Types of Measurement Error
You need to be familiar with the three types of measurement error in all three subjects, but especially in Physics.
There are only three types, and if you are asked to state a type of error in any question, you should respond with one of these.
Important!
‘Human error’, which is often quoted by students, is not a recognised type of error and is very likely to be marked incorrect.
1. Random Error
Random errors are unpredictable differences between your readings and the true value. For example, if you are timing a swinging pendulum with a stopwatch, your reaction time will be slightly different every single time you press the button. This leads to a (random) spread of readings around the true value.
Because each error may be too high or too low completely by chance, you can’t completely eliminate them. However, you can easily reduce their impact by taking multiple repeat readings and calculating a mean (average)
2. Systematic Error
Systematic errors are consistent, predictable mistakes that cause your readings to be wrong by the exact same amount every single time. This usually happens because of a flaw in the equipment or a mistake in how the experiment is set up. For instance, if you are reading the volume of water in a measuring cylinder but always look at it from a high angle instead of eye level (known as parallax error), all your results will be consistently too high. Because the error is always the same, taking repeats and calculating a mean will not fix it; you have to change your technique or fix the equipment.
3. Zero Error
A zero error is an instrument error. It is a type of systematic error that happens when a measuring instrument gives a false reading when it should be showing exactly zero. Think of an ammeter which reads 0.2 A even before you put it into a circuit. In this case when you do put it into a circuit, every reading you take from it will be 0.2 A too high.
In the lab, this often happens with digital ammeters, voltmeters, balances, or micrometer screw gauges. To fix a zero error, you either need to reset the equipment using a “tare” or zero button, or simply subtract (or add) the false reading from all your final results.
Ammeter with Zero Error
