Uncertanties

Question 1

Define the term ‘scale reading uncertainty’.

Answer 1

Gives an indication of how precisely a scale on a measuring instrument can be read. It depends on the type of scale used – analogue or digital.

Question 2

Write down the rule for finding the reading uncertainty in an analogue scale.

Answer 2

Reading uncertainty = ± 1/2 of the smallest scale division

Question 3

Write down the rule for finding the reading uncertainty in a digital scale.

Answer 3

Reading uncertainty = ± 1 of the least significant digit

Question 4

Define the term ‘mean’.

Answer 4

The best estimate of the ‘true’ value of the quantity being measured.

Question 5

Write down the equation used to calculate the mean of a set of repeated measurements.

Answer 5

Sum of measurements/number of measurements

Question 6

Define the term ‘random uncertainty’.

Answer 6

Arises when measurements are repeated and slight variations occur. Random uncertainty may be reduced by increasing the number of repeated measurements.

Question 7

Random uncertainty may be reduced by ____________ the number of repeated measurements.

Answer 7

Increasing

Question 8

Write down the equation used to calculate random uncertainty.

Answer 8

Max Value-Min Value/Number of Readings

Question 9

Define the term ‘systematic uncertainty’.

Answer 9

Occurs when readings taken are either all too small or all too large. This can arise due to faulty measurement techniques or experimental design.

Question 10

Describe a situation which could lead to a systematic uncertainty in a measurement.

Answer 10

Faulty measuring instrument/poor design of an experiment/failure to zero or calibrate an instrument correctly/experimenter making the same mistake each time

Question 11

A graph shows a directly proportional relationship between two variables. Sketch a different graph to show how the original graph would look if there was a systematic uncertainty in the measurements for one of the variables. No numerical values are required on the axes.

Question 12

Describe how you would write a measurement and its uncertainty in absolute form.

Answer 12

Measurement ± uncertainty (or in brackets with unit appearing after)

Question 13

When we want to compare uncertainties, which form of uncertainty should we use?

Answer 13

Percentage uncertainties

Question 14

Describe how to calculate percentage uncertainty when given a reading in absolute form (measurement ± uncertainty).

Answer 14

(Uncertainty/final value)x100

Question 15

Write down the rule for determining the overall uncertainty in a final result.

Answer 15

Choose the largest percentage uncertainty.