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NEET 2015
Exam
NEET
Year
2015
Subject
Physics
Chapter
Units and Dimensions

NEET 2015 · Physics · Units and Dimensions

If dimensions of critical velocity, v _ c of a liquid flowing...

If dimensions of critical velocity, vc{v}_{c} of a liquid flowing through a tube are expressed as \left[{η}^{x}{ρ}^{y}r^{z}\right],where, , where,~η, ρ and rarethecoefficientofviscosityofliquid,densityofliquidandradiusofthetube,respectively,then,thevaluesofare the coefficient of viscosity of liquid, density of liquid and radius of the tube, respectively, then, the values ofx,yand, y and\text{z}$ are given by

Options

  1. A−1,−1,1- 1, - 1, 1
  2. B−1,−1,−1- 1, - 1, - 1
  3. C1,1,11, 1, 1
  4. D1,−1,−11, - 1, - 1

Correct answer

D. 1,−1,−11, - 1, - 1

Step-by-step solution

Dimensions of velocity, coefficient of viscosity and density are,

[v]=[LT−1]\left[v\right] = \left[{LT}^{- 1}\right]

\left[η\right] = \dfrac{\left[F\right]}{\left[A\dfrac{d v}{d x}\right]} = \dfrac{\left[{MLT}^{- 2}\right]}{\left[{L}^{2}\right]\left[{T}^{- 1}\right]} = \left[{ML}^{- 1}{T}^{- 1}\right]</p></blockquote><blockquote><p>[ρ]=[ML−3]</p></blockquote><blockquote><p>\left[ρ\right] = \left[{ML}^{- 3}\right]

Now, \left[v\right] = {\left[η\right]}^{x}{\left[ρ\right]}^{y}{\left[r\right]}^{z}</p><p></p><p>⇒ \left[{LT}^{- 1}\right] = {\left[{ML}^{- 1}{T}^{- 1}\right]}^{x}{\left[{ML}^{- 3}\right]}^{y}{\left[L\right]}^{z}</p><p>Now,byusingdimensionalhomogeneity,wewillget,</p><p></p><p>Now, by using dimensional homogeneity, we will get,</p><p>{M}^{0} = {M}^{\left(x + y\right)}</p><p></p><p>⇒ y = - x</p><p>For</p><p>ForT,</p><p>, </p><p>x = 1</p><p></p><p>⇒ y =- x =- 1</p><p>For</p><p>ForL,</p><p>,</p><p>1 = - x - 3y + z</p><p></p><p>⇒ z = - 1

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