tricky PPQ's

Question 1

Apparatus uncertainty of a ruler

Answer 1

Ruler has uncertainty of + or - 0.5mm as its half the smallest division.
When you measure with a ruler, you take 2 measurements, one on either end, e.g. 0mm and 3mm gives 3 mm measurement. Therefore, uncertainty is 0.5 X 2= 1mm

Question 2

Calc uncertainty of actual length (8micrometers)
length measured with a ruler (4mm)

Answer 2

do uncertainty divided by measured length
so 1/4= 0.25 X 100= 25% percentage uncertainty
25% of 8= 2 micro meters which is uncertainty of our calculated actual length