A drop of water of mass m , surface tension T , is trapped between two parallel glass plates, separated by distance d . The force needed to separate the plates, to pull them apart, perpendicular to the plane of plates, is

Question

A drop of water of mass m , surface tension T , is trapped between two parallel glass plates, separated by distance d . The force needed to separate the plates, to pull them apart, perpendicular to the plane of plates, is, 2 T m π d 2 ρ, 2 T m d 2 ρ, T m 2 d 2 ρ, T m 2 π d 2 ρ

MARKS App · Accepted Answer

Pressure inside the liquid film is smaller than outside by Δ P = T r = T c o s θ d 2 = 2 T c o s θ d , F = Δ P × A = A × 2 T c o s θ d m = A × d × ρ ⇒ A = m d × ρ ⇒ F = 2 T c o s θ d × m d ρ = 2 T m c o s θ d 2 ρ ⇒ F = 2 T m d 2 ⋅ ρ

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