Tag: physics

Questions Related to physics

Hertz is the unit of

physics measurements and units summary of si units fundamental quantities system of units

  1. wavelength

  2. amplitude

  3. frequency

  4. None of these

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Correct Option: C
Explanation:

Hertz is the fundamental unit of frequency.

The SI unit of electron mobility is  :

physics measurements and units summary of si units fundamental quantities system of units

  1. ${M^2}{S^{ - 1}}V - 1$

  2. $=m^2 s^{-1}V^{-1}$

  3. $m{s^{ - 1}}V$

  4. ${m^2}{s^{ - 2}}V$

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Correct Option: B
Explanation:

Electron mobility:- It is the ratio of velocity to electric field.

$\mu=\dfrac{v _e}{E}$. . . . . . .(1)
SI unit of velocity, $v _e$ $=m/s$
SI unit of electric field, $E$ $=V/m$
From equation (1),
SI unit of electron mobility is $=\dfrac{m/s}{V/m}$
$=m^2/Vs$
$=m^2 s^{-1}V^{-1}$

The dimensional formula of a physical quantity is $\displaystyle { M }^{ 1 }{ L }^{ 2 }{ T }^{ 3 }{ I }^{ -1 }$ .What is its SI unit?

physics measurements and units summary of si units fundamental quantities system of units

  1. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 3 }{ A }^{ -1 }$

  2. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 2 }{ A }$

  3. $\displaystyle { kg\quad ms }^{ -3 }{ A }^{ 2 }$

  4. $\displaystyle { kg}^{2}{ m }^{ 2 }{ s }^{ 3}{ A }^{ -1 }$

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Correct Option: A
Explanation:

SI unit of $M$ is $kg$, that of $L$ is $m$, $T$ is $s$ and $I$ is $A$.
So, SI unit of $[M^1L^2T^{3}I^{-1}]$ is  $kg \ m^2s^{3}A^{-1}$.

Find the unit of the following derived quantities: 
(a) Force [Hint: Force = Mass $\times$ acceleration]
(b) Pressure $\left[Hint: Pressure =\frac{force}{Area}\right]$

physics measurements and units summary of si units fundamental quantities system of units

  1. $kg\,m\,s^{-2}$ and $kg\,m^{-1}\,s^{-2}$

  2. $kg\,m\,s^{-1}$ and $Kg\,m^{-2}\,s^{-1}$

  3.  $ N$ and $ Pa$

  4. None of these

Show answer
Correct Option: A,C
Explanation:
Force   $F = ma$
So, unit of force is  $kg \ m/s^2$
Newton $(N)$ is also the unit of force.
Pressure   $P = \dfrac{F}{A}$
Unit of pressure   $ = \dfrac{kg \ m/s^2}{m^2} = kg \ m^{-1}s^{-2}$
Also, pressure is measured in Pascal $(Pa)$.

The S.I. unit of magnetic pole strength is_______

physics measurements and units summary of si units fundamental quantities system of units

  1. $A.{ m }^{ 2 }$

  2. $A.{ m }^{ -1 }$

  3. A.m

  4. $A/{ m }^{ 2 }$

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Correct Option: C
Explanation:

Magnetic pole strength is the strength of a magnetic pole to attract magnetic materials towards itself . S.I. unit of magnetic pole strength is Ampere-meter $(A\,m)$.

A disc is rolling on a surface without slipping. What is the ratio of its translational to rotational kinetic energies?

physics turning effects of forces the turning effect of a force moment of force or torque couple

  1. $5:2$

  2. $2:1$

  3. $3:2$

  4. $2:3$

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Correct Option: B
Explanation:
Translational Kinetic Energy$=\cfrac{1}{2}mv^{2}=KE _{T}$
Rotational KE$=\cfrac{1}{2}I\omega^{2}$
$v=r\omega\,\,\,\,,I=\cfrac{1}{2}MR^{2}$
Rotational KE$=\cfrac{1}{2}\times\cfrac{1}{2}mR^{2}\times(\cfrac{v}{R})^{2}$
$KE _{r}=\cfrac{1}{4}mv^{2}$
$\cfrac{KE _{T}}{KE _{r}}=\cfrac{\cfrac{1}{2}mv^{2}}{\cfrac{1}{4}mv^{2}}=2:1$

A solid sphere rolls on horizontal surface without slipping. What is the ratio of its rotational to translation kinetic energy.

physics turning effects of forces the turning effect of a force moment of force or torque couple

  1. $\dfrac {2}{5}$

  2. $\dfrac {5}{2}$

  3. $\dfrac {3}{2}$

  4. $0$

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Correct Option: D

Sound below frequency of 20Hz is known as

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

  1. Ultrasound

  2. Infrasonic

  3. Ultrasonic

  4. None

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Correct Option: B
Explanation:

Sound below frequency of 20Hz is known as Infrasonic

Ultrasound waves have :

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

  1. high frequency and short wavelength

  2. low frequency and short wavelength

  3. high frequency and long wavelength

  4. low frequency and long wavelength

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Correct Option: A
Explanation:

The sound waves having frequency higher than $20kHz$ is called ultrasonic waves. It has short wavelength.

The properties of ultrasound that make it useful is/are 

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

  1. high power and high speed.

  2. high power and good directivity.

  3. high frequency and high speed.

  4. high frequency and bending around the objects.

Show answer
Correct Option: B
Explanation:

Answer is B.
The ultrasonic devices achieve high directivity by modulating audible sound onto high frequency ultrasound. The higher frequency sound waves have a shorter wavelength and thus don't spread out as rapidly. For this reason, the resulting directivity of these devices is far higher than physically possible with any loudspeaker system. However, they are reported to have limited low-frequency reproduction abilities. 
High power ultrasound can break up stony deposits or tissue, accelerate the effect of drugs in a targeted area, assist in the measurement of the elastic properties of tissue, and can be used to sort cells or small particles for research.
Hence, the above characteristics make ultrasound to be very useful.