skills

• prefixes in order:

  femto, pico, nano, micro, milli, centi, deci, kilo, mega, giga, tera
• to convert from eV to J, multiply by 1.6e-19

  to convert from J to eV, divide by 1.6e-19
• random errors affect precision, causing spread about the mean, you cannot get rid of all random errors
• ways to reduce random error:

  • take multiple repeat measurements and calculate a mean, remove anomalies
  • use computers or data loggers to reduce human error
  • use equipment with the highest resolution possible
• systematic errors affect accuracy, causing all results to be too high or too low by the same amount, you can remove all systematic errors
• ways to reduce systematic errors:

  • calibrate apparatus using an object of known value
  • if working with radiation, find the background radiation and remove this from the final result
  • always read from the bottom of the meniscus at eye level
  • use controls where possible
• precision = values which are consistent about a mean, with slight fluctuation
• repeatability = the ability of the same person to repeat the experiment with the same equipment and method and get the same result
• reproducibility = the ability of a different person to repeat the experiment with different equipment or method and get the same result
• resolution = the smallest change in the quantity being measured that gives a recognisable change in reading
• accuracy = measurements close to the true value
• uncertainty = upper and lower bounds in which you would expect to find the value
• absolute uncertainty is given as a fixed quantity
• fractional uncertainty is given as a fraction of the measurement
• percentage uncertainty is given as a percentage of the measurement
• to reduce percentage and fractional uncertainties, measure larger quantities of the thing
• readings are when one value is found, measurements are when the difference between two readings is found
• uncertainty in a reading is plus or minus half the smallest division
• uncertainty in a measurement is the sum of the uncertainties in the readings which make it up
• uncertainty in digital readings is either given or assumed to be plus or minus the smallest possible reading
• to reduce uncertainty in a ruler, fix one end of it as this reduces the number of measurements required
• uncertainties should be given to the same number of significant figures as the data
• when adding or subtracting data, add the absolute uncertainties
• when multiplying or dividing data, add the percentage uncertainties
• when raising data to a power, multiply the percentage uncertainty by the power
• uncertainties can be shown on graphs using error bars
• a line of best fit or a line of worst fit needs to go through all the error bars on the graph
• to find the uncertainty in a gradient, draw two lines of worst fit, a steep one and a shallow one, calculate the gradients of each, the uncertainty is the difference between these