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JEE Main 202226 JuneMorning Shift
Exam
JEE Main
Year
2022
Date
26 June
Shift
Morning Shift
Subject
Physics
Chapter
Units and Dimensions

JEE Main 2022 · 26 June · Morning Shift · Physics · Units and Dimensions

An expression for a dimensionless quantity P is given by P =...

An expression for a dimensionless quantity PP is given by P=αβlog⁡e(kT\betax)P = \dfrac{\alpha}{\beta}\log_{e}\left(\dfrac{kT}{\betax}\right); where α\alpha and β\beta are constants, xx is distance; kk is Boltzmann constant and TT is the temperature. Then the dimensions of α\alpha will be

Options

  1. A[M0L−1T0]\left[{M}^{0}{L}^{- 1}{T}^{0}\right]
  2. B[ML0T−2]\left[{ML}^{0}{T}^{- 2}\right]
  3. C[MLT−2]\left[{MLT}^{- 2}\right]
  4. D[ML2T−2]\left[{ML}^{2}{T}^{- 2}\right]

Correct answer

C. [MLT−2]\left[{MLT}^{- 2}\right]

Step-by-step solution

Given p=αβln⁡(kT\betax)p = \dfrac{\alpha}{\beta}\ln \left(\dfrac{kT}{\betax}\right)

We know that expression inside log is dimensionless.

Therefore,\left[\dfrac{kT}{\betax}\right]isdimensionless</p><p>is dimensionless</p><p>⇒ \left[\beta\right] = \left[\dfrac{kT}{x}\right] = {ML}^{2}{T}^{- 2}{K}^{- 1} \times K \times {L}^{- 1} = {MLT}^{- 2}</p><p>Since</p><p>Sincepisdimensionlessis dimensionless∴ \left[p\right] = [αβ]=M0L0T0\left[\dfrac{\alpha}{\beta}\right] = {M}^{0}{L}^{0}{T}^{0} ⇒[α]=[β]⇒ \left[\alpha\right] = \left[\beta\right] ⇒[α]=MLT−2⇒ \left[\alpha\right] = {MLT}^{- 2}

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