Question

The force required to separate two glass plates of area 10^–2 m² with a film of water 0.05 mm thick between them is (surface tension of water is 70 × 10^–3 N/m) 

(A) 28 N 

(B) 14 N 

(C) 50 N 

(D) 38 N

Answer 1

Correct option: (A) 28 N

Explanation:

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