Physics · Science General

Units and Measurement

998 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

$\displaystyle kg{ ms }^{ -1 }$ 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  $1.602\times 10^{-19}\,joule$.

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

If the units of length and force are increased four times, then unit of energy will

  1. becomes 8 times

  2. becomes 16 times

  3. decrease 16 times

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

Unit of Energy $= kg. m^2/ s^2$

Unit of Force $= kg. m/s^2$

Unit of Length $= m$

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

Unit of Energy $= (kg. m/s^2) \times (m)$

If the units of length and force are increased by four times,

the unit of energy will be:

Unit of Energy $= (4 .kg. m/s^2) \times (4m)$

Unit of Energy $= 16 (kg. m^2/s^2)$

Therefore, if the units of length and force are increased by four times, the unit of energy will change by $16$ times.

Multiple choice physics work and energy commercial unit of energy power work and power

Choose the correct option.

  1. kW$=$ unit of power and kWh $=$ unit of energy.
  2. kW$=$ unit of energy and kWh $=$ unit of power.

  3. kW and kWh are both of unit of energy.

  4. kW and kWh are both of unit of power.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electrical Power is measured in watts (W), kilo-watts (kW), mega-watts (MW), and giga-watts (GW). The power of a load can change quickly, especially if the load is turning on and off.

Electrical Energy is measured in kilowatt-hours (kWh), megawatt-hours, and sometimes (less commonly) in watt-hours or watt-seconds. Energy is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.

Multiple choice physics work and energy commercial unit of energy power work and power

Which of the following can be used to express energy? Symbols have their usual meanings for the units of physical quantities.
(i) Wh   (ii) VC    (iii) VAs$^2$  (iv)  A$^2\Omega$s

  1. (i) , (ii)

  2. (ii), (iii), (iv)

  3. (i), (ii), (iv)

  4. (i), (ii), (iii), (iv)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using   $E = Pt$       $\implies$ Energy can be expressed in $Wh$

Using  $W = qV$     $\implies$ Energy can be expressed in $VC$
Using  $H = i^2Rt$  $\implies$ Energy can be expressed in $A^2\Omega s$
Whereas  Energy cannot be expressed by  $VAs^2$
Hence option C is correct.

Multiple choice physics work and energy commercial unit of energy power work and power

Smallest commercial unit of energy is

  1. Kilowatt hour

  2. Watt second

  3. Watt hour

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

Smallest commercial unit of energy is called Watt hour. It is defined as the amount of electric energy, which flows through a conductor in one hour, at a power of one watt.

Multiple choice physics work and energy commercial unit of energy power work and power

Kilowatt-hour is the unit of :

  1. potential difference.

  2. electric power.

  3. electrical energy.

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

The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour. The kilowatt-hour is commercially used as a billing unit for energy delivered to consumers by electric utilities.