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 energy and its forms idea of energy introduction to work and energy work and energy

Name the quantity which is measured in $Wh$.

  1. Force

  2. Power

  3. Energy

  4. All the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

We know that $ power = work/ time$.

Power has unit $W$ and time can have either seconds or minutes or hours.Hence work can have either $W\ min$ or $Wh$ or $Ws$. We in general consider work is nothing but energy. Hence energy can have unit $Wh$.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

Which of the following is the biggest unit of energy?

  1. Joule

  2. Kilowatt hour

  3. Erg

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

Since, we know that SI unit of energy is represented by Joule. Hence, let us convert all the different units in the form of Joules. 


Option A- 
1 Joule= $1\quad Joule\quad =\quad [kg]{ [\frac { m }{ s } ] }^{ 2 }$

Option B-
$kWh\quad =\quad 1000W\times 3600s\quad =\quad 3600000\quad W\times s$

As we know that 1 Ws = 1 Joule

So 1 kWh= 3600000 Joules

Option C- 
$1\quad Joule\quad =\quad [kg]{ [\frac { m }{ s } ] }^{ 2 }=\quad \left[ 1000\quad gm \right] \left[ \frac { 100\quad cm }{ 1\quad s }  \right] \left[ \frac { 100\quad cm }{ 1\quad s }  \right] \ S0,\quad 1\quad Joule\quad =\quad { 10 }^{ 7 }gm\frac { { cm }^{ 2 } }{ { s }^{ 2 } } \quad =\quad { 10 }^{ 7 }\quad erg\ So,\quad 1\quad erg\quad =\quad { 10 }^{ -7 }Joule$

Option D- 
Electron Volt is the unit of energy in terms of change in energy for one electron in the potential difference of one volt. So, mathematically it is-

$1\quad ev\quad =\quad Charge\quad of\quad one\quad electron\quad \times \quad 1\quad Volt\quad =\quad 1.6\quad \times { 10 }^{ -19 }Coloumb\quad \times \quad 1\frac { Joule }{ Coloumb } \ So,\quad 1\quad ev=\quad =\quad 1.6\quad \times { 10 }^{ -19 }Joule$

Hence, Option B is the largest unit of energy and hence it is practically used in everyday life of electric consumption. 

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

The ratio of SI units to CGS units of energy is

  1. 10$^5$
  2. 10$^6$
  3. 10$^7$
  4. 10$^{-7}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Unit of energy is $ML^2T^{-2}$ 

So in  $CGS$ unit, mass = gram, length = centimeter, time = second.
And in $SI$ unit, mass = kilo gram, length = meter ,time = second.
So ratio of both SI to CGS

=$\dfrac{kg.m^2.s^{-2}  }{g.cm^2.s^{-2}}$

=$\dfrac {1000g.100^2cm^2.s^{-2}}{g.cm^2s^{-2}}$

=$10^7$.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

Kilowatt hour (kWh) represents the unit of____

  1. power

  2. impulse

  3. mementum

  4. none of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The kilowatt hour is a unit of energy equal to $3.6\times 10^6J$. If the energy is being transmitted or used at a constant rate (power) over a period of time, the total energy in kilowatt hours is the power in kilowatts multiplied by the time in hours. so if kWh is unit of energy so none of the option is correct hence option D is the answer.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

The unit of work is joule $(J)$ in the $SI$ system and erg in the $CGS$ system. Find number of ergs in $1\ joule$.

  1. $10^{17} ergs$.
  2. $10^{9} ergs$.
  3. $10^{8} ergs$.
  4. $10^{7} ergs$.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In the SI system, 1 Joule = 1 kg * m^2 / s^2. In the CGS system, 1 erg = 1 g * cm^2 / s^2. Since 1 kg = 10^3 g and 1 m^2 = 10^4 cm^2, 1 J = 10^3 * 10^4 = 10^7 ergs.