Bandwidth of Channels

Q. A proton, a neutron, an electron and an $\alpha -\text{particle}$ have same energy. Then their de Broglie wavelengths compare as

1. ${\lambda }_{\alpha }<{\lambda }_p={\lambda }_n<{\lambda }_e$
   
   
2. ${\lambda }_e={\lambda }_p={\lambda }_n={\lambda }_{\alpha }$
   
3. ${\lambda }_c<{\lambda }_p={\lambda }_n>{\lambda }_{\alpha }$
   
   
4. ${\lambda }_p={\lambda }_n>{\lambda }_e>{\lambda }_{\alpha }$
   
   

Q.

Range of frequencies allotted for commercial FM radio broadcast is

1. 88 to 108 MHz

2. 8 to 88 MHz

3. 88 to 108 GHz

4. 88 to 108 kHz

Q. A telephonic communication service is working at carrier frequency of $10GHz$. Only $10\%$ of it is utilized for transmission. How many telephonic channels can be transmitted simultaneously if each channel requires a bandwidth of $5kHz$ ?

1. $2\times {10}^5$
2. $2\times {10}^6$
3. $2\times {10}^3$
4. $2\times {10}^4$

Q. For television broadcasting, the frequency employed is normally

1. 30-300 MHz
2. 30-300 KHz
3. 30-300 Hz
4. 30-300 GHz

Q. A radio can tune in to any station in the 7.5 MHz to 12 MHz band.What is the corresponding wavelength band?

Q. Assertion :Audio signal of frequency 10 kHz cannot be transmitted over long distance without modulation. Reason: Length of the antenna required $\lambda /4$, should have practical value.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Both Assertion and Reason are incorrect

Q. A telephone link operating at a central frequency of 10 GHz is established. If 1% of this is available then how many telephone channel can be simultaneously given when each telephone covering a band width of 5 kHz

1. 2 X 10⁴
2. 2 X 10⁶
3. 5 X 10⁴
4. 5 X 10⁶

Q. The frequency of a tuning fork ‘$x$’ is $5\%$ greater than that of a standard fork of frequency ‘$K$’. The frequency of another fork ‘$y$’ is $3\%$ less than that of ‘$K$’. When ‘$x$’ and ‘$y$’ are vibrated together $4$ beats are heard per second. The frequencies of $x$ and $y$ are

1. 52.5Hz, 48.5Hz
2. 57.5Hz, 47.5Hz
3. 40.5Hz, 42.5Hz
4. 38.5Hz, 48.5Hz

Q. What is the frequency range of signals that propagates best over the surface of earth?

Q. A string is fixed at both ends vibrates in a resonant mode with a separation $2.0cm$ between the consecutive nodes. For the next higher resonant frequency, this separation is reduced to $1.6cm$. The length of the string is

1. $4.0cm$
2. $8.0cm$
3. $12.0cm$
4. $16.0cm$

Q. Two strings ‘x’ and ‘y’ on a Veena playing the same note are slightly out of tune and produce 6 beats per second. The tension in ‘x’ is slightly decreased and it is found that the beats fall to 3 per second. If the original frequency of ‘x’ is 324 Hz, the frequency of ‘y’ is

1. 318 Hz
2. 330 Hz
3. 518 Hz
4. 618 Hz

Q. The threshold wavelength for a surface having a threshold frequency of $0.6\times {10}^{15}$ Hz is :
given $c=3\times {10}^8$m/s

1. 4000 $A^o$
2. 6000 $A^o$
3. 5000 $A^o$
4. 3500 $A^o$

Q. Match the frequency band with the type of use

Frequency Band	Type of use
a) LF	e) Radio Broad casting
b) HF	f) Marine and navigational aid
c) VHF	g) Satellite communication
d) SHF	h) TV Broad casting

1. a - e; b - f; c - h; d - g
2. a - f; b - e; c- g; d- h
3. a - e; b - g; c - f; d - h
4. a - f; b - e; c - h; d - g

Q. A metal wire of linear mass density of $9.8gm$ is stretched with a tension of $10kg-wt$ betweentwo rigid supports $1$ metre apart. The wire passes at its middle point between the poles of aper magnet and it vibrates in resonance when carrying an alternating current of frequency $n$.The frequency n of the alternating source is

1. $100Hz$
2. $25Hz$
3. $200Hz$
4. $50Hz$

Q. Expression for the relation between (k.e)max and e mue (threashold frequency)

Q. why it is important to convert low frequency messagee to high frequency message before transmission ?

Q. What is the frequency of $A.C.$ supply in India?

Q. State three important factors showing the need for translating a low frequency signal into a high frequency wave before transmission.

Q. A source x of unknown frequency produces 8 beats with a source of 250 Hz and 12 beats with a source of 270 Hz. The frequency of source x is

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

Q. A black body is at a temperature of $5760K$. The energy of radiation emitted by the body at wavelength $250nm$ is $U_1$, at wavelength $500nm$ is $U_2$ and that at $1000nm$ is $U_3$. Wein's constant, $b=2.88\times {10}^{6}nmK$. Which of the following is correct?

1. $U_1>U_2$
2. $U_3=0$
3. $U_2>U_1$
4. $U_1=0$

Q. For TV transmission, the frequency range employed is:

1. $30-300MHz$
2. $30-300KHz$
3. $30-300GHz$
4. $30-300Hz$

Q. A Tuning fork ‘A’ produces 6 beats per second with another fork ‘B’. On loading ‘B’ with a little wax, it produces 5 beats per second with ‘A’. If the frequency of ‘A’ is 256 Hz, the frequency of ‘B’ is:

1. 262 Hz
2. 250 Hz
3. 256 Hz
4. 261 Hz

Q. Band containing all frequencies between upper cuttoff and lower cuttoff frequencies is known as

1. Bandheight
2. Bandlength
3. Bandwidth
4. Length

Q.

The bandwidth sufficient for commercial telephonic communication:

1. 300 Hz

2. 700 Hz

3. 2800 Hz

4. 1400 Hz

Q. A 12KHz message signal with peak voltage 20V is used to modulate a carrier wave of frequency 12MHz and peak voltage 30V. Calculate (i) modulation index (ii) side band frequencies.

Q. write down frequency range for fm and am broadcasting