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NEET
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NEET
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Physics
Chapter
Units and Dimensions

NEET · Physics · Units and Dimensions

Match List-I with List-II. List-I List-II (A) Planck Length (I) c^...

Match List-I with List-II.

List-IList-II
(A) Planck Length(I) c1/2G−1/2h1/2c^{1/2} G^{-1/2} h^{1/2}
(B) Planck Mass(II) c−3/2G1/2h1/2c^{-3/2} G^{1/2} h^{1/2}
(C) Planck Time(III) c5/2G−1/2h1/2c^{5/2} G^{-1/2} h^{1/2}
(D) Planck Energy(IV) c−5/2G1/2h1/2c^{-5/2} G^{1/2} h^{1/2}

Choose the correct answer from the options given below:

Options

  1. A(A)-(IV), (B)-(I), (C)-(II), (D)-(III)
  2. B(A)-(II), (B)-(III), (C)-(IV), (D)-(I)
  3. C(A)-(II), (B)-(I), (C)-(IV), (D)-(III)
  4. D(A)-(I), (B)-(II), (C)-(III), (D)-(IV)

Correct answer

C. (A)-(II), (B)-(I), (C)-(IV), (D)-(III)

Step-by-step solution

First, write the dimensional formulas for the fundamental constants:
Speed of light, [c]=[LT−1][c] = [L T^{-1}]
Universal gravitational constant, [G]=[M−1L3T−2][G] = [M^{-1} L^3 T^{-2}]
Planck's constant, [h]=[ML2T−1][h] = [M L^2 T^{-1}]

Let us evaluate the common term G1/2h1/2G^{1/2} h^{1/2}:
[Gh]1/2=(M−1L3T−2×ML2T−1)1/2=(L5T−3)1/2=[L5/2T−3/2][G h]^{1/2} = (M^{-1} L^3 T^{-2} \times M L^2 T^{-1})^{1/2} = (L^5 T^{-3})^{1/2} = [L^{5/2} T^{-3/2}]

To obtain Planck Length [L1][L^1], we need to multiply by a power of cc that yields L1T0L^1 T^0.
Multiplying by c−3/2=(LT−1)−3/2=L−3/2T3/2c^{-3/2} = (L T^{-1})^{-3/2} = L^{-3/2} T^{3/2} gives:
L5/2T−3/2×L−3/2T3/2=[L1]L^{5/2} T^{-3/2} \times L^{-3/2} T^{3/2} = [L^1].
Thus, Planck Length ∝c−3/2G1/2h1/2\propto c^{-3/2} G^{1/2} h^{1/2}. (A →\rightarrow II)

To obtain Planck Time [T1][T^1], multiply by c−5/2=L−5/2T5/2c^{-5/2} = L^{-5/2} T^{5/2}:
L5/2T−3/2×L−5/2T5/2=[T1]L^{5/2} T^{-3/2} \times L^{-5/2} T^{5/2} = [T^1].
Thus, Planck Time ∝c−5/2G1/2h1/2\propto c^{-5/2} G^{1/2} h^{1/2}. (C →\rightarrow IV)

Now evaluate the term G−1/2h1/2G^{-1/2} h^{1/2}:
[G−1h]1/2=(ML−3T2×ML2T−1)1/2=(M2L−1T1)1/2=[M1L−1/2T1/2][G^{-1} h]^{1/2} = (M L^{-3} T^2 \times M L^2 T^{-1})^{1/2} = (M^2 L^{-1} T^1)^{1/2} = [M^1 L^{-1/2} T^{1/2}]

To obtain Planck Mass [M1][M^1], multiply by c1/2=L1/2T−1/2c^{1/2} = L^{1/2} T^{-1/2}:
M1L−1/2T1/2×L1/2T−1/2=[M1]M^1 L^{-1/2} T^{1/2} \times L^{1/2} T^{-1/2} = [M^1].
Thus, Planck Mass ∝c1/2G−1/2h1/2\propto c^{1/2} G^{-1/2} h^{1/2}. (B →\rightarrow I)

To obtain Planck Energy [ML2T−2][M L^2 T^{-2}], multiply by c5/2=L5/2T−5/2c^{5/2} = L^{5/2} T^{-5/2}:
M1L−1/2T1/2×L5/2T−5/2=[ML2T−2]M^1 L^{-1/2} T^{1/2} \times L^{5/2} T^{-5/2} = [M L^2 T^{-2}].
Thus, Planck Energy ∝c5/2G−1/2h1/2\propto c^{5/2} G^{-1/2} h^{1/2}. (D →\rightarrow III)

The correct matching is (A)-(II), (B)-(I), (C)-(IV), (D)-(III).

Answer: (A)-(II), (B)-(I), (C)-(IV), (D)-(III)
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