A1-1: Measurements and Accuracy


Microscope slide; vernier calipers; magnifying glass; micrometer; beam balance with masses; Archimedes’ bridge; beaker of water (\(250\text{ml}\)); metre ruler.


For each of the following, record the observations together with the possible error (i.e. ½ the smallest scale division), e.g.: \(46 \pm 0.5\text{mm}\). Calculate the mean value of repeated readings together with the error. Calculate the % error.

  1. Measure the slide thickness in a number of places using the metre ruler.
  2. Repeat using the vernier calipers instead.
  3. Measure the slide thickness in several places using the micrometer. For a mechanical micrometer, record the ‘zero reading’ and adjust the other readings correctly.
  4. Measure the length \(l\) and the width \(w\) using the metre ruler. Find the mass of the slide in air \(m\) , and then its apparent mass when suspended in water \(m_a\).


\[\begin{split}\text{upthrust} &= \text{weight of liquid displaced} \\ mg - m_a g &= \rho_w g \ \big(\text{slide volume}\big)\end{split}\]


\[\begin{split}\text{slide volume} = \frac{m - m_a}{\rho_w} \\ \rho_w = \text{density of water}\end{split}\]

Then calculate the slide thickness \(d\) since:

\[l w d = \text{slide volume}\]

When you have completed the above, arrange the estimates of slide thickness in order (most accurate first).

Explain carefully why some methods are more accurate than others.