Tag: summary of si units

Questions Related to summary of si units

Which of the following systems of units is not based on units of mass, length and time alone ?

  1. SI

  2. MKS

  3. CGS

  4. FPS


Correct Option: A
Explanation:

SI system is based on seven fundamental units. These fundamental units are Kelvin, Second, Kilogram, Metre, Candela, Mole and Ampere.

$1 N = Z  kgf$ (approx.), then what is the value of $Z$?

  1. 0.1

  2. 1

  3. 10

  4. 0


Correct Option: A
Explanation:

The kilogram-force (kgf or kgF) is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a $10\ ms^{-2}$ gravitational field (standard gravity, a conventional value approximating the average magnitude of gravity on Earth).Therefore one kilogram-force is by definition equal to 10 N

So 1 kgf=10N
hence 1N=0.1 kgf  , Z=0.1

What is the C.G.S. unit of force? 

  1. N

  2. N.m

  3. dyne

  4. dyne.cm


Correct Option: C
Explanation:

CGS unit of Force = $dyne$
The dyne is a unit of force specified in the centimetre-gram-second (CGS) system of units, a predecessor of the modern SI. One dyne is equal to $10^{-5}$ N.

What is the ratio of CGS to MKS unit of acceleration?

  1. $\dfrac{m}{cm}$

  2. $\dfrac{m}{s}$

  3. $\dfrac{cm}{s}$

  4. $\dfrac{cm}{m}$


Correct Option: D
Explanation:

CGS unit of acceleration $= cm/s^{2}$
MKS unit of acceleration $=m/s^{2}$
So, ratio of CGS and MKS is $\dfrac{cm}{m}$

The prefix used to represent $\displaystyle { 10 }^{ -2 }$ is called

  1. Milli

  2. Centi

  3. Kilo

  4. Deci


Correct Option: B
Explanation:

The prefix used to represent $10^{-2}$ is called Centi.

1 nano metre (1 nm) is equal to

  1. $\displaystyle { 10 }^{ -7 }$m

  2. $\displaystyle { 10 }^{ -9 }$m

  3. $\displaystyle { 10 }^{ 9 }$m

  4. None of these


Correct Option: B
Explanation:
Nano meter is a very small unit of length.
$1 \ nm = 10^{-9}\  m$

SI unit of energy is joule .

  1. True

  2. False


Correct Option: A
Explanation:

Joule $(J)$ is the SI unit of energy. So, the given statement is true.

The dimensional formula for magnetic flux is:

  1. $(ML^2T^{-2}A^{-1})$

  2. $(ML^3T^{-2}A^{-2})$

  3. $(M^0L^{-2}T^{2}A^{-2})$

  4. $(ML^2T^{-1}A^{2})$


Correct Option: A
Explanation:

The magnetic flux if given by

$\phi=BAcos\theta$
If $cos\theta=1$
The maximum magnetic flux, $\phi=BA$. . . . . .(1)
where, $B=$ magnetic field
$A=area$ 
The dimensional formula for magnetic field,
$F=qvB$
where, $v=$ velocity
$q=$ charge,
$B=$ magnetic field
$[B]=\dfrac{M^1 L^1T^{-2}}{[A^1 T^1][L^1T^{-1}]}$
$[B]=[M^1L^0T^{-2}A^{-1}]$
for area, $[A]=[M^0 L^2 T^0]$
The dimensional formula for magnetic flux,
$[\phi]=[M^1L^0 T^{-2}A^{-1}].[M^0L^2T^0]$
$[\phi]=[M^1L^2T^{-2}A^{-1}]$
The correct option is A.

The SI unit of gravitational potential is :

  1. Joule/kg

  2. Joule$^2$/kg

  3. kg/Joule

  4. Joule/kg$^2 $


Correct Option: A
Explanation:

The gravitational potential at a point is the potential energy associated with a unit mass due to its position in the gravitational field of another body. Gravitational potential is the amount of work done in bringing a body of unit mass from infinity to that point.
Gravitational potential (V) $=\dfrac{Work done}{Mass}=\dfrac{W}{m}$
Gravitational potential  is a scalar quantity and the  SI unit is $J/kg$. 

Siemen is the SI unit of

  1. resistivity

  2. resistance

  3. conductivity

  4. conductance


Correct Option: D
Explanation:

Conductance, $G=\dfrac {1}{resistance}=mho(\Omega^{-1})$ or Siemens (S)


Unit for conductivity is $\mu S/cm$