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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Physics
Chapter
Units and Dimensions

NTA Abhyas 2020 · Physics · Units and Dimensions

The dependency of speed of water surface waves (capillary waves) on...

The dependency of speed of water surface waves (capillary waves) on the density of water (ρ)( ρ ) their wavelength (λ)( \lambda ) and surface tension (γ)( \gamma ) is -

Options

  1. A\gammaaρ\sqrt{\dfrac{\gammaa}{ρ}}
  2. Bγρλ\sqrt{\dfrac{\gamma}{ρ\lambda}}
  3. C{\left(\dfrac{\gamma}{ρ\lambda}\right)}^{\dfrac{1}{3}}
  4. Dγρλ\dfrac{\gamma}{ρ\lambda}

Correct answer

B. γρλ\sqrt{\dfrac{\gamma}{ρ\lambda}}

Step-by-step solution

Velocity of surface waves depends on density of water, its own wavelength of surface tension.

v∝ρaλbγcv ∝ {ρ}^{a}{\lambda}^{b}{\gamma}^{c}

\left[LT^{- 1}\right] ∝ {\left[ML^{- 3}\right]}^{a}{\left[L\right]}^{b}{\left[\dfrac{MLT^{- 2}}{L}\right]}^{c}<br/><br/>[LT−1]∝Ma+cL−3a+bT−2c<br /><br />\left[LT^{- 1}\right] ∝ M^{a + c}L^{- 3a + b}T^{- 2c}

a+c=0..........(i)a + c = 0 ..........(i)

−3a+b=1.............(ii)- 3a + b = 1 .............(ii)

−2c=−1.............(iii)- 2c = - 1 .............(iii)

Solving
a=−12,b=−12,c=12,a = - \dfrac{1}{2}, b = - \dfrac{1}{2}, c = \dfrac{1}{2 ,}

v∝ρ−12λ−12γ12v ∝ {ρ}^{- \dfrac{1}{2}}{\lambda}^{- \dfrac{1}{2}}{\gamma}^{\dfrac{1}{2}}

v∝γρλv ∝ \sqrt{\dfrac{\gamma}{ρ\lambda}}
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