Unit 1 Measurements and their Errors

What are SI units?

The standard units of measurement used in scientific contexts, including kilograms for mass, meters for length, seconds for time, and others.

What is precision?

Precise measurements are consistent, with slight fluctuations around a mean value, indicating reliability but not necessarily accuracy.

What are random errors?

Errors in measurements that cause a spread around the mean, often due to unpredictable factors like electronic noise.

What are systematic errors?

Errors that affect accuracy and consistently skew results in one direction due to faults in the method or equipment.

What is resolution?

The smallest change in the quantity being measured that can be observed, affecting the instrument's uncertainty.

What is absolute uncertainty?

Uncertainty expressed as a fixed quantity, for example, ±0.5V.

What is fractional uncertainty?

Uncertainty represented as a fraction of the measurement, for example, ±0.3/7V.

What is percentage uncertainty?

Uncertainty expressed as a percentage of the measurement, for example, ±8.6% of 7V.

What is reproducibility?

The ability to obtain the same results when an experiment is repeated by different people or using different methods.

What are orders of magnitude?

Powers of ten that describe the size of an object and can be used to compare the sizes of different objects.

What is calibration?

The process of checking and adjusting the accuracy of an instrument by measuring a known value.

What is the meniscus?

The curve at the surface of a liquid in a container, which is used to accurately read the measurement at eye level.

What are error bars?

Graphical representations of the variability of data, used to indicate the uncertainty of a measurement.

What is estimation?

The process of approximating physical quantities to reasonable values for comparisons or validations.

What is the SI unit of mass?

Kg (kilograms)

What is SI unit of length?

m (metres)

What is SI unit of time?

s (second)

What is the SI unit of electric current?

A (amperes)

What is the SI unit of temperature?

K (kelvin)

What is the SI unit for the amount of substance?

mol (moles)

What is the derived SI unit of force?

N (Newton) equivalent to kg·m/s².

What is eV (electron volt)?

A unit of energy commonly used in atomic and particle physics.

What are kWh (kilowatt hours)?

A unit of energy equivalent to one kilowatt of power used for one hour.

How can random errors be reduced?

Take at least 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 because it has a higher resolution than a ruler

What are the prefixes and powers from highest to lowest?

Tera = 12, Giga = 9, Mega = 6, Kilo = 3, Centi = -2, Milli = -3, Micro = -6, Nano = -9, Pico = -12, Femto = -15

How can systematic errors be reduced?

Calibrate apparatus by measuring a known value so that 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 the final results

Read the meniscus at eye level and use controls in experiments

What is the difference between readings and measurements?

Readings are when one value is found whereas measurements are when the difference between two readings is found

What is the uncertainty in an analog reading?

± half the smallest division

What is the uncertainty in an analog measurement?

± at least 1 smallest division

What is the uncertainty of digital readings?

± the last significant digit but the resolution of an instrument also affects its uncertainty

What is the uncertainty for repeated data?

Half the range show as mean ± range/2

How should the uncertainties be combined when adding/subtracting data?

Add absolute uncertainties

How should the uncertainties be combined when multiplying/dividing data?

Add percentage uncertainties

How should the uncertainties be combined when raising to a power?

Multiply percentage uncertainty by power

What to do when asked to give a value to the nearest order of magnitude?

Calculate the value as a power of 10