# A drop of oil volume 0.05cm^3 is released from a medicine dropper on to a calm surface of a pond where it spreads out to cover an area of 40cm^2

A drop of oil volume 0.05cm^3 is released from a medicine dropper on to a calm surface of a pond where it spreads out to cover an area of 40cm^2. Assume that the oil film has a uniform thickness equal to the diameter of an oil molecule. I see there is an answer to this query already, but I need to help in understanding how to go about the calculation. I divided the volume by the area but it doesn't match the answer given. I wouls be very grateful for some help.

Vol = 40 x h

We know Vol = 0.05

Re-arrange & substitute to get the answer

0.05cm^3/40cm*2= 1.25×10^-3 cm

= 1.3×10^-3 to 2 sig figs is this correct as it seems to be diiferent to the answer given for this question else where on this forum of 0.001275cm rounding to 0.0013cm 0r 1.3 x 10^-3

The only comment in addition is significant figures, if you have to worry about those, then since you started with only one sig figure, the answer will be limited to one. Otherwise, to two sig figures, 1.3E-3 cm would be the answer.

Thanks everyone

Looking at it again, yes i have to write it to the approriate sig fig get mixed up with these have to write it in notation so to 1 sig fig would that be 1.0E-3cm

Just to clear up a couple of things since my response may be the one to which you refer (along with the poster). Yes, the answer we had, disregarding s.f. was 0.001275 or 1.275 x 10^-3 cm. The original answer had been changed to mm and that was incorrect. You may have missed that point. AND your answer of 1.3 x 10^-3 to two significant figures is EXACTLY the same thing in your post as it is in what you quote as being different.

Second thing: The numbers in the original question which I helped with were 0.051 volume (not 0.05 as in your post) and 25o C. Both of these number have two s.f.; therefore, two s.f. are allowed and that gives us 0.001275 cm rounded to two s.f. = 0.0013 cm or in scientific notation 1.3 x 10^-3 cm.

The point I am making here is that both problems are correct. They started with slightly different numbers.

Yes, I realised my mistake there, can't see the figures for the figures been working too hard.Thanks anyway for pointing it out.

One point I forgot to mention is that your answer of 1.0E-3 is still writing the answer to two s.f. To one would be 1E-3.

Good luck.

Whats the differnce between scientific theory and a regulr theory?