Data and Uncertainties

Question 1

Readings

Answer 1

The values found from a single judgment when using a piece of equipment

Question 2

Measurements

Answer 2

The values taken as the difference between the judgments of two values

Question 3

Assessing uncertainty

Answer 3

Resolution of the instrument used

Manufacturer’s tolerance on instruments

Judgements that are made by the experimenter

The procedures adopted (e.g. Repeated readings)

Size of increments available

Question 4

Uncertainty in a reading

Answer 4

At least plus or minus half of the smallest division

Question 5

Uncertainty of a measurement

Answer 5

At least plus or minus one of the smallest divisions

Question 6

Uncertainties in given values

Answer 6

E.g. Charge of an electron is given as 1.60x10^-19

Uncertainty is + or - 0.01x10^-19

Assume he uncertainty to be plus or minus 1 in the last significant digit

Question 7

Repeated measurements

Answer 7

A method for reducing the uncertainty

Uncertainty in this case = half the range

Question 8

Uncertainties from gradients

Answer 8

Percentage uncertainty = (best gradient - worst gradient) X 100 /best gradient

Question 9

Error bars in physics

Answer 9

Plot data points at their
mean value

Calculate the range of data ignoring any anomalies

Add error bars with lengths equal to half the range

Question 10

Variable and graph axis

Answer 10

X axis - independent variable (the variable that caused the observed effect) it isn’t affected by the other variable

Y axis - dependent variable (the variable that was effected by the independent variable)

Question 11

Scientific ideas

Answer 11

The scientific community only accepts new ideas when they can be independently validated

This means others are able to reach the same conclusion

Question 12

Uncertainties in using immersion heater experiment to calculate specific heat capacity

Answer 12

Temperature varies throughout - stir

Some of the input energy is use to raise the temperature of the heater and the container

Temperature will continue to rise after the heater has been turned off - find max temperature

Uncertainties in ammeter, voltmeter and thermometer

Question 13

Combining uncertainties

Answer 13

If you are adding or subracting values you add the absolute uncertainties

If you are dividing or multiplying then you add the percentage uncertainties

If you are raising a number to a power then you multiply the percentage uncertainties by that power

Question 14

Advantages of using data loggers

Answer 14

More accurate data
Higher sampling rate
Data can be displayed in real time

Question 15

Random errors

Answer 15

These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next.

Random errors are present when any measurement is made, and cannot be corrected. The effect of random errors can be reduced by making more measurements and calculating a new mean.

Question 16

Systematic errors

Answer 16

These cause readings to differ from the true value by a consistent amount each time a measurement is made.
Sources of systematic error can include the environment, methods of observation or instruments used.

Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared.

Question 17

Zero errors

Answer 17

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero, eg the needle on an ammeter failing to return to zero when no current flows.

A zero error may result in a systematic uncertainty.

Question 18

Anomalies

Answer 18

These are values in a set of results which are judged not to be part of the variation caused by random uncertainty

Question 19

Precision

Answer 19

Precise measurements are consistent, they fluctuate slightly about a mean value - this doesn’t indicate the value is accurate

The closeness of measurements to one another

Question 20

Resolution

Answer 20

The smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading

Question 21

Accuracy

Answer 21

The level of conformity of a measurement to the actual value

Question 22

How to determine if something is vertical ?

Answer 22

Use a plumb line

Use a spirit level

Question 23

Reducing uncertainty

Answer 23

Take multiple readings / measurements

Longer time/distance/relevant variable - reduces percentage uncertainty

Question 24

Percentage uncertainty in a y intercept

Answer 24

Same method as a gradient

Best intercept - worst intercept/best intercept x 100

Question 25

Measurement error

Answer 25

The difference between a measured value and the true value

Question 26

Evidence Fair test Hypothesis Prediction

Answer 26

Data that has been shown to be valid A test in which only the independent variable has been allowed to affect the dependent variable A proposal intended to explain certain facts or observations A statement suggesting what will happen in future, based on observation, experience or a hypothesis

Question 27

Interval

Answer 27

The quantity between readings e.g. a set of 11 readings equally spaced over 1 m would give an interval of 0.1 m

Question 28

Repeatable

Answer 28

An experiment is repeatable if the original experimenter repeats the experiment using the same method and obtains the same results

Question 29

Reproducible

Answer 29

A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained

Question 30

Uncertainty

Answer 30

The interval within which the true value can be expected to lie, with a given level of confidence or probability

Question 31

Validity

Answer 31

Suitability of the investigative procedure to answer the question being asked

Question 32

Valid conclusion

Answer 32

A conclusion supported by valid data, obtained from an appropriate experimental design and base on sound reasoning

Question 33

Categoric variables

Answer 33

Have values that are labels e.g. names of plants

Question 34

Continuous variables

Answer 34

Can take on any values (infinite number of values) Given magnitude by counting or by measurement

Question 35

Control variables

Answer 35

A varaible which may, in addition ot the indepedent variable affect the outcome of the investigation and therefore has to be kept constant or monitored

Question 36

Dependent variables Independent variables

Answer 36

The variable of which the value is measured for each and every change in the independent variable - it is affected by the independent variable The variable for which values are changed or selected by the experimenter - affects the dependent variable

Question 37

Nominal variables

Answer 37

A type of categoric variable where there is no ordering of categories

Question 38

Reliability

Answer 38

Reliable experiments produce consistent and stable results.

Question 39

How does decreasing the time base of the oscilloscope reduce uncertainty?

Answer 39

Waveform will be stretched in the y axis Resolution of the time axis increases Increases the length/distance measured across the screen reduces percentage uncertainty in the reading of time

Question 40

Validated evidence

Answer 40

Data collected from an experiment used to test a theory The results of the experiment are consistent and deemed reliable - they are able to be replicated/independently validated

Question 41

Things to consider when criticising data tables

Answer 41

Number of significant figures and consistency Range of data used Intervals used - are they consistent? Number of values used Number of repeats

Question 42

Fundamental SI base units

Answer 42

mass - kilograms (kg) time - seconds (s) amount of substance - mol temperature - kelvin (K) length - metres (m) electric current - amperes (A)