Paper 3 Section A

Question 1

What is a random error?

Answer 1

Random errors cause readings to be spread about the true value due to the results varying in an unpredictable way.
They affect precision.
They can occur in any measurement and can’t be corrected
Could be due to noise, or that you can’t keep controlled variable exactly the same throughout the experiment.

Question 2

What is a systematic error?

Answer 2

Systematic errors cause each reading to be different to the true value by the same amount. They affect the accuracy of the results. Systematic errors are caused by the environment, the apparatus you’re using or your experimental method.

Question 3

What should you do if you suspect a systematic error?

Answer 3

Repeat the experiment with a different technique or apparatus and compare the results

Question 4

How can you reduce systematic error?

Answer 4

-Calibrate you apparatus by measuring a known value, if there’s a difference between the measured and known value, you can use this to correct the inaccuracy of the apparatus
-Calibration can also reduce zero errors

Question 5

How can you reduce random errors?

Answer 5

-Take repeats and find average- the more measurements you average over the less random error you’re likely to have
-Using computers and data loggers can get rid of any human errors
-Use equipment with an appropriate resolution

Question 6

What is precision?

Answer 6

The smaller the amount your data spreads from the mean, the more precise it is. Precision only depends on the amount of random error in your readings. Precise measurements are not necessarily accurate.

Question 7

What is repeatability?

Answer 7

If the original experimenter can repeat the experiment multiple times and get the same results then it is repeatable.

Question 8

What is reproducibility?

Answer 8

If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is reproductible

Question 9

What is resolution?

Answer 9

The smallest change in the quantity being measured that gives a recognisable change in reading

Question 10

What is accuracy?

Answer 10

A measurement close to the true value is accurate

Question 11

What is uncertainty?

Answer 11

The ​uncertainty​ of a measurement is the bounds in which the accurate value can be expected to lie

Question 12

What is the absolute uncertainty?

Answer 12

The size of the range of values that the ‘true’ value lies

Question 13

What is fractional uncertainty?

Answer 13

Uncertainty as a fraction of the original measurement.

Question 14

What is the percentage uncertainty

Answer 14

uncertainty as a percentage of the original value

Question 15

How to calculate the uncertainty of a reading vs measurement?

Answer 15

The ​uncertainty in a reading​ is ​ ​± half the smallest division​,
e.g. for a thermometer the smallest division is 1°C so the uncertainty is ±0.5°C.
The ​uncertainty in a measurement​ ​is ​at least ±1 smallest division,
e.g. a ruler, must include ​both​ the uncertainty for the start and end value, as each end has
±0.5mm, they are added so the uncertainty in the measurement is ±1mm.

Question 16

What is the uncertainty on a mean of repeated results?

Answer 16

half the range of the results

Question 17

Rules for combining uncertainties?

Answer 17

Adding or subtracting uncertainties- add the absolute uncertainties
Multiplying or dividing data- add the percentage uncertainties
Raising to a power- multiply the percentage uncertainties by the power

Question 18

Uncertainty in the gradient of a graph

Answer 18

The ​uncertainty in a gradient​ can be found by lines of best and worst fit, this is especially useful when the gradient represents a value such as the acceleration due to gravity:
● Draw a ​steepest and shallowest​ line of worst fit, it ​must​ go through all the error bars.
● Calculate the gradient of the line of best and worst fit, the uncertainty is the ​difference
between the best and worst gradients.
percentage uncertainty = |best gradient−worst gradient|/best gradient X 100

Question 19

Uncertainty in the y-intercept

Answer 19

When the best and worst lines have different y intercepts, you can find the ​uncertainty in the
y-intercept​, which is |best y intercept-worst y intercept|:
percentage uncertainty = |best y intercept−worst y intercept| /best y intercept X 100