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JEE Main 2020 (5 Sep, Shift 2) · Units & Dimensions

Units & Dimensions question from JEE Main 2020 (5 Sep, Shift 2)

Q74JEE Main 2020 · 5 SEP · SHIFT 2Medium

Units & Dimensions

The quantities x = 1μ0ε0\frac{1}{\sqrt{\mu_0\varepsilon_0}}, y = EB\frac{E}{B} and z = lCR\frac{l}{CR} are

defined where C-capacitance, R-Resistance, l-length, E-Electric field, B-magnetic field and ε0,μ0\varepsilon_0, \mu_0, - free space permittivity and permeability respectively. Then:

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Answer: (b)

  1. x=1μ0ε0=cx = \dfrac{1}{\sqrt{\mu_0\varepsilon_0}} = c, a speed [LT−1][\mathrm{LT^{-1}}].
  2. From F=qE=qvBF = qE = qvB, EB=v\dfrac{E}{B} = v, so y=[LT−1]y = [\mathrm{LT^{-1}}].
  3. CRCR is a time constant [T][\mathrm{T}], so z=lCR=[LT−1]z = \dfrac{l}{CR} = [\mathrm{LT^{-1}}].
  4. So the answer is (b) x, y and z have the same dimension.
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