1,000 identical drops of oil of density 500kgm-3 have a total mass of 5 x 10-4kg. One of the drops forms a thin film of area 0.5m2 on water. The thickness of the film is
-
A.
2 x 10-8m -
B.
2 x 10-9m -
C.
2 x 10-7m -
D.
3 x 10-9m -
E.
2.8 x 10-8m
Correct Answer: Option B
Explanation
Mass of one oil = (frac{5 times 10^{-4}}{1000})
= 5 x 10-4kg
Density = (frac{text {mass}}{text{area x thickness}})
500 = (frac{5 times 10^{-7}}{text{0.5 x thickness}})
thickness = 2 x 10-9m