1.3 Errors and uncertainties

Define systematic error.

A consistent error that affects accuracy, caused by faults in apparatus or method, making all measurements too high or too low by the same amount each time.

Define random error.

An error that affects precision, causing unpredictable variations about the mean value; cannot be eliminated completely.

State one example of a systematic error.

Balance not zeroed correctly.

State one example of a random error.

Electronic noise in an instrument.

Describe how to reduce systematic error.

Calibrate apparatus using a known value.

Describe how to reduce random error.

Take repeated measurements and calculate a mean.

Define precision.

The closeness of repeated measurements to each other.

Define accuracy.

A measurement close to the true value.

Define uncertainty.

The bounds in which the accurate value can be expected.

Define absolute uncertainty.

The uncertainty expressed in the same units as the measured value.

State the rule for adding/subtracting absolute uncertainties.

Add the individual absolute uncertainties:
∆ x = ∆ a + ∆ b.

Define percentage uncertainty.

The uncertainty expressed as a percentage (fraction) of the measured value.

State the rule for multiplying/dividing percentage uncertainties.

Add the percentage uncertainties of each quantity:

total % uncertainty = sum of the % uncertainties.

State the rule for powers in uncertainty.

Multiply the percentage uncertainty by the power:

%∆Q = n x %∆ (measurement).