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JEE Main 201511 AprilOnline
Exam
JEE Main
Year
2015
Date
11 April
Mode
Online
Subject
Physics
Chapter
Units and Dimensions

JEE Main 2015 · 11 April · Online · Physics · Units and Dimensions

If electronic charge e , electron mass m , speed of light in vacuum...

If electronic charge ee, electron mass mm, speed of light in vacuum cc and Planck's constant hh are taken as fundamental quantities, the permeability of vacuum μ0{\mu}_{0} can be expressed in units of:

Options

  1. A(mc2he2)\left(\dfrac{m{c}^{2}}{h{e}^{2}}\right)
  2. B(hme2)\left(\dfrac{h}{m{e}^{2}}\right)
  3. C(hcme2)\left(\dfrac{hc}{m{e}^{2}}\right)
  4. D(hce2)\left(\dfrac{h}{c{e}^{2}}\right)

Correct answer

D. (hce2)\left(\dfrac{h}{c{e}^{2}}\right)

Step-by-step solution

Magnetic potential energy inside a solenoid is

U=12LI2U = \dfrac{1}{2}L{I}^{2} Where L=L =self-inductor⇒U=12(μ0n2Al)I2⇒ U = \dfrac{1}{2}\left({\mu}_{0}{n}^{2}Al\right){I}^{2}

∵n=∵ n = number of turns per unit length

=Nl= \dfrac{N}{l}

U=12μ0(Nl)2AlI2U = \dfrac{1}{2}{\mu}_{0}{\left(\dfrac{N}{l}\right)}^{2}Al{I}^{2}

U=12μ0N2l2AlI2U = \dfrac{1}{2}{\mu}_{0}\dfrac{{N}^{2}}{{l}^{2}}Al{I}^{2}

μ0=2UlN2AI2{\mu}_{0} = \dfrac{2Ul}{{N}^{2}A{I}^{2}}

Dimensionally, \left[U\right] = \left[\dfrac{hc}{\lambda}\right]<br/><br/>[I]=[eT]<br /><br />\left[I\right] = \left[\dfrac{e}{T}\right]

\left[A\right] = {\left[l\right]}^{2}<br/><br/>[l]=[l′]<br /><br />\left[l\right] = \left[{l}^{′}\right]

\left[{\mu}_{0}\right] = \left[\dfrac{hc}{\lambda}\right]\dfrac{[ l ]}{\left[{l}^{2}\right]}\dfrac{\left[{t}^{2}\right]}{{\left[e\right]}^{2}}<br/><br/><br /><br />= \left[\dfrac{h}{\lambda}\dfrac{t}{{e}^{2}}\right] = \left[\dfrac{h}{c{e}^{2}}\right]<br/><br/><br /><br />{\mu}_{0} = \dfrac{h}{c{e}^{2}}
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