Working as a Physicist Flashcards
SI Units: Current
Ampere (A)
SI Units: Temperature
Kelvin (K)
SI Units: Amount of substance
Mole (mol)
SI Units: Intensity
Candela (cd)
Tera Giga Mega Kilo Centi Milli Micro Nano Pico Femto
10^12 10^9 10^6 10^3 10^-2 10^-3 10^-6 10^-9 10^-12 10^-15
What are random errors
Random error affects precision, causes differences in measurements which causes a spread about the mean or a line of best fit on a graph
How to reduce random errors
Take 3 repeats and find a mean to reduce random error and eliminate anomalies
Use computers, data loggers, cameras to reduce human error and enable smaller intervals - increasing precision
Use appropriate meter e.g. for small measurements use a Vernier caliper which has a lower resolution than a ruler making it more accurate
What are Systematic errors
Systemic errors affect accuracy and occur due to the apparatus or faults in the experimental method. Systematic errors causer all results to be too high or too low by the same amount each time, systemic errors usually cause an intercept on the y-axis
e.g. zero error - scale does not reduce to zero even though it has no mass on it
How to reduce systematic error
Calibrate apparatus by measuring a known value e.g. weigh 1kg on a mass balance. If the reading is inaccurate then the 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 (the central curve on the surface of a liquid) at eye level ( to reduce parallax error and use controls in experiments
Uncertainty
The interval in which the true value of a measurement can be considered to lie with a given level of confidence or probability
Any measurement will have some uncertainty about the result, which will have originated from variation in the data obtained and be subjected to random or systematic effects
Calculating uncertainty
For single readings
Uncertainty = resolution/2
For multiple readings:
Use resolution/2 when its bigger then half the range of the values
Use range/2 when its bigger than resolution/2
Resolution
The smallest measuring interval and the source of uncertainty in a single reading
For digital: res = the min. scale
For analogue: res = marked increment
Combing uncertainties
When adding/subtracting data - add absolute uncertainties
When multiplying/dividing - add percentage uncertainties
When raising to a power - Multiply percentage uncertainty by power
