Practical Skills

19 flashcards · Physics · by Ella Corcoran

  1. Precision

    Precise measurements are consistent, they fluctuate slightly about a mean value - this doesn’t indicate the value is accurate

  2. Repeatability

    If the original experimenter can redo the experiment with the same equipment and method then get the same results it is repeatable

  3. 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

  4. Resolution

    The smallest change in the quantity being measured that gives a recognisable change in reading

  5. Accuracy

    A measurement close to the true value is accurate

  6. Systematic errors affect

    accuracy

  7. Systematic errors occur due to

    the apparatus or faults in the experimental method. Systematic errors cause all results to be too high or too low by the same amount each time.

  8. To reduce systematic error:

    calibrate apparatus by measuring a known value (e.g. weigh 1 kg 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

  9. Random errors affect

    precision

  10. To reduce random errors:

    Take at least 3 repeats and calculate a mean, this method also allows anomalies to be identified Use computers/data loggers/cameras to reduce human error and enable smaller intervals Use appropriate equipment, e.g a micrometer has higher resolution (0.1 mm) than a ruler (1 mm)

  11. Absolute uncertainty

    The uncertainty in a reading ± half the smallest division, e.g. for a thermometer the smallest division is 1°C so the uncertainty is ±0.5°C uncertainty in a measurement is at least ±1 smallest division, e.g. a ruler, must include both the uncertainty for the start and end value, as each end has ±0.5mm, they are added so the uncertainty in the measurement is ±1mm Digital readings and given values will either have the uncertainty quoted or assumed to be ± the last significant digit e.g. 3.2 ± 0.1…

  12. You can reduce uncertainty by

    measuring multiple instances fixing one end of a ruler as only the uncertainty in one reading is included

  13. Combining uncertainties

    Adding / subtracting data- ADD ABSOLUTE UNCERTAINTIES Multiplying/dividing data- ADD PERCENTAGE UNCERTAINTIES Raising to a power- MULTIPLY PERCENTAGE UNCERTAINTY BY POWER

  14. The absolute uncertainty in a gradient on a graph

    Draw a steepest and shallowest line of worst fit, it must go through all the error bars Calculate the gradient of the best and worst line , the uncertainty is the difference between the best and worst gradient

  15. The percentage uncertainty in a gradient on a graph

    {[mod(best gradient-worst gradient)]/best gradient} x 100 or {[mod(best y intercept-worst y intercept)]/best y intercept} x 100

  16. Discrete

    only certain values can be taken, e.g. number of objects Display on scatter graphs and bar charts

  17. Continuous

    can take any value on a scale e.g. current in a circuit. Display on line or scatter graph

  18. Categoric

    values that can be sorted into categories e.g. types of material Display on a pie or bar chart

  19. Ordered

    data that can be put in ordered categories e.g. low, medium,high Bar charts can display ordered data