Tag: measurements and units

Questions Related to measurements and units

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

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

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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 $(A\,m)$.

There are $n\ sets$ of real numbers. In every set there are four real numbers in AP. Such that the square of the last term is equal to the sum of the square of the first three terms. Then: -

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $N = 4$

  2. $N = 1000$

  3. $N = 10$

  4. $N \rightarrow \infty$

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Correct Option: C

Four  positive charges $ ( 2 \sqrt 2-1 )Q $ are arranged at corner of square . another charge q is placed at the centre of the square. resultant force acting on each corner is zero if q is :

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $-7Q/4$

  2. $-4Q/ 7$

  3. $-Q$

  4. $none$

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Correct Option: C

A public park, in the form of a square, has an area of $(100 \pm 0.2 )m^2 $ .The side of park is :

physics measurements and units measurement of area and volume measurement of volume measurement of area, volume and density

  1. $ (10 \pm 0.01 ) m $

  2. $ (10 \pm 0.1 ) m $

  3. $ (10 \pm 0.02 ) m $

  4. $ (10 \pm 0.2 ) m $

Show answer
Correct Option: A
Explanation:

Let the side length of the square park is $l$.

The area of a square is given as,

$A = {l^2}$

$100 = {l^2}$

$l = 10\;{\rm{m}}$

The error in length is given as,

$\dfrac{{\Delta A}}{A} = 2\dfrac{{\Delta l}}{l}$

$\dfrac{{0.2}}{{100}} = 2\dfrac{{\Delta l}}{{10}}$

$\Delta l = 0.01\;{\rm{m}}$

Thus, the side of the park is $\left( {10 \pm 0.01} \right)\;{\rm{m}}$.

Which of the following is not the name of a physical quantity?

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

  1. Time

  2. Impulse

  3. Mass

  4. Kilogram

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Correct Option: D
Explanation:

The kilogram represents the unit of a physical quantity and not the physical quantity

In International System of units, there are seven base quantities whose units are defined. Which physical quantity has a prefix with its unit?

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

  1. Mass

  2. Thermodynamic temperature

  3. Luminous intensity

  4. Amount of substance

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Correct Option: A
Explanation:

Unit of mass is kilogram and here, kilo is a prefix used in the unit. Thus mass is the physical quantity which has prefix with its unit.

The Richardson equation is given by $I = AT^2 e^{-B/kT}$. The dimensional formula for $AB^2$ is same as that for

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

  1. $IT^2$

  2. $kT$

  3. $Ik^2$

  4. $Ik^2/ T$

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Correct Option: C
Explanation:

$I = AT^2 e^{-B/kT}$
Dimensionally, $A = I/T^2$, dimensions of B = kT
($\because$ power of exponential is a number)
$\displaystyle AB^2 = \frac{I}{T^2} (kT)^2 = Ik^2$

The SI unit of temperature is Kelvin.

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

  1. True

  2. False

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Correct Option: A
Explanation:
S.I. unit of temperature is Kelvin represented by $K$.
Hence the above statement is true.

S.I. unit of frequency is _______.

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

  1. Hertz

  2. Candela

  3. Newton

  4. Dyne

Show answer
Correct Option: A
Explanation:
Frequency is defined as the number of revolutions completed by the object in one second.
S.I. unit of frequency is Hertz denoted by $Hz$.