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Standard form - class-XI

Description: standard form
Number of Questions: 29
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Tags: physics physical world and measurement units and measurement: error analysis dynamics - explaining motion measurements and uncertainties measurements measurement and measuring instrument units and measurement measurements and units physical quantities and measurement nature of the physical world and measurement units and measurements
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Which of the following systems of units is not based on units of mass, length and time alone ?

physics dynamics - explaining motion summary of si units fundamental quantities system of units

  1. SI

  2. MKS

  3. CGS

  4. FPS

Show answer
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 $Z$?

physics dynamics - explaining motion summary of si units fundamental quantities system of units

  1. 0.1

  2. 1

  3. 10

  4. 0

Show answer
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? 

physics dynamics - explaining motion summary of si units fundamental quantities system of units

  1. N

  2. N.m

  3. dyne

  4. dyne.cm

Show answer
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?

physics dynamics - explaining motion summary of si units fundamental quantities system of units

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

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

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

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

Show answer
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

physics dynamics - explaining motion summary of si units fundamental quantities system of units

  1. Milli

  2. Centi

  3. Kilo

  4. Deci

Show answer
Correct Option: B
Explanation:

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

1 nano metre (1 nm) is equal to

physics dynamics - explaining motion summary of si units fundamental quantities system of units

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

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

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

  4. None of these

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

SI unit of energy is joule .

physics dynamics - explaining motion summary of si units fundamental quantities system of units

  1. True

  2. False

Show answer
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:

physics measurements and units summary of si units fundamental quantities system of units

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

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

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

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

Show answer
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 :

physics measurements and units summary of si units fundamental quantities system of units

  1. Joule/kg

  2. Joule$^2$/kg

  3. kg/Joule

  4. Joule/kg$^2 $

Show answer
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

physics measurements and units summary of si units fundamental quantities system of units

  1. resistivity

  2. resistance

  3. conductivity

  4. conductance

Show answer
Correct Option: D
Explanation:

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


Unit for conductivity is $\mu S/cm$

Which of the following unit is not a fundamental unit:

physics measurements and units summary of si units fundamental quantities system of units

  1. Meter

  2. Litre

  3. Second

  4. Kilogram

Show answer
Correct Option: B
Explanation:

Litre is not a fundamental unit.

The SI unit of $ \dfrac{1}{2 \pi \sqrt{LC}}$ is equivalent to that of :

physics measurements and units summary of si units fundamental quantities system of units

  1. time period

  2. frequency

  3. wavelength

  4. wave number

Show answer
Correct Option: B
Explanation:

The angular frequency of current oscillations in an LC circuit is given by $\omega =\dfrac{1}{\sqrt {LC}}$ and $\omega = 2\pi f$.
$\Rightarrow f= \dfrac{1}{2\pi \sqrt{LC}}$ and the unit is equivalent to that of frequency.

The SI unit of coefficient of mutual inductance of a coil is

physics measurements and units summary of si units fundamental quantities system of units

  1. henry

  2. volt

  3. farad

  4. weber

Show answer
Correct Option: A
Explanation:

The henry (symbolized H) is the Standard International ( SI ) unit of coefficient of mutual inductance of a coil .

The S.I. unit of pole strength is

physics measurements and units summary of si units fundamental quantities system of units

  1. $Am^2$

  2. $Am$

  3. $Am^{-1}$

  4. $Am^{-2}$

Show answer
Correct Option: B
Explanation:

Pole strength, $m=\displaystyle \frac {Magnetic \ moment}{2l}=\frac {Am^2}{m}=Am$

Rate of energy dissipation is measured in 

physics measurements and units summary of si units fundamental quantities system of units

  1. Watt

  2. Joule

  3. Weber

  4. Joule / coulomb

Show answer
Correct Option: B

The units of fundamental physical quantities are known as ________ units.

physics measurements and units summary of si units fundamental quantities system of units

  1. Derived

  2. Absolute

  3. Supreme

  4. Fundamental

Show answer
Correct Option: D
Explanation:

The units of fundamental physical quantities are known as fundamental units.

Which of the following does not has fundamental unit?

physics measurements and units summary of si units fundamental quantities system of units

  1. Mass

  2. Time

  3. Force

  4. Electric current

Show answer
Correct Option: C
Explanation:

The fundamental units are defined arbitrarily and they are used to derive of others unit. Generally the most common fundamental units are mass, time, length and current.

As the unit of force can be derived from three fundamental units, mass, length and time so the force does not has fundamental unit.

Light year is a measurement of 

physics measurements and units summary of si units fundamental quantities system of units

  1. Speed of aeroplanes

  2. Speed of light

  3. Stellar distances

  4. Speed of rockets

Show answer
Correct Option: C
Explanation:

Light year is the unit of astronomical distance. It is a distance that light travels in one year. 

So, $1$ light year $=(3\times 10^8)\times (365\times 24\times 3600)=9.46\times 10^{15} m$

Write S.I. unit of charge

physics measurements and units summary of si units fundamental quantities system of units

  1. C

  2. A

  3. N m$^2$

  4. None of the above

Show answer
Correct Option: A
Explanation:

SI unit of charge is Coulomb which is represented by the symbol $C$.

The quantity represented by the product of "Resistance and inductance" is

physics measurements and units summary of si units fundamental quantities system of units

  1. mass

  2. length

  3. time

  4. none

Show answer
Correct Option: D
Explanation:

The product of resistance and inductance is not represented by any quantity given above.

