Tag: physics

Questions Related to physics

Ultrasound is sound above the human hearing range. It can be heard by

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. Bats

  2. Elephants

  3. Lions

  4. Sheep

Show answer
Correct Option: A
Explanation:

Among the following , only Bats can hear this sound and Bat uses this sound for their hunting.

An animal which navigates and finds food by echolocation is.

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. bat

  2. frog

  3. tiger

  4. lizard

Show answer
Correct Option: A
Explanation:

Answer is A.

Bats send out sound waves using their mouth or nose.  When the sound hits an object an echo comes back. The bat can identify an object by the sound of the echo. They can even tell the size, shape and texture of  a tiny insect from its echo. Most bats use echolocation to navigate in the dark and find food.

The use of ultrasound waves to investigate the action of the heart is called.

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. ultrasonography

  2. echocardinology

  3. echolocation

  4. echocardiography

Show answer
Correct Option: D
Explanation:

Answer is D.

Technique of echocardiography is based on reflection property of ultrasonic waves.
An echocardiogram (also called an echo) is a type of ultrasound test that uses high-pitched sound waves that are sent through a device called a transducer. The device picks up echoes of the sound waves as they bounce off the different parts of our heart. These echoes are turned into moving pictures of our heart that can be seen on a video screen.

From below who cannot hear ultrasonic sounds?

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. Humans

  2. Bats

  3. Dogs

  4. Deer

Show answer
Correct Option: A
Explanation:

Ultrasonic sounds having frequency above 20,000 Hz  cannot be heard by humans. But Bats , deer and dogs have the ability to hear those sounds. 

The ultrasound waves have a much greater penetrating power than ordinary sound because they have very high

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. Amplitude

  2. Frequency

  3. Wave length

  4. Speed

Show answer
Correct Option: B
Explanation:

The frequency $f$ is related with intensity $I$ of wave by ,

           $I\propto f^{2}$ ,
and intensity is related with energy $E$ by ,
          $E\propto I$ ,
therefore due to high frequency ultrasound has a greater energy than ordinary sound wave , hence greater penetrating power because penetrating power depends upon energy of the wave .

Mark the correct statement:

physics medical imaging ultrasonic sound using ultrasound in medicine ultrasound and its applications

  1. Human beings cannot hear ultrasound.

  2. Dogs, bats and dolphins can hear ultrasound.

  3. Ultrasound have short wavelength.

  4. All

Show answer
Correct Option: D
Explanation:

The sound waves having frequency higher than 20,000 Hz is

called ultrasonic waves. Human beings can"t hear Ultra sound. Bats and dolphins detect the presence of any obstacle by

hearing the echo of the sound produced by them.

A molecule of gas in a container hits one wall (1) normally and rebounds back. It suffers no collision and hits the opposite wall (2) which is at an angle of $30^o$ with wall 1.
Assuming the collisions to be elastic and the small collision time to be the same for both the walls, the magnitude of average force by wall 2. $(F _2)$ provided the molecule during collision satisfy

physics behaviour of perfect gas and kinetic theory of gases mean free path law of equipartition of energy and mean free path behavior of perfect gas and kinetic theory

  1. $F _1 > F _2$

  2. $F _1 < F _2$

  3. $F _1=F _2$, both non-zero

  4. $F _1=F _2=0$

Show answer
Correct Option: A
Explanation:

Initial momentum, $P _1=mvcos 30$
and final momentum, $P _2 = mvcos30$
change in momentum
$\Delta P = -2mv cos30$
$\Delta P =-\sqrt 3 mv$
Force on wall-1
$F _1=\frac {2mv}{\Delta t}$
Force on wall-2
$F _2=\frac {\sqrt 3mv}{\Delta t}$, so $F _1 > F _2$

Mean free path depends on which of the following?

physics behaviour of perfect gas and kinetic theory of gases mean free path law of equipartition of energy and mean free path behavior of perfect gas and kinetic theory

  1. size of the molecule

  2. density of the molecule

  3. diameter of the molecule

  4. All of the above

Show answer
Correct Option: D
Explanation:

The mean free path or average distance between collisions for a gas molecule may be estimated from kinetic theory.

Mean free path displays linear proportionality to the temperature and inverse proportionality to the pressure and molecular diameter.
Mathematically it is expressed as:
$l.p=\dfrac{kT}{\sqrt{2}\pi d _m^2}$

A gas has an average speed of 10 m/s and a collision frequency of 10 $s^{-1}$. What is its mean free path?

physics behaviour of perfect gas and kinetic theory of gases mean free path law of equipartition of energy and mean free path behavior of perfect gas and kinetic theory

  1. $1m$

  2. $2 m$

  3. $3 m$`

  4. $4m$

Show answer
Correct Option: A
Explanation:

The collision frequency $(f)$ is the ratio of rms velocity $(v _{rms})$ to mean free path $(\lambda)$.

Here, collision frequency $f=10 s^{-1}$ and $v _{avg}=10 m/s$
So, $v _{rms}=\sqrt{v _{avg}^2}=\sqrt{10^2}=10 m/s$
Thus, mean free path $\lambda =\dfrac{v _{rms}}{f}=\dfrac{10}{10}=1 m$

If the pressure in a closed vessel is reduced by drawing out some gas, the mean-free path of molecules :

physics behaviour of perfect gas and kinetic theory of gases mean free path law of equipartition of energy and mean free path behavior of perfect gas and kinetic theory

  1. is decreased

  2. is increased

  3. remains unchanged

  4. increases or decreases according to the nature of the gas

Show answer
Correct Option: B
Explanation:

The mean-free path of molecule is the distance traveled by a molecule in two consecutive collision. If pressure is reduced and there are less particle then a molecule will travel longer distance before collision, so mean free path is increased.