Tag: physics

Questions Related to physics

The room heater can maintain only ${16^0}C$ in the room when the temperature outside is -${20^0}C$. It is not warm and comfortable, that is why the electric stove with power of 1 kw is also plugged in.Together these two devices maintain the room temperature of ${22^0}C$. Determine the thermal  power of the heater.

physics solar equipment solar power plant production of electricity from solar energy solar power solar energy and its applications generation of electricity

  1. 3kW

  2. 4 kW

  3. 5kW

  4. 6kW

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Correct Option: C

State whether given statement is True or False
Sonar make use of ultrasound.

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Answer is A.
Ultrasound is sound with a frequency higher than 20 kHz. This is above the human range of hearing. The most common use of ultrasound, creating images, has industrial and medical applications.
Sonar illustrates how a ship on the ocean utilizes the reflecting properties of ultrasound waves to determine the depth of the ocean. A ultrasound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This technique is called sonar (originally an acronym for SOund Navigation And Ranging).

In SONAR, we use

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. ultrasonic waves

  2. infrasonic waves

  3. radio waves

  4. audible sound waves

Show answer
Correct Option: A
Explanation:

Answer is A.

Sonar illustrates how a ship on the ocean utilizes the reflecting properties of ultrasound waves to determine the depth of the ocean. A ultrasound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This technique is called sonar (originally an acronym for Sound Navigation And Ranging).

SONAR is

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. SOund Navigation And Ranging

  2. SOund Nullyfying And Ranging

  3. SOund Navigation with Amplitude and Ranging

  4. None

Show answer
Correct Option: A
Explanation:

SONAR is the best example that illustrates how a ship on the ocean utilizes the reflecting properties of sound waves to determine the depth of the ocean. A sound wave is transmitted and bounces off the seabed. Because the speed of sound is known and the time lapse between sending and receiving the sound can be measured, the distance from the ship to the bottom of the ocean can be determined. This technique is called sonar (SOund Navigation And Ranging).

In a good auditorium the reverberation time is

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. 0.17 V/A

  2. > 0.17 V/A

  3. < 0.17 V/A

  4. none of these

Show answer
Correct Option: C
Explanation:

The time for which sound continues to be heard (due to persistence) after the source has stopped producing the sound is called reverberation time . Sabine gave a formula for reverberation time of a good building , which is 

               $T=0.16V/A$ ,
where $V=$ volume of building in cubic metre ,
           $A=$ total absorption of building ,
hence option C is correct .


State whether given statement is True or False
It is usually preferable to have a longer reverberation time in an auditorium for music than one for speeches.

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

The reverberant sound in an auditorium dies away with time as the sound energy is absorbed by multiple interactions with the surfaces of the room. In a more reflective room, it will take longer for the sound to die away and the room is said to be 'live'. In a very absorbent room, the sound will die away quickly and the room will be described as acoustically 'dead'. But the time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer.
The desirable range of reverberation times for general purpose auditoriums is about 1.5 to 2.5 seconds. Longer reverberation times are sometimes desirable for music and shorter reverberation times are better if the auditorium is to be used for speech only.
Rooms used for speech typically need a shorter reverberation time so that speech can be understood more clearly. If the reflected sound from one syllable is still heard when the next syllable is spoken, it may be difficult to understand what was said. On the other hand the reverberation time is too short, tonal balance and loudness may suffer.
Basic factors that affect a room's reverberation time include the size and shape of the enclosure as well as the materials used in the construction of the room. Every object placed within the enclosure can also affect this reverberation time, including people and their belongings.
Hence, a longer reverberation time is preferred in an auditorium for music than one for speeches.

The device/instrument which does not work on the multiple reflections of sound waves is:

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. Mega phone

  2. Sound board

  3. Guitar

  4. Stethoscope

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Correct Option: C
Explanation:

except guitar all the listed instruments work on multiple reflections of sound guitar works on vibration of strings 

so the answer is C.

Why the ceiling of concert halls, cinema halls made curved?

physics study of sound reverberation applications of reflection of sound applications of ultrasound

  1. to make the hall beautiful.

  2. for proper light conditions.

  3. so that the sound can reach all corners properly.

  4. So that the picture or the stage can be visible to each and energy person.

Show answer
Correct Option: C
Explanation:

In concert halls, cinema halls, conference halls, the ceiling are made curved, so that the sound after reflection from the curved surface reaches all corners of the hall evenly.

A radioactive element ${X} _{90}^{238}$ decays into ${Y} _{83}^{222}$. The number of $\beta$-particles emitted are

physics nuclear physics beta decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

  1. 1

  2. 2

  3. 4

  4. 6

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Correct Option: A
Explanation:

The radioactive element undergoes four alpha decays and one beta decay as follows:


$^{238} _{90}X\rightarrow ^{222} _{83}Y+4^4 _2He+ ^{0} _{-1}e$

Clearly only one beta particle (electron) is emitted.

The mass number of an element in a radioactive series is 223. Then the radioactive series is ................

physics nuclei beta decay change in nucleus due to radioactive decay alpha, beta and gamma particles (rays) and their properties

  1. 4n

  2. 4n+3

  3. 4n+2

  4. 4n+1

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Correct Option: B