MCQEasyJEE 2025Dimensions & Dimensional Analysis

JEE Physics 2025 Question with Solution

The dimension of μ0ϵ0\sqrt{\frac{\mu_0}{\epsilon_0}} is equal to that of:

(Where μ0\mu_0 is the vacuum permeability and ϵ0\epsilon_0 is the vacuum permittivity)

  • A

    Voltage

  • B

    Capacitance

  • C

    Inductance

  • D

    Resistance

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: We need the dimension of μ0ϵ0\sqrt{\frac{\mu_0}{\epsilon_0}}, where μ0\mu_0 is vacuum permeability and ϵ0\epsilon_0 is vacuum permittivity.

Find: Which physical quantity has the same dimensions.

From the solution:

  • The dimension of permeability μ0\mu_0 is [MLT2A2][M L T^{-2} A^{-2}].
  • The dimension of permittivity ϵ0\epsilon_0 is [M1L3T4A2][M^{-1} L^{-3} T^{4} A^{2}].

Now evaluate the ratio:

μ0ϵ0=[MLT2A2][M1L3T4A2]=[M2L4T6A4]\frac{\mu_0}{\epsilon_0} = \frac{[M L T^{-2} A^{-2}]}{[M^{-1} L^{-3} T^{4} A^{2}]} = [M^{2} L^{4} T^{-6} A^{-4}]

Step-by-Step Identification

Taking square root,

[M2L4T6A4]=[ML2T3A2]\sqrt{[M^{2} L^{4} T^{-6} A^{-4}]} = [M L^{2} T^{-3} A^{-2}]

This dimensional formula corresponds to inductance.

Therefore, the correct option is C.

Common mistakes

  • Using the incorrect dimensional formula for μ0\mu_0 or ϵ0\epsilon_0. This changes the exponents and gives the wrong physical quantity. Write both formulas carefully before simplifying.

  • Forgetting to divide dimensions properly. When dividing, subtract the exponents of the denominator dimensions from those of the numerator instead of dividing the symbols directly.

  • Not taking the square root of the final dimensional expression. After obtaining the dimension of μ0ϵ0\frac{\mu_0}{\epsilon_0}, halve all exponents to get the dimension of μ0ϵ0\sqrt{\frac{\mu_0}{\epsilon_0}}.

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