# Measurements

#### Chapter 1 - Measurements

Learn about physical quantities, and the difference between base quantities and derived quantities. We list the six base quantities and their SI units required in the GCE A Levels, and we also give a couple of examples of derived quantities and how they are formed from the base quantities.

In the GCE A Levels, we have to be able to express all derived units within the syllabus in terms of their base units. We will discuss how this is done in this video.

Understand what it takes for an equation in physics to be considered as homogeneous. It is also a GCE A Level requirement to check the homogeneity of equations by comparing the base units of the various quantities in the equation.

A prefix is attached at the start of a unit, to scale that unit by some power of ten. In the GCE A Levels, we are required to know a number of prefixes, and these will be introduced in this video.

In the GCE A Levels, we split physical quantities into scalar quantities and vector quantities. In this short video we will describe what differentiates scalar and vector quantities and give some examples of each.

Resolving vectors in the GCE A Levels involves splitting the vector into two components which are perpendicular to each other. We will discuss a systematic way to always resolve vectors correctly.

One method to add and subtract vectors in the GCE A Levels is to use vector diagrams. This video will show how this is done, simply by drawing a vector triangle, and using some simple trigonometry (cosine rule and sine rule) to evaluate the resultant vector’s magnitude and direction.

In the GCE A Levels, you may be required to add more than two vectors together, in which case the vector diagram method may not work. We introduce an alternative method of adding vectors, by resolving all the vectors first, finding a two net vectors in to two perpendicular components, and combining these components to find the magnitude and direction of the resultant vector.

The two main types of experimental errors in the GCE A Levels are systematic errors and random errors. Systematic errors are consistent deviations from the true value while random errors are unpredictable scatters about the mean. This video will discuss these errors including their common causes and some suggestions to reduce them.

The GCE A Levels requires us to define the terms accuracy and precision. We will give a brief description of each and how they link to systematic and random errors.

Some questions in the GCE A Levels will involve measurements with their associated uncertainties. We introduce the idea of uncertainties in measurements, and specifically, the absolute and fractional uncertainty.

When we add or subtract quantities with their uncertainties in the GCE A Levels, we always add the absolute uncertainties together. This video will discuss this and demonstrate this with a numerical example.

When we multiply or divide quantities with their uncertainties in the GCE A Levels, we always add the fractional uncertainties together. This video will discuss this and demonstrate this with a numerical example.

Certain expressions in the GCE A Levels may have the same measured value in both the numerator and denominator. In such a situation, we must use the foundational method to evaluate this expression together with its associated uncertainty.