# Physics (A-level)/Practical skills in physics

## Overview

For A-level physics, you will have to partake in certain practical experiments of three types: quantitative, qualitative and evaluative. You will be graded for one of each in both you AS and A2 parts of the course, adding up to six graded experiments in the two years. You will usually have two or three attempts at each category.

## Evaluative

You will be asked to evaluate data from an experiment you have done using the examiners results.

You will need to comment on an experiments precision, reliability and accuracy. For this you will need to understand the difference between the three.
Precision - this refers to the distance of the points from the line of best fit on the graph. If the majority of the points lye on or very near to the line of best fit, the experiment is said to be precise.
Reliability - this refers to the difference in results between repeats. If a repeat has a very similar value in the experiment, the experiment is said to be reliable.
Accuracy - this refers to the comparison of a calculated value to the accepted value. If a value that you calculate is very close to the accepted value, it is said to be accurate. An example of this would be if you calculated the earths gravitational field strength (g) to be 9.75ms-2, it is very close to the accepted value of 9.81ms-2. Therefore that experiment would be accurate.

Another evaluation you must make is working out or comparing gradients and y-intercepts. For this you must know the equation
y=mx+C
where y and x are variables, m is the gradient and C is the y-intercept.
All linear equations can be rearranged into this form, in order to work out certain values.
For example the equation,
m=PM(1/l)+M
The equation in this example compares m over 1/l. Comparing this to y=mx+C, m is the y-variable, 1/l is the x-variable, PM is the gradient and M is the y-intercept. You will be given or will have to work out the graph's gradient and y-intercept. With these you can work out values for P and M.