3.1 Measurements and their errors Flashcards
What is the SI unit of mass?
Kg
What is the SI unit of time?
s
What is the SI unit of temperature?
K (Kelvin)
What is the SI unit of current?
A (Amperes)
What is the SI unit of distance?
m
What is the SI unit of quantity of matter?
mol
What is the prefix for the magnitude 10^12?
T (tera)
What is the prefix for the magnitude 10^9?
G (giga)
What is the prefix for the magnitude 10^6?
M (mega)
What is the prefix for the magnitude 10^3?
k (kilo)
What is the prefix for the magnitude 10^-2?
c (centi)
What is the prefix for the magnitude 10^-3?
m (milli)
What is the prefix for the magnitude 10^-6?
µ (micro)
What is the prefix for the magnitude 10^-9?
n (nano)
What is the prefix for the magnitude 10^-12?
p (pico)
What is the prefix for the magnitude 10^-15?
f (femto)
How do you convert J to eV?
Divide by e (1.60x10^-19)
How do you convert from J to kWh?
Divide by 3.6x10^6
What are random errors?
Errors that affect precision, causing differences in measurements causing a spread around the mean
How do you reduce random errors?
- Take at least 3 repeats and calculate a mean - can also allow anomalies to be identified and removed respectively
- Use computers/data loggers/cameras to reduce human error and enable smaller intervals
- Use appropriate equipment - e.g. a micrometer has a higher resolution (0.1mm) than a ruler (1mm)
What are systematic errors?
Errors that affect accuracy - occur due to apparatus or faults in the experimental method, causing all results to be too high or too low by the same amount each time
E.g. balance isn’t zeroed properly (zero error) or reading scale at a different angle (parallax error)
How do you reduce systematic errors?
- Calibrate apparatus by measuring a known value (e.g. weight 1kg mass on a mass balance), if reading is inaccurate then systematic error is easily identified
- In radiation experiments correct for background radiation by measuring it beforehand and excluding it from final results
- Read the meniscus (central curve on the surface of a liquid) at eye level (to reduce parallax error) and use controls in experiments
What is precision?
How consistent measurements are and if they fluctuate slightly about a mean (doesn’t indicate accuracy)
What is repeatability?
When the original experimenter can redo the experiment with the same equipment and method and get the same results
What is reproducibility?
When the experiment is redone by a different person or with different techniques and equipment and the same results are found
What is resolution?
The smallest change in the quantity being measured that gives a recognisable change in reading
What is accuracy?
How close a measurement is to the true value
What is the uncertainty in a reading?
± half the smallest division
What is the uncertainty in a measurement?
At least ± one smallest division
What is the uncertainty for repeated data?
Mean ± range/2
What number of sig figs should uncertainties have?
The same as the data
How do you combine uncertainties when adding/subtracting data?
Add absolute uncertainties
How do you combine uncertainties when multiplying/dividing data?
Add percentage uncertainties
How do you combine uncertainties when raising to a power?
Multiply percentage uncertainty by power