SI unit of moment of couple is ____.

physics measurements and units summary of si units fundamental quantities system of units

  1. $N m$

  2. $dyne \ cm$


  3. $N m^{-2}$

  4. none of the above

Show answer
Correct Option: A
Explanation:
Moment of couple is torque which is equal to the product of force applied to the distance.
Moment of couple   $\tau = rF$
SI unit of moment of couple is $Nm$

The dimensions of ratio of magnetic flux $(\phi)$ and permeability $(u)$ are:

physics measurements and units summary of si units fundamental quantities system of units

  1. $[M^0 L^1 A^1 T^0]$

  2. $[M^0 L^{-3} T^0 A^1]$

  3. $[M^0 L^{-1} T^1 A^{-1}]$

  4. $[M^0 L^2 T^0 A^1]$

Show answer
Correct Option: A
Explanation:

Magnetic flux $= B.A.$
Permatibility $= \dfrac{B}{H} = \dfrac{J}{A.M}$

$= \dfrac{BA}{B/H}$

$= \dfrac{BAH}{B} = AH$

$= [L^2] [AC^{-1}]$

$= [M^o LAT^o]$

The solid angle subtended at any point inside the surface due to small area ds is given by 

physics measurements and units summary of si units fundamental quantities system of units

  1. $r^2ds \cos \theta$

  2. $\dfrac{ds \cos \theta }{r^2}$

  3. $\dfrac{ds\cos \theta }{r}$

  4. $\dfrac{r^2}{ds \cos \theta}$

Show answer
Correct Option: B
Explanation:

The solid angle $\Omega=\dfrac{A}{r^2}$

where, $A=$ area
When solid angle subtended at any point inside the surface due to small area $ds$
$A=ds$ $cos\theta$
Solid angle $\Omega=\dfrac{dscos\theta}{r^2}$
The correct option is B.

Unit of density and relative density are same.

physics measurements and units summary of si units fundamental quantities system of units

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Unit of density is $g/cm^3$ whereas relative density is unitless. Thus the given statement is false.

Hertz is the unit of

physics measurements and units summary of si units fundamental quantities system of units

  1. wavelength

  2. amplitude

  3. frequency

  4. None of these

Show answer
Correct Option: C
Explanation:

Hertz is the fundamental unit of frequency.

The SI unit of electron mobility is  :

physics measurements and units summary of si units fundamental quantities system of units

  1. ${M^2}{S^{ - 1}}V - 1$

  2. $=m^2 s^{-1}V^{-1}$

  3. $m{s^{ - 1}}V$

  4. ${m^2}{s^{ - 2}}V$

Show answer
Correct Option: B
Explanation:

Electron mobility:- It is the ratio of velocity to electric field.

$\mu=\dfrac{v _e}{E}$. . . . . . .(1)
SI unit of velocity, $v _e$ $=m/s$
SI unit of electric field, $E$ $=V/m$
From equation (1),
SI unit of electron mobility is $=\dfrac{m/s}{V/m}$
$=m^2/Vs$
$=m^2 s^{-1}V^{-1}$

The dimensional formula of a physical quantity is $\displaystyle { M }^{ 1 }{ L }^{ 2 }{ T }^{ 3 }{ I }^{ -1 }$ .What is its SI unit?

physics measurements and units summary of si units fundamental quantities system of units

  1. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 3 }{ A }^{ -1 }$

  2. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 2 }{ A }$

  3. $\displaystyle { kg\quad ms }^{ -3 }{ A }^{ 2 }$

  4. $\displaystyle { kg}^{2}{ m }^{ 2 }{ s }^{ 3}{ A }^{ -1 }$

Show answer
Correct Option: A
Explanation:

SI unit of $M$ is $kg$, that of $L$ is $m$, $T$ is $s$ and $I$ is $A$.
So, SI unit of $[M^1L^2T^{3}I^{-1}]$ is  $kg \ m^2s^{3}A^{-1}$.

Find the unit of the following derived quantities: 
(a) Force [Hint: Force = Mass $\times$ acceleration]
(b) Pressure $\left[Hint: Pressure =\frac{force}{Area}\right]$

physics measurements and units summary of si units fundamental quantities system of units

  1. $kg\,m\,s^{-2}$ and $kg\,m^{-1}\,s^{-2}$

  2. $kg\,m\,s^{-1}$ and $Kg\,m^{-2}\,s^{-1}$

  3.  $ N$ and $ Pa$

  4. None of these

Show answer
Correct Option: A,C
Explanation:
Force   $F = ma$
So, unit of force is  $kg \ m/s^2$
Newton $(N)$ is also the unit of force.
Pressure   $P = \dfrac{F}{A}$
Unit of pressure   $ = \dfrac{kg \ m/s^2}{m^2} = kg \ m^{-1}s^{-2}$
Also, pressure is measured in Pascal $(Pa)$.

The S.I. unit of magnetic pole strength is_______

physics measurements and units summary of si units fundamental quantities system of units

  1. $A.{ m }^{ 2 }$

  2. $A.{ m }^{ -1 }$

  3. A.m

  4. $A/{ m }^{ 2 }$

Show answer
Correct Option: C
Explanation:

Magnetic pole strength is the strength of a magnetic pole to attract magnetic materials towards itself . S.I. unit of magnetic pole strength is Ampere-meter $(A\,m)$.

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