Tag: physics

Questions Related to physics

Thermal noise is generated in:

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

  1. transistors and diodes

  2. resistors

  3. copper wire

  4. all of the above

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Correct Option: D
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

Long distance short-wave radio broadcasting uses:

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

  1. ground wave

  2. ionospheric waves

  3. direct wave

  4. sky wave

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Correct Option: B
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.

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

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

  1. $27\ dB$

  2. $30\ dB$

  3. $33\ dB$

  4. $60\ dB$.

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Correct Option: A

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. 

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

  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.

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Correct Option: D

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

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

  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.

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Correct Option: A
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.

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

  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

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Correct Option: B
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.

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

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

  1. 4

  2. 2

  3. $\sqrt { 2 } $

  4. $\dfrac { 1 }{ \sqrt { 2 } } $

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Correct Option: A

The waves emitted by a radio transmitter are 

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

  1. linearly polarised

  2. unpolarised

  3. monochromatic

  4. elliptically polarised

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Correct Option: A
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.

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  $10\mathrm { V }$ ?

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

  1. $4 \mathrm { V }$

  2. $5 \mathrm { V }$

  3. $6 \mathrm { V }$

  4. $7 \mathrm { V }$

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Correct Option: A

Which  signal will be heard first ? 

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

  1. Person yelling from a 100 m away

  2. Radio signal from 100 m away

  3. Both at the same time

  4. None of the above.

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Correct Option: A