Measurements and their errors Flashcards
What are the six SI units?
mass (m)- Kg
length (l) - m (metres)
Time (t) - s (seconds)
Amount of substance(n) - mol (moles)
Temperature (t) - K (kelvin)
Electric current (I) - A (amperes)
How can SI unit quantities be derived?
By there equation. e.g. F= ma = Kg*ms^-2 so N = Kgms^2
What is the multiplier of Tera(T)
*10^12
What is the multiplier of Giga(G)
*10^9
What is the multiplier of Mega(M)
*10^6
What is the multiplier of Kilo(K)
*10^3
What is the multiplier of centi(c)
*10^-2
What is the multiplier of milli(m)
*10^-3
What is the multiplier of micro(µ)
*10^-6
What is the multiplier of Nano(n)
*10^-9
What is the multiplier of pico(p)
*10^-12
What is the multiplier of Femto(f)
*10^-15
What does 1eV equal in joules?
1.6x10^-19J
How do u convert from eV to J
times by 1.6x10^-19
How do u convert from J to eV
divide by 1.6x10^-19
what is 1 KW in Js^-1?
1000 Js^-1
How do you convert 1 KWh to J?
do 1000*3600 = 3.6x10^6 because 1 kwh is 1000js^-1 and 1 hour is 3600 seconds.
What do random errors affect?
precision
What three things can you do to reduce random errors?
- Take at least three repeats and calculate a mean this allows anomalies to be identified
- Use computers/data logger/cameras to reduce human error and enable smaller intervals
- Use appropriate equipment, for example a micrometre has a higher resolution (0.1mm) than a ruler(1 mm)
What do systematic errors affect?
accuracy
What three ways reduce systematic errors?
- calibrate apparatus by measuring a know value, if reading is inaccurate then their is a systematic error
- In radiation experiments correct for background radiation by measuring it before hand and excluding it from final results
-Read meniscus at eye level (to reduce parallax error) and use controls in experiments
define precision
Precise measurements are consistent, they fluctuate slightly about the mean value - this doesn’t indicate the value is accurate
define repeatability
If the original experimenter can redo the experiment with the same equipment and method then get the same results its repeatable.
define reproducibility
If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is reproducible
define resolution
The smallest change in the quantity being measured that gives a recognisable change in reading
define accuracy
A measurement close to the true value is accurate
What is the uncertainty of a measurement?
Is the bounds within which the true value can be expected to lie.
What is absolute uncertainty?
Uncertainty is given as a fixed quantity e.g. 7±0.6 V
What is fractional uncertainty?
Uncertainty as a fraction of the measurement e.g. 7±3/35 V
What is percentage uncertainty?
Uncertainty as a percentage measurement e.g. 7±8.6%
How can you reduce percentage and fractional uncertainties?
measure larger quantities
What is a reading?
when one value is found
What is a measurement?
When the difference between 2 readings is found.
What is the uncertainty in a reading?
± half the smallest division
What is the uncertainty in a measurement?
at least ± smallest division
