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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Introduction to Physics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Introduction to Physics

Determine if the following equation is dimensionally correct: V =...

Determine if the following equation is dimensionally correct:
V=πPr4t8ηlV = \dfrac{\pi P r^4 t}{8 \eta l}
where h=h = height, S=S = surface tension, ρ=\rho = density, P=P = pressure, V=V = volume, η=\eta = coefficient of viscosity, ν=\nu = frequency and I=I = moment of inertia.

Options

  1. AThe equation is dimensionally incorrect, as the right side has dimensions of [ML2T−2][M L^2 T^{-2}].
  2. BThe equation is dimensionally incorrect, as the right side has dimensions of [L2][L^2].
  3. CThe equation is dimensionally correct.
  4. DThe equation is dimensionally incorrect, as the right side has dimensions of [L3T−1][L^3 T^{-1}].

Correct answer

C. The equation is dimensionally correct.

Step-by-step solution

The dimensions of the terms are evaluated as follows:

[V]=[L3][V] = [L^3]

[P]=[ML−1T−2][P] = [M L^{-1} T^{-2}]

[r]=[L][r] = [L]

[t]=[T][t] = [T]

[η]=[ML−1T−1][\eta] = [M L^{-1} T^{-1}]

[l]=[L][l] = [L]

Substituting these dimensions into the right hand side of the given equation:

[ML−1T−2][L4][T][ML−1T−1][L]=[ML3T−1][ML0T−1]=[L3]\dfrac{[M L^{-1} T^{-2}] [L^4] [T]}{[M L^{-1} T^{-1}] [L]} = \dfrac{[M L^3 T^{-1}]}{[M L^0 T^{-1}]} = [L^3]

Since the dimensions of the left hand side and right hand side are equal, the equation is dimensionally correct.
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