AQA Physics A-Level Measurements and Errors

AQA Physics A-Level Section 1: Measurements and their Errors Flashcards

SI Units

Fundamental units in the SI system, including mass (kg), length (m), time (s), amount of substance (mol), temperature (K), and electric current (A).

Derived SI Units

Can be derived using equations by multiplying or dividing the respective SI units of the quantities involved, e.g., Force (F) = mass (m) x acceleration (a).

SI Unit Prefixes

Tera (T) - 10^12, Giga (G) - 10^9, Mega (M) - 10^6, Kilo (k) - 10^3, Centi (c) - 10^-2, Milli (m) - 10^-3, Micro (µ) - 10^-6, Nano (n) - 10^-9, Pico (p) - 10^-12, Femto (f) - 10^-15

MeV to Joules Conversion

Multiply by 1.6 x 10^-19

kWh to Joules Conversion

1 kWh = 3.6 x 10^6 J

Random Errors

Affect precision, causing a spread of measurements around the mean. Cannot be completely eliminated.

Reducing Random Errors

Take at least 3 repeats and calculate a mean, use computers/data loggers/cameras to reduce human error, use appropriate equipment with higher resolution.

Systematic Errors

Affect accuracy, causing all results to be too high or too low by the same amount each time.

Reducing Systematic Errors

Calibrate apparatus, correct for background radiation, read the meniscus at eye level.

Precision

Consistent measurements that fluctuate slightly about a mean value.

Repeatability

The ability of the original experimenter to redo the experiment with the same equipment and method and obtain the same results.

Reproducibility

The ability to reproduce the experiment by a different person or with different techniques and equipment and still obtain the same results.

Resolution

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

Accuracy

A measurement close to the true value.

Uncertainty

The bounds within which the accurate value can be expected to lie.

Absolute Uncertainty

Uncertainty given as a fixed quantity, e.g., ± 0.6 V

Fractional Uncertainty

Uncertainty as a fraction of the measurement.

Percentage Uncertainty

Uncertainty as a percentage of the measurement.

Uncertainty in a Reading

± half the smallest division.

Uncertainty in a Measurement

At least ±1 smallest division.

Uncertainty for Repeated Data

Mean ± range/2

Combining Uncertainties: Adding/Subtracting Data

Add absolute uncertainties.

Combining Uncertainties: Multiplying/Dividing Data

Add percentage uncertainties.

Combining Uncertainties: Raising to a Power

Multiply percentage uncertainty by the power.

Uncertainties on Graphs

Shown as error bars on graphs.

Orders of Magnitude

Power of ten which describes the size of an object

Estimation

A skill physicists must use to approximate the values of physical quantities.