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Questions Related to physics

Multiple choice physics sound types of waves sound as a wave of disturbance sound waves are longitudinal waves

A longitudinal wave is a wave that consists of oscillations that are 

  1. perpendicular to the direction of wave propagation

  2. parallel to the direction of wave propagation

  3. radial to the direction of wave propagation

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A longitudinal wave is a wave that consists of oscillations that are perpendicular to the direction of wave propagation

The correct option is (b)

Multiple choice physics study of sound conditions for hearing echo echo ultrasound and its applications

An echo will be heard if the minimum distance between the source of sound and the obstacle is :

[assume air to be the medium]

  1. $1\;m$
  2. $10\;m$
  3. $15\;m$
  4. $17\;m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 344 m/s at a given temperature, say at 22 $^0 C $ in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1 s. 


Hence, the total distance covered by the sound from the point if generation to
the reflecting surface and back should be at least 

$344 \times 0.1= 34.4 m.$

Thus for hearing distinct echoes, the minimum distance pf the obstacle from 
the source of sound must be half this distance

That is, $\frac{34.4}{2}=17.2\,m \approx 17\,m$

Multiple choice physics study of sound conditions for hearing echo echo ultrasound and its applications

Bats detect the obstacle in their path by receiving the detected

  1. Infrasonic waves

  2. Ultrasonic waves

  3. Both

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Bats can produce ultrasonic waves by flapping their wings. They can also detect these waves.these waves produced by the bats after reflection from the obstacles like building guide them to  remain away from the obstacles during night with the help of ultrasonic waves.

Multiple choice physics study of sound conditions for hearing echo echo ultrasound and its applications

The technique used by bats to find their way or to locate food is _______.

  1. SONAR

  2. RADAR

  3. Echolocation

  4. Flapping
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Bats can produce ultrasonic waves by flapping their wings. They can also detect these waves.these waves produced by the bats after reflection from the obstacles like building guide them to  remain away from the obstacles during night with the help of ultrasonic waves.

Multiple choice physics study of sound conditions for hearing echo echo ultrasound and its applications

It has been seen that the behaviour of animals becomes unusual just before the tremor is felt.what is the reason behind this?

  1. Because animals are able to detect infrasonic waves produced at the time of tremor.

  2. Because animals are able to detect ultrasonic waves produced at the time of tremor.

  3. Because animals are able to detect audible waves produced at the time of tremor.

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

Has been seen that the behaviour of animals becomes unusual just before the tremor is felt.This is because animals are able to detect infrasonic waves produced at the time of tremor. Infrasonic waves are waves of frequency less than 20Hz.

Multiple choice physics static electricity explaining static electricity charging by induction electric charges and fields

The number of electrons that must be removed from an electrically neutral silver dollar to give it a charge of $+2.4C$ is

  1. $2.5\times { 10 }^{ 19 }$
  2. $1.5\times { 10 }^{ 19 }$
  3. $1.5\times { 10 }^{ -19 }$
  4. $2.5\times { 10 }^{ -19 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Total charge, $q=+2.4C$
Then by quantization of charge $q=ne$
$\therefore$ number of electrons, $\quad n=\cfrac { q }{ e } =\cfrac { 2.4C }{ 1.6\times { 10 }^{ -19 } } =1.5\times { 10 }^{ 19 }\quad \quad $