Physics · Science General

Units and Measurement

1,044 Questions

Master the fundamentals of physics with these practice questions on units and measurement. The topics include fundamental SI units, derived quantities, and specific units for power, force, and light. These questions are essential for building a strong foundation for competitive exams.

SI fundamental unitsUnits of powerDerived quantities unitsThermal energy unitsVolume measurement unitsElectric current units

Units and Measurement Questions

Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

If the values of force and length are increased four times, then the unit of energy will be increase by:

  1. 4 times

  2. 2 times

  3. 8 times

  4. 16 times
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The correct option is D
We have, $f=4[MLT^{-2}]$ and $d=4[L]$

$E=f\times d$

We know that Energy is equal to the product of force and distance.

Thus,
$=4[MLT^{-2}]\times4[L]$

$=16[ML^2T^{-2}]$

If both increased by 4times then the energy increased by $16\ times$
Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

If unit of mass, length and time are tripled, then unit of energy becomes:

  1. $3$
  2. $\dfrac{1}{3}$
  3. $9$
  4. $\dfrac{1}{9}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Unit of Energy $kg\,m^2/s^2$

Unit of length $= m$ (metre)

Unit of mass $= kg$ (kilogram)

Unit of time $= s$ (second)


Thus unit of energy in terms of unit of mass, length and time is given by,

$Unit \,of\, Energy =\dfrac{(Unit\,of\,mass)\times(Unit\,of\,length)^2}{(Unit\,of\,time)^2}$

If the unit of mass, length and time are tripled the unit of energy will be,

$Unit \,of\, Energy =\dfrac{(3\times Unit\,of\,mass)\times(3\times Unit\,of\,length)^2}{(3\times Unit\,of\,time)^2}$

$Unit \,of\, Energy =3\times \dfrac{(Unit\,of\,mass)\times(Unit\,of\,length)^2}{(Unit\,of\,time)^2}$

$Unit\,of\,energy=3\times Unit\,of\,energy$

Therefore, if the unit of mass, length and time are tripled, the unit of energy will be, 3 times more than the original unit of energy.
Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

$\displaystyle kg{ ms }^{ -1 }$ is the SI unit of

  1. Impulse

  2. Force

  3. Angular velocity

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Impulse $(I)$ imparted to the body is equal to the change in linear momentum $(\Delta p)$ of the body.


Impulse, $I=\Delta p$

Thus momentum has the same units as that of impulse. Since momentum has S.I. unit as $kgms^{-1}$, impulse also has S.I. unit as $kgms^{-1}$.

Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

SI unit of Magnetic flux is weber and its CGS unit is maxwell. Then 1 Wb = :

  1. $10^6$ maxwell
  2. $10^7$ maxwell
  3. $10^8$ maxwell
  4. $10^9$ maxwell
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Magnetic flux is the product of magnetic field and area.

As SI unit of magnetic flux is weber, so $1 \, Wb=Tesla (T)\times m^2$
where $1 \, T=10^{4} \, gauss$ and $1 m^2=10^4 cm^2$
(T and gauss is the SI and CGS unit of magnetic field )
So, $1 \, Wb=10^4 \, gauss \times 10^4cm^2=10^8 $ maxwell

Multiple choice physics dynamics - explaining motion system of unit summary of si units system of units

$S = A(1 - e^{-Bxt})$, where S is speed and x is displacement. The unit of B is :

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

It is given that $x$ is displacement and $t$ is time.
Unit of $x$ is $m$ and that of time t is $s$.
Since, the quantity $Bxt$ must be dimensionless.
$\implies$ Unit of B must be $m^{-1}s^{-1}$.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation density of a fluid density of fluid density and relative density

The unit of density in MKS and CGS system respectively are:

  1. $\displaystyle { kg }/{ { m }^{ 3 } }and\quad { g }/{ { cm }^{ 3 } }$
  2. $\displaystyle { g }/{ { cm }^{ 3 } }and\quad { kg }/{ { m }^{ 3 } }$
  3. $\displaystyle { g }/{ { cm }^{ 2 } }and\quad { kg }/{ { m }^{ 2 } }$
  4. $\displaystyle { kg }/{ { cm }^{ 2 } }and\quad { g }/{ { m }^{ 2 } }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Density is defined as the mass per unit volume of a substance. 

Density = $\cfrac{mass}{volume}$. 
In MKS system i.e. the SI system the unit of density is $\displaystyle { kg }/{ { m }^{ 3 } }$ and CGS system it is $\displaystyle { g }/{ { cm }^{ 3 } }$.

Multiple choice physics dynamics - explaining motion exponentiation index notation and products of prime factors powers

The wrong unit conversion among the following is

  1. 1 angstrom = $10^{-10} m$
  2. 1 fermi = $10^{-15}$ m
  3. 1 light year = $9.46 \times 10^{15} m$
  4. 1 astronomical unit = $1.496 \times 10^{-11} m$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
$A)1 $Angstrom: $1$ Ångström is equal to$ 0.1 $nanometers. Expressed in the SI base unit meters $1$ Ångström is equal to $1 \times 10^{-10}$ meters. $1 Å = 0.0000000001 m.$

$B)$Definition of fermi unit: $≡ 1\times 10^{−15} m.$

$C)$The light-year is a unit of length used to express astronomical distances and measures about $9.46$ trillion kilometres $(9.46 \times 10^{12} km)$ or $5.88$ trillion miles $(5.88 \times 10^{12} mi).$

$D)$The total radiation power received from the sun on a unit area perpendicular to the sun rays at the mean earth-sun distance, termed an astronomical unit, is called the solar constant (SC), where $1$ astronomical unit $= 1 AU = 1.496 \times 10^{11} m.$

So $D$ is wrong unit conversion 

Multiple choice physics dynamics - explaining motion exponentiation index notation and products of prime factors powers

A calorie is a unit of heat energy and its value is 4.18 J where $1 J = 1 kg m^2 s^{-2}$. Suppose we use a new system of units in which unit of mass equals $\alpha$ kg, the unit of length equals $\beta$ m and the unit of the time is $\gamma$ sec. Then the value of a calorie in the new system of units is then

  1. 4.18 $\displaystyle \frac{\gamma^2}{\alpha \beta^2}$
  2. 4.18 $\displaystyle \frac{\alpha \beta^2}{\gamma^2}$
  3. 4.18 $\displaystyle \frac{\gamma^2}{\alpha}$
  4. 4.18 $\displaystyle \frac{\beta^2}{\alpha \gamma^2}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$1 J = (1 kg) ( 1 m)^2 (1 sec)^{-2}$
$1 x = (\alpha kg) (\beta m)^2 (\gamma sec)^{-2}$
$\displaystyle \therefore \frac{1 J}{1x} = \left( \frac{1}{\alpha} \right) \left( \frac{1}{\beta} \right)^2 (\gamma)^2 = \frac{\gamma^2}{\alpha \beta^2} $
$\displaystyle \therefore 1 J = \frac{\gamma^2}{\alpha \beta^2}$ or $\displaystyle 1 cal = 4.18 \displaystyle \frac{\gamma^2}{\alpha \beta^2}$

Multiple choice physics dynamics - explaining motion exponentiation index notation and products of prime factors powers

Electron volt is the unit used to represent 

  1. energy

  2. power

  3. intensity

  4. charge of electron.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electron volt, unit of energy commonly used in atomic and nuclear physics, equal to the energy gained by an electron (a charged particle carrying unit electronic charge) when the electrical potential at the electron increases by one volt. The electron volt equals $1.602\times 10^{-12}\,erg$  or  $1.602\times 10^{-19}\,joule$.