MCQEasyJEE 2023Dimensions & Dimensional Analysis

JEE Physics 2023 Question with Solution

Match List I with List II:

List I A. Planck's constant hh B. Stopping potential VsV_s C. Work function Φ\Phi D. Momentum pp

List II I. M1L2T2M^1L^2T^{-2} II. M1L1T1M^1L^1T^{-1} III. M1L2T1M^1L^2T^{-1} IV. M1L2T3A1M^1L^2T^{-3}A^{-1}

  • A

    A-III, B-I, C-II, D-IV

  • B

    A-III, B-IV, C-I, D-II

  • C

    A-II, B-IV, C-III, D-I

  • D

    A-I, B-III, C-IV, D-II

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Match physical quantities with their dimensional formulae.

Find: The correct correspondence between List I and List II.

Use the dimensional formula of each quantity:

  • Planck's constant hh has dimensions of energy ×\times time.
[h]=[ML2T2][T]=ML2T1[h] = [ML^2T^{-2}] [T] = ML^2T^{-1}

So, A \rightarrow III.

  • Stopping potential VsV_s has the dimensions of electric potential.
[Vs]=workcharge=ML2T2AT=ML2T3A1[V_s] = \frac{\text{work}}{\text{charge}} = \frac{ML^2T^{-2}}{AT} = ML^2T^{-3}A^{-1}

So, B \rightarrow IV.

  • Work function Φ\Phi is an energy.
[Φ]=ML2T2[\Phi] = ML^2T^{-2}

So, C \rightarrow I.

  • Momentum pp is mass ×\times velocity.
[p]=M×LT1=MLT1[p] = M \times LT^{-1} = MLT^{-1}

So, D \rightarrow II.

Therefore, the correct matching is A-III, B-IV, C-I, D-II. Hence, the correct option is B.

Note: The solution appears unrelated to this question and discusses frequency ranges of communication systems. The answer has therefore been resolved from the dimensional analysis of the given question and the listed options.

Common mistakes

  • Treating Planck's constant hh as energy only. This is wrong because hh comes from E=hνE = h\nu, so it has dimensions of energy multiplied by time. Use [h]=ML2T1[h] = ML^2T^{-1}.

  • Using the dimensions of electric field or energy instead of electric potential for stopping potential VsV_s. Stopping potential is a potential difference, so use work per unit charge: ML2T3A1ML^2T^{-3}A^{-1}.

  • Confusing work function Φ\Phi with momentum because both appear in photoelectric effect questions. Work function is the minimum energy needed to eject an electron, so its dimensions are those of energy: ML2T2ML^2T^{-2}.

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