Measurements Flashcards
What is the observed value?
True value + error
Systematic errors
- Follows a set pattern
EG: 0 error - all results are off, not a set 0 scale. - Hard to avoid :
Use measuring equipment to measure known value
Subtract error or repeat
-Cannot be reduced by repeats
What is random error?
- Follows no set pattern
It’s reading equipment wrong - Lots of repeats reduce random error
Tm- Terametre
10^12
G - giga
10^ 9
M -mega
10^6
Kilo
10^3
c - centi
10^-2
m- milli
10^-3
Micro - um
10^-6
Nano- n
10^-9
Pico- pm
10^ -12
Fento-fm
10^-15
Absolute uncertainty
1) If you only have one reading, or all repeat readings are the same, the absolute uncertainty is +- smallest increment.
- Eg: stick measured width with ruler 25+-1mm
2) If repeat readings are different, absolute uncertainty is +- (range/2)
E.G; width of a stick measured with vernier capilar (precision 0.1mm)
Width; 25.3 +- 0.25mm
3) If 2 measurements are added or subtracted, the absolute uncertainties are added.
EG; mass of rocket before launch = 420 +- 0.5g
Mass after launch = 106 +- 0.5g
Mass lost = 420-160 = 314 +- 1g
Percentage uncertainty
1) multiplying or dividing by a constant number doesn’t change percentage uncertainty.
EG: radius = 5mm+- 10%
Diameter = radius x 2= 10mm +- 10%
2) Unit conversion do not change percentage uncertainty
Eg: diameter = 10mm +-10%
Diameter = 1cm +- 10%
Diameter = 0.01 +- 10%
3) when multiplying or dividing 2 measured quantities, the percentage uncertainties are added.
Width = 25mm +- 10%
Length = 50mm +- 5%
Area = 25mm x 50mm = 1250mm^2 +- 15%
4) Raising a measurement to the power n multiples the percentage by n
Radius = 5mm +- 10%
Area= 3.14 x radius ^2
Area +79mm^2 +- 20%
