Physics Uncertainties and Errors

Question 1

Error

Answer 1

Error in measurement is expected because of the imperfect nature of us and our measuring devices

Question 2

Uncertainty, aka absolute uncertainty

Answer 2

Uncertainty (aka absolute uncertainty) is the interval within which the true value of a quantity can be expected to lie

Question 3

Resolution

Answer 3

The resolution of a measuring tool is the smallest distance between two points that can be distinguished, i.e. the smallest change in a quantity that can be seen
- Example: resolution is 1mm of an average ruler

Question 4

Writing the uncertainty

Answer 4

The uncertainty of a measuring instrument is estimated as plus or minus (±) the smallest scale division (or half the resolution)
- For a thermometer with a mark at every 1.0°C, the uncertainty is ±0.5°C

Question 5

Random error

Answer 5

Random error is due to the recorder, rather than the instrument used for the measurement

Question 6

Minimizing random error

Answer 6

To minimize random errors, take many readings of the same measurement and calculate a mean average

Question 6

Causes of random error

Answer 6

• Person’s reaction time
• Ruler wasn’t lined up
• Person was viewing the beaker from the wrong angle

Question 6

Systematic error

Answer 6

Systematic error is an error due to the instrument being “out of adjustment”

Question 7

Causes of systematic error

Answer 7

Systematic errors are usually difficult to detect as our results would usually be close to each other. We can help to spot this by comparing our data with each other or to known values (where available). Other possible causes:
- Voltmeter might have zero offset error (incorrectly calibrated)
- Meter stick might be rounded on one side
- Newton meter spring might be old or stretched

Question 8

Accuracy

Answer 8

Measurements are close to the true value

Question 9

Precise

Answer 9

Measurements are similar each time

Question 10

Accuracy vs precision

Answer 10

Accurate: Measurements are close to the true value
Precise: Measurements are similar each time

Question 11

Repeatability

Answer 11

Repeatable results - if one person does the same experiment and gets similar results

Question 12

Reproducibility

Answer 12

Reproducible results - if different people do the same experiment and get similar results

Question 13

Repeatability vs reproducibility

Answer 13

Repeatable results - if one person does the same experiment and gets similar results
Reproducible results - if different people do the same experiment and get similar results

Question 14

Reliability

Answer 14

For data to be reliable, repeats must be carried out

Question 15

Absolute error

Answer 15

Absolute error is the raw uncertainty or precision of your measurements
- Similar / the same as uncertainty

Question 16

Fractional error

Answer 16

Fractional error = Absolute error / measured value

Usually given as a decimal

Question 17

Percentage error

Answer 17

Percentage error = (Absolute error / measured value) * 100

The contents of the brackets is the same as fractional error
Percentage error is given as ±x%