Measurement Errors and Measurement Uncertainties

Question 1

what is a random error

Answer 1

• an error caused by unpredictable changes in conditions
• such as temperature or pressure
• or in a difference in recording that is accurate to get exactly right

Question 2

what is a systematic error

Answer 2

• an error caused by the apparatus

- which leads to the recorded value being either too high or low

Question 3

a volume of gas is collected in a syringe and measured in different experiments done on the same day. what random error could occur here

Answer 3

• the temperature or atmospheric pressure of the lab may vary during the day
• this will cause an unpredictable change in the value recorded

Question 4

why does repeating an experiment lead to a more accurate final value

Answer 4

because these random fluctuations in conditions are less important when values are averaged

Question 5

what is an example of a systematic error occurring with a thermometer

Answer 5

• the thermometer might have more liquid in it than it should have
• causing the height of the liquid at all temperatures to be higher than it should be
• meaning the recorded temp will always be higher than the correct temp

Question 6

will repeating experiments where you have a systematic error make any difference and why

Answer 6

• no
• because the problem is with the equipment itself
• you can repeat it as many times as you want, but if the instrument in which you are recording your values isnt accurate
• you will always have an incorrect answer

Question 7

when recording the meniscus of a liquid at eye level, how would random and systematic errors arise

Answer 7

• the random error would be small variations from the horizontal when measuring at eye level
• the systematic error could be consistently reading the meniscus from above or the wrong angle
• so no matter how accurate or precise even the instruments are, you will always get an inaccurate answer

Question 8

what is the inherent potential error of any apparatus called

Answer 8

their measurement uncertainty

Question 9

what is the size of the measurement uncertainty determined by

Answer 9

the precision of the apparatus

Question 10

if a balance that uses three decimal places is more precise than one that uses one decimal place, how do their measurement uncertainties compare

Answer 10

the balance with three decimal places has a lower measurement uncertainty than the one decimal balance

Question 11

if the measurement uncertainty of the one decimal place balance is 0.05g and for the three decimal place its 0.0005g, and they were both used to measure 10g of a substance, how would you mathematically show that the three decimal place balance is more accurate

Answer 11

• by calculating their percentage uncertainties
• (0.05 / 10) x 100 = 0.5% uncertainty
• (0.0005 / 10) x 100 = 0.005% uncertainty
• the 3dp one has a percentage U of 0.005% whereas the other one has one of 0.5%

Question 12

if the one decimal place balance can read to one decimal place, why is the uncertainty said to be +-0.05g

Answer 12

• because it can measure the mass to be a little too high or a little too low due to rounding up or down
• so its range of 0.1 that it can measure it split into two
• meaning it can read the mass to be 0.05 too high or 0.05 too low

Question 13

what could a reading of 17.1g be between for that balance

Answer 13

17.05 and 17.15g

Question 14

if the measurement uncertainty of a 50cm^3 burette is 0.05cm^3, what would the uncertainty be when it is practically used and why

Answer 14

• it would be 0.1cm^3
• because you are reading the burette twice
• from the initial value to the final reading
• because you do it twice you double the uncertainty