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 is B

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