Topic 1.2: Uncertainties and Errors Flashcards
What are systematic errors?
Any error caused by the measuring system
Measurements give identical error for each reading
It can not be reduced by repetition
e.g., pointer on voltmeter doesn’t read 0
What are random errors?
Variations of measurements by instrument or operator
Random errors can be reduced by repetition
e.g., mesuring diameter of a wire many times in different positions
What is ACCURACY?
Accurate values are close to the accepted value
They have a small sysematic error
e.g., calculating gravity as 9.7 when the expected value is 9.8 (difference between the calculated value and expected is 0.1) (very accurate)
What does % difference tells us?
Tells how accurate the data is
The lower the % difference the more accurate the result
What is PRECISION?
Precise values are close to each other
They have small random error
e.g., values of gravity were calculated as 10.9, 11.0 and 11.1 (difference between the values are 0.1) (precise but not accurate)
What does the number of significant figures tell us?
The number of s.f. reflects the precision of a value or input data (significant figure interlude)
The number of s.f. in a calculation is the least precise value
What is a range of readings?
The difference between the biggest and the smallest readings
How do you esimate uncertainties with ANALOG meters?
You look at the divisions (the smallest value on the meter) then divide it by 2
example of divisions, a thermometer increases by 1 since there is a line for each 1 value on a thermometer
How do you estimate uncertainties with DIGITAL meters?
The minimum uncertainty is equal to the last digit of a digital meter
example, digital meter shows 3.21, minimum uncertainty is ± 0.01
WHY do you calculate the percentage uncertainty?
Calculating the percentage uncertainty in a result or reading and comparing it to the known or accepted value is a good method of finding how accurate the experiment was
How do you calculate the % DIFFERENCE between experiment and accepted value?
(accepted value - calculated value / accepted value) * 100
percentage difference is not the total percentage uncertainty
What is an anomaly?
An anomaly is a result that does not follow the pattern of the other values
How do you add / subtract uncertainties?
You add the absolute uncertainties
What are absolute uncertainties?
The regular uncertainties (e.g., ± 0.1)
How do you multiply / divide uncertainties?
You add the % uncertainties
