# Percentage uncertainties

Converting from an absolute uncertainty to a percentage uncertainty give us a much better idea of whether our results are reliable or not.

In general, any result with a percentage uncertainty of 10% or less can be considered reliable.

You will often need to convert things into percentage uncertainties in order to compare reliability.  They like you to do this in the exam AND WILL SOMETIMES GET YOU TO REFERENCE PREVIOUS UNCERTAINTY CALCULATIONS WHEN ASKING FOR AN EVALUATION OF WHICH METHOD IS BETTER.  So, as always, read the questions carefully!

Watch the video below and then have a go at the practice questions.  When you are ready, go on to exercise 3.

## PRACTICE QUESTIONS

1) You measure a block with a ruler that  has a precision of 1mm. You obtain a length of 2.4cm.

a) What is the absolute uncertainty in this measurement?

b) What is the percentage uncertainty in this measurement?

2) The following range of results is obtained for the mass of a bouncy ball:

13.2g, 13.4g, 13.3g, 13.4g, 13.2g, 13.3g

a) Calculate a value for the mass of the bouncy ball.

b) What is the absolute uncertainty in these measurements?

c) What is the percentage uncertainty in these measurements?