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**1.**The lotus effect refers to self-cleaning properties that are a result of ultrahydrophobicity as exhibited by the leaves of "lotus flower". Dirt particles are picked up by water droplets due to the micro- and nanoscopic architecture on the surface, which minimizes the droplet's adhesion to that surface. If the apparent contact area of a droplet with such a surface is A, and the real contact area because of the microscopic whiskers is xA with x = 0.003, what is the contact angle? Assume that without “whiskers”, the contact angle would be α0 = 110 ◦ .

**2. F = σa**

U = Sσ

U = Sσ

**3.**I tried to use the fact that the volume is being constant, and I assumed that the drop has the shape of a spherical cap, so I expressed it's volume in terms of contact angle.

A/xA=pi*R^2/pi*r^2

V=const

V=pi/3*R^3*(2+cos(a))(1-cos(a))^2=pi/3*r^3*(2+cos(b))(1-cos(b))^2

**But the equation I have obtained which is not solvable. Can you help me and show another approach?**
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