Tag: communication system

Quizzes (2) Questions (53)

Questions Related to communication system

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Thermal noise is generated in:

  1. transistors and diodes

  2. resistors

  3. copper wire

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermal noise or Nyquist noise is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.

In each of the options, an electrical element is used and hence this noise is produced in all these elements. The correct option is option D

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Long distance short-wave radio broadcasting uses:

  1. ground wave

  2. ionospheric waves

  3. direct wave

  4. sky wave
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Shortwave radio or radio waves are used for broadcasting of voice and music to listeners over very large areas. Which uses a layer in the atmosphere called the ionosphere for the refraction and reflection purpose.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

A $8\ kHz$ communication channel has an $SNR$ of $30\ dB$. If the channel bandwidth is doubled, keeping the signal power constant, the $SNR$ for the modified channel will be

  1. $27\ dB$

  2. $30\ dB$

  3. $33\ dB$

  4. $60\ dB$.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

SNR in dB is 10*log10(S/N). If bandwidth doubles, noise power N doubles (assuming white noise), so S/N becomes S/(2N). The new SNR is 10*log10(S/2N) = 10*log10(S/N) - 10*log10(2) = 30 - 3 = 27 dB.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

A signal of frequency 20 kHz and the peak voltage of 5 Volt is used to modulate a carrier wave of frequency 1.2 MHz and peak voltage 25 Volts. Choose the correct statement. 

  1. Modulation index = 5, side frequency bands are at 1400 kHz and 1000 kHz.

  2. Modulation index = 0.8, side frequency bands are at 1180 kHz and 1220 kHz.

  3. Modulation index = 5 , side frequency bands are at 21.2 kHz and 18.8 kHz.

  4. Modulation index = 0.2, side frequency bands are at 1220 kHz and 1180 kHz.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Modulation index m = Vm/Vc = 5/25 = 0.2. Sidebands are at fc + fm and fc - fm, which are 1200 + 20 = 1220 kHz and 1200 - 20 = 1180 kHz.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Assertion(A): The microphone acts as a transducer.
Reason(R) : In radio communication, microphone is used to convert sound signal into electrical signal.

  1. A and R are true and R is the correct explanation of A

  2. A and R are true but R is not correct explanation of A

  3. A is true but R is false

  4. A is false but R is true.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A device which converts energy in one form to another is called a transducer. Usually a transducer converts a signal in one form of energy to a signal in another. The process of converting one form of energy to another is known as transduction.
In radio communication, microphone is used to convert sound signal into electrical signal. Hence the microphone acts as a transducer.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Match the following: 

Name of device Usage
a. Antenna e. sends out information
b. Transmitter f. picks up information
c. Receiver g. converts energy in one form to another form
d. Transducer h. radiates signal
i. recieves signal

  1. a-e; b-g,h; c-f; d-h

  2. a-h,i; b-e; c-f; d-g

  3. a-f; b-e; c-f,i; d-h

  4. a-h; b-g,i; c-f; d-e
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to definitions use in communication systems: 
Antenna: A device that radiates signals. (Option h)
Transmitter: As the name suggests, it transmits (sends) out information. (Option e)
Receiver: As the name suggests recieves (pick ups) the information. (Option f)
Transducer: A device that converts variations in a physical quantity, such as pressure or brightness, into an electrical signal, or vice versa. That is option g.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

To double the covering range of a TV transmittion tower, its height should be multiplied by:

  1. 4

  2. 2

  3. $\sqrt { 2 } $

  4. $\dfrac { 1 }{ \sqrt { 2 } } $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The range of a TV tower is d = sqrt(2*R*h). To double d, the height h must be multiplied by 4, because sqrt(4) = 2.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

The waves emitted by a radio transmitter are 

  1. linearly polarised

  2. unpolarised

  3. monochromatic

  4. elliptically polarised
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Waves emitted by a radio transmitter are usually linearly polarized. The vertical antennas that are used for radio broadcasting emit waves that, in a horizontal plane around the antenna, are polarized in the vertical direction parallel to the antenna.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Three amplifiers  $X , Y$  and  $Z$  are connected in series.If the voltage gains of  $X , Y$  and  $Z$  are  $10,20$  and  $30$  respectively and the input signal is 1 mV peak value,then what is the output signal voltage (peak value,dc supply voltage is  $10\mathrm { V }$ ?

  1. $4 \mathrm { V }$

  2. $5 \mathrm { V }$

  3. $6 \mathrm { V }$

  4. $7 \mathrm { V }$
Reveal answer Fill a bubble to check yourself
A Correct answer