Tag: fundamental and derived units

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Multiple choice physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

Identify the uncommon quantity

Weight, spring balance, newton, kilogram 

  1. kilogram

  2. Weight

  3. spring balance

  4. newton
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The spring balance is the device used for measurement of weight. The weight of a body is measured in terms of the newton. On the other hand, kilogram is the unit for the mass of the body.


Therefore, spring balance, weight and Newton are related to the same thing i.e.the weight of a body whereas the kilogram is related to the mass of the body. So, kilogram is different.

Multiple choice physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

Identify the common unit used to measure energy?

  1. Newtons

  2. Joules

  3. Grams

  4. Meters

  5. Liters
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Newton is the unit of force.

Joules is the SI unit of energy. It is equivalent to newton-meter($N-m$).
Grams is a unit of mass.
Meter is the SI unit of distance.
A liter is a unit of volume and equivalent to $dm^3$.

Therefore option $B$ is correct.

Multiple choice physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

Identify the derived quantities among the following.

  1. Gravitational constant

  2. Frequency

  3. Electric charge

  4. Electric current
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

The derived quantities are the one which depends on the other fundamental quantities for their representation. Among the following quantities, an electric current is a fundamental quantity whereas gravitational constant, frequency and electric charge are the derived quantities.

Multiple choice physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

Using dimensional analysis the resistivity in terms of fundamental constants $h, m _e, c, e, \varepsilon _o$ can be expressed as.

  1. $\displaystyle\frac{h}{\varepsilon _0m _ece^2}$
  2. $\displaystyle\frac{\varepsilon _0m _ece^2}{h}$
  3. $\displaystyle\frac{h^2}{m _ece^2}$
  4. $\displaystyle\frac{m _e\varepsilon _0}{ce^2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

 SI base units of resistivity are written as $Kgm^3s^{-1}C^{-2}$.

For plank constant  $h$  SI base units are $Kgm^2s^{-1}$.
For $e$  SI unit is $C$.
For $c$  SI unit is $ms^{-1}$.
For $m _e$ SI unit is $Kg$.
For $\varepsilon _o$ SI unit is $C^2{Kg}^{-1}m^{-3}s^{2}$
Solving the dimensions of constants in option $C$,
$\dfrac{({Kgm^2s^{-1}})^2}{Kgms^{-1}C^2}=Kgm^3s^{-1}C^{-2}$
We get the dimensions of resistivity hence option $C$ is correct.

Multiple choice physics measurements and units some examples of derived units fundamental and derived quantities fundamental and derived units

Which of the following quantities has its unit as newton second?

  1. Energy

  2. Torque

  3. Momentum

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

Dimensional formula of newton second $=\left[ \dfrac { kgm }{ { S }^{ 2 } } \times S \right] $

$=\left[ { MLT }^{ -1 } \right] $
Dimensional formula of momentum $=\left[ { MLT }^{ -1 } \right] $
Hence, momentum has the unit as $Nsec$.