Topic 2.2 Errors and Uncertainties

Question 1

What is accuracy?

Answer 1

The degree to which a measurement approaches the ‘true value’.

Question 2

What is precision?

Answer 2

Precision is determined by the size of the random error in the measurements.

Question 3

What is the uncertainty?

Answer 3

The total range of values within which the measurement is likely to lie.

Question 4

Instrument uncertainty examples?

Answer 4

Stopwatch with 0.1 s divisions = /-+/ 0.1 s
Thermometer with 1 °C intervals = 0.5 °C
Ammeter with 0.1 A divisions = 0.1 A

Question 5

Examples of systematic error?

Answer 5

1. Zero error on an instrument.
2. Wrongly calibrated scale.
3. Reaction time of experimenter.

Question 6

Example of random error?

Answer 6

1. Error in reading the scale.
2. Timing oscillations without the use of a reference marker.
3. Taking the readings of a quantity that varies with time.
4. Parallax error.

Question 7

Combining Uncertainties

Answer 7

1. For quantities which are added or subtracted, add the ACTUAL uncertainties.
2. For quantities which are multiplied together or divided, add the fractional uncertainties.

For x = (Ay^a z^b): Δx/x = a(Δy/y) + b(Δz/z)
For x = y + z: Δx = Δy + Δz