2.2 Making Measurements & Analysing Data

Question 1

what is accuracy?

Answer 1

how close a value is to the commonly accepted value or TRUE VALUE

Question 2

what is precision?

Answer 2

relates to how close together repeat values are, smaller the range = more precise

Question 3

what is a systematic error?

Answer 3

this includes (zero errors), these are errors that are the same every time you repeat the experiment, (they shift the values by the same amount), usually due to incorrect calibration of equipment, they affect the accuracy but not the precision of your results

Question 4

what is a random error?

Answer 4

an error caused by unknown and unpredictable changes during an experiment, can be caused by changes in instruments or in the environment (e.g fluctuations in temperature), they affect both precision and accuracy

Question 5

what is a human error?

Answer 5

a one-off mistake, an anomalous result caused by human mistakes that can be removed

Question 6

what is an uncertainty?

Answer 6

an error in a piece of measuring equipment which could change measurements (e.g due to a lack of sensitivity)

Question 7

what is the absolute uncertainty for single readings?

Answer 7

+- the resolution, the smallest division on the measuring equipment used (the smallest change it can read)

Question 8

what is the absolute uncertainty for several/a group of readings?

Answer 8

0.5 x the range, or half the spread to find absolute uncertainty

Question 9

what is the formula for percentage uncertainty for single readings?

Answer 9

absolute uncertainty/measured value x 100

Question 10

what is the formula for percentage uncertainty for a group of readings?

Answer 10

absolute uncertainty/mean of values x 100

remember here the absolute uncertainty = 0.5 x range

Question 11

when combining percentage uncertainties, what is the rule?

y=a+/-b

Answer 11

percentage uncertainty of a + percentage uncertainty of b

Question 12

when combining percentage uncertainties, what is the rule?

y=ab

Answer 12

percentage uncertainty of a + percentage uncertainty of b

Question 13

when combining percentage uncertainties, what is the rule?

y=a/b

Answer 13

percentage uncertainty of a + percentage uncertainty of b

Question 14

when combining percentage uncertainties, what is the rule?

y=a^n

Answer 14

percentage uncertainty of a x n

Question 15

how do you represent uncertainty of individual values on graphs?

Answer 15

plot error bars on each point (shows the range where the true value is likely to lie in)

Question 16

how you work out the percentage uncertainty of a gradient of a line or the y-intercept of a line?

Answer 16

• first plot all points and add error bars to each points
• draw a line of best fit through as many of the points as you can (ensure it passes through all the error bars)
• calculate the gradient of the LOBF
• then draw a line of maximum gradient and minimum gradient (lines of worst fit that still go through all the error bars)
• absolute uncertainty = 0.5 x (max gradient - min gradient) OR (best gradient - one of the worst gradient)
• percentage uncertainty = absolute uncertainty/gradient of LOBF x 100

(DO EXACTLY THE SAME THING FOR Y-INTERCEPT)

Question 17

what is a zero error?

Answer 17

when the apparatus or equipment shows a non-zero value when it should be registering a value at exactly zero

Question 18

give an example of a systematic error

Answer 18

parallax errors, caused by reading a scale at a wrong angle, for example when your eye is not parallel with the meniscus when measuring a liquid in a cylinder