The size of atoms

 

IN LAB, we've been using some material from "Explorations in Physics" by David Jackson, Priscilla Laws and Scott Franklin. (Creative Commons Share-Alike, attribution license), specifically, from their Unit C on Heat, Temperature, and Cloud Formation

The size of atoms

In this activity, we'll estimate the size of atoms (using pepper and soap, Section 2.1.1).

    We measured across the region cleared of pepper to be approximately 13 cm. Take this as roughly the *diameter* of a circle. Use this, and the diameter of the starting "drop" according to the lab photograph to estimate the length, $h$, of a soap molecule.

    Report your results in both millimeters and meters.

[Here's a video of the demonstration (and calculation result) from a covid year]:

We're going to estimate the original size of the drop according to figure 2.6. $r_\text{sphere}\approx 0.15mm$. (If you used a slightly different number, that's OK.)


I estimated the pepper-free region as a circle, with its diameter extending on the ruler from 14 to 10.5cm, that is $14.0-10.5=3.5$ cm$=35$ mm

I found a thickness of 0.00001... mm = $1\times 10^{-5}$ mm..

$$h=V/A=\frac{\frac 43 \pi 0.15^3}{\pi(17.5)^2}$$ This is 0.00001... mm