PROPERTIES OF LIQUIDS AND SOLIDS

Answer :

F = (2AT / d)

                   A = area = 10^–2 m²

                   T = surface tension = 70 × 10^–3 N/m

                   d = thickness of water film between plates = 0.05 × 10^–3 m

                   hence

                             F = {(2 × 10^–2 × 70 × 10^–3) / (0.05 × 10^–3)} = 28 N   

Answer :

Surface tension decreases with temperature, presence of soap also reduces it. It varies with concentration of liquid.   

Answer :

                   Weight of metal disc = total upward force = up thrust force + force due to

                   surface tension

                                      = weight of displaced water + T cos θ(2πr)

                                      = w + 2πr T cos θ

Answer :

Force of surface tension acting on slider balances the force due to weight.

                   If T is force due to surface tension per unit length, then F = T × 2L

                   Where L is length of wire. As film has got two surfaces. Length is Taken

                   as 2L      

                             ∴ F = T × 2L = W

                             ∴ T = (W / 2L)

                                   = {(1.5 × 10^–2) / (2 × 0.3)}

                                   = 2.5 × 10^–2 N-m   

Answer :

In case of soap bubble, workdone =8πT(r₂² – r₁²)

                   Here r₁ = r   and r₂ = 2r

                   ∴ workdone = 8πT(4r² – r²)

                   workdone = 24πr²T

                   i.e. energy needed in 24πr²T