.75 km

Q. A source X of unknown frequency produces 8 beats per second with a source of 250 Hz and 12 beats per second with a source of 270 Hz . The frequency of the source X is :

1. 242 Hz
2. 258 Hz
3. 262 Hz
4. 282 Hz

Q. In which year, the radio broadcasting had started in India?

1. 1928
2. 1925
3. 1926
4. 1927

Q. On a particular day, the maximum frequency reflected from the ionosphere is $10\text{MHz}$. On another day, it was found to increase to $11\text{MHz}$. Calculate the ratio of maximum electron density of the ionosphere on the two days.

1. $1.21$
2. $1.44$
3. $0.88$
4. $1.69$

Q. When tension in a string is 225 N, then vibrating in fundamental mode it produces 6 beats per second with a tuning fork. The same string, when under tension of 256 N, again vibrating in fundamental mode produces with the same tuning fork 6 beats per second. Then, the frequency of the tuning fork is:

1. 256 Hz
2. 255 Hz
3. 240 Hz
4. 186 Hz

Q. An unknown frequency source $X$, produces $8$ beats with another source of frequency $270Hz$. The frequency of source $X$ will be ?

1. $282Hz$
2. $262Hz$
3. $242Hz$
4. $258Hz$

Q. For high frequency signals, small antenna is required.

1. False
2. True

Q. The audio signal voltage is given by $V_m=2sin12\pi \times {10}^{3}t$ . The bandwidth and LSB if carrier wave has a frequency $3.14\times {10}^{6}rad/s$

1. 6 KHz; 494 KHz
2. 18 KHz; 494 KHz
3. 12 KHz; 494 KHz
4. 6 KHz; 313 KHz

Q. is the loss of strength of a signal while propagating through a medium.

1. Amplification
2. Modulation
3. Attenuation