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NEET
Exam
NEET
Subject
Physics
Chapter
Units and Dimensions

NEET · Physics · Units and Dimensions

A theoretical model suggests that the power P generated by a wind...

A theoretical model suggests that the power PP generated by a wind turbine depends on the blade length LL, wind speed vv, air density ρ\rho, and the acceleration due to gravity gg. If the relationship is given by P∝LαvβργgδP \propto L^\alpha v^\beta \rho^\gamma g^\delta, which of the following sets of exponents is dimensionally consistent?

Options

  1. Aα=3,β=2,γ=1,δ=0\alpha=3, \beta=2, \gamma=1, \delta=0
  2. Bα=2,β=2,γ=1,δ=0\alpha=2, \beta=2, \gamma=1, \delta=0
  3. Cα=3,β=3,γ=1,δ=0\alpha=3, \beta=3, \gamma=1, \delta=0
  4. Dα=2,β=3,γ=1,δ=0\alpha=2, \beta=3, \gamma=1, \delta=0

Correct answer

D. α=2,β=3,γ=1,δ=0\alpha=2, \beta=3, \gamma=1, \delta=0

Step-by-step solution

Write the dimensional formula for each physical quantity:
Power P=[ML2T−3]P = [M L^2 T^{-3}]
Length L=[L]L = [L]
Velocity v=[LT−1]v = [L T^{-1}]
Density ρ=[ML−3]\rho = [M L^{-3}]
Acceleration due to gravity g=[LT−2]g = [L T^{-2}]

Using the principle of dimensional homogeneity:
[ML2T−3]=[L]α[LT−1]β[ML−3]γ[LT−2]δ[M L^2 T^{-3}] = [L]^\alpha [L T^{-1}]^\beta [M L^{-3}]^\gamma [L T^{-2}]^\delta
[ML2T−3]=[MγLα+β−3γ+δT−β−2δ][M L^2 T^{-3}] = [M^\gamma L^{\alpha + \beta - 3\gamma + \delta} T^{-\beta - 2\delta}]

Equating the powers of MM, LL, and TT on both sides:
For MM: γ=1\gamma = 1
For TT: −β−2δ=−3⇒β+2δ=3-\beta - 2\delta = -3 \Rightarrow \beta + 2\delta = 3
For LL: α+β−3γ+δ=2\alpha + \beta - 3\gamma + \delta = 2

Substitute γ=1\gamma = 1 into the LL equation:
α+β−3(1)+δ=2⇒α+β+δ=5\alpha + \beta - 3(1) + \delta = 2 \Rightarrow \alpha + \beta + \delta = 5

Now check the given options to see which satisfies both β+2δ=3\beta + 2\delta = 3 and α+β+δ=5\alpha + \beta + \delta = 5:
Option 4 gives α=2,β=3,γ=1,δ=0\alpha=2, \beta=3, \gamma=1, \delta=0.
β+2δ=3+0=3\beta + 2\delta = 3 + 0 = 3 (Satisfied)
α+β+δ=2+3+0=5\alpha + \beta + \delta = 2 + 3 + 0 = 5 (Satisfied)
Thus, this is the correct set of exponents.

Answer: α=2,β=3,γ=1,δ=0\alpha=2, \beta=3, \gamma=1, \delta=0
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