Tag: motion and measurement

Quizzes (11) Questions (114)

Questions Related to motion and measurement

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

What is the  $SI$  unit of permeability?

  1. Henry per metre

  2. Tesla metre per ampere

  3. Weber per ampere metre

  4. All the above units are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Permeability (mu) is related to magnetic field intensity H and magnetic flux density B by B = mu*H. The SI unit of B is Tesla (T) and H is Ampere per metre (A/m), so mu = B/H has units of T/(A/m) = T*m/A. Henry per metre (H/m) is also a standard unit, and Weber per ampere metre (Wb/A*m) is equivalent to H/m.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

If E and H represent electric field and magnetic field intensity respectively, then E/H has unit of 

  1. Ampere

  2. Ohm

  3. Volt

  4. Joule
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The ratio of electric field intensity E (V/m) to magnetic field intensity H (A/m) is known as the intrinsic impedance of the medium. The unit is (V/m) / (A/m) = V/A, which is the definition of an Ohm.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Which of the following is not the unit of surface tension ? 

  1. $newton/meter$
  2. $joule/(meter)^2$
  3. $kg/(second)^2$
  4. $watt/ meter$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Surface tension is force per unit length (N/m). Since N = kg*m/s^2, N/m = kg/s^2. Also, surface tension is energy per unit area (J/m^2). Watt/meter is power per unit length, which is not surface tension.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

The Vander waal's equation for gas is given by $\left (P + \dfrac {a}{V^{2}}\right )(V - b) = RT$ where $P$ is pressure, $V$ is volume $'a'$ and $'b'$ are constants, $R$ is universal gas constant and $T$ is absolute temperature. Then the units of $'a'$ are

  1. $dyne\times cm^{5}$
  2. $dyne\times cm^{4}$
  3. $dyne\times cm^{3}$
  4. $dyne\times cm^{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the equation (P + a/V^2)(V - b) = RT, the term a/V^2 must have the same units as pressure P. Thus, units of a = units of P * units of V^2. Pressure is force/area (dyne/cm^2 in CGS) and volume is length^3 (cm^3). So, a = (dyne/cm^2) * (cm^3)^2 = dyne * cm^4.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Acceleration is defined as the rate of change of velocity. Unit of rate of change of acceleration is:

  1. $m/s^{2}$
  2. $m/s^{3}$
  3. $m/s$
  4. $m^{2}/s^{3}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Acceleration has unit $m/{s}^{2}$.

The rate of change of acceleration $\dfrac { d\overset { \rightarrow  }{ a }  }{ dt } =\dfrac { { d }^{ 3 }y }{ d{ t }^{ 3 } } =\dfrac { m }{ { s }^{ 3 } } $
Hence, option B is correct.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

To express all the physical quantities in SI units, we need 

  1. two fundamental units

  2. three fundamental units

  3. five fundamental units

  4. seven fundamental units
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

SI unit system contains seven fundamental quantities which are independent to each other and can be used to represent any given quantity. Hence, all physical quantities can be represented in powers of seven fundamental SI units.

Multiple choice physics motion and measurement physical quantities units - definitions and systems physical quantities like mass and weight

Which of the following quantity is unitless ?

  1. Velocity gradient

  2. Pressure gradient

  3. Displacement gradient

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

Gradient of a quantity $Q$ is given as $\dfrac{\Delta Q}{\Delta x}$
Thus, a gradient will be unitless if its numerator has same dimensions as denominator, i.e. $x$ (which has the dimension $L$).
Thus, out of the options, Displacement has the dimension $L$ and hence its gradient will be dimensionless.