Designing experiments 

In a nutshell

Every experiment is unique, so making sure to take the right steps when setting them up is important. Research into the topic is important so that you know what kind of experiment you are setting up. This includes identifying the variables being measured or changed, as well as what needs to be controlled.

Definitions

These are key words that you will be expected to know the meaning of when planning and setting up experiments.

Variables

There are three types of variables to consider when setting up an experiment. 

Independent variables

The independent variable is the variable that is being changed during the experiment. This variable usually doesn't depend on anything else and is varied to observe what effect it has on something else. 

Example

What is the independent variable when investigating how the thickness of a wire affects its resistance?

The variable being changed is the thickness of a while. Therefore, the thickness of a wire is the independent variable.

Dependent variables

The dependent variable is the variable being measured during the experiment. It usually depends on the independent variable, which means it will change when the independent variable is changed.

Example

What is the dependent variable when investigating how the thickness of a wire affects its resistance?

The variable being measured is the resistance of the wire. Therefore, the resistance is the dependent variable.

Control variables

Finally, control variables are all the variables that are kept the same throughout the experiment. Keeping them constant is important, because if they are not kept constant then they could have unintended effects on the dependent variable.

Example

What is the control variable when investigating how the thickness of a wire affects its resistance?

One of the variables which is being controlled is the temperature of the wire. If the temperature of the wire is not controlled, this could affect the dependent variable.

Accuracy and precision

Accuracy and precision are ways to describe how reliable an experiment is and steps should be taken to increase both properties as much as possible.

Accuracy

Accuracy represents how close the measured values are to the true value. Accuracy is affected by the instrument used, and can be improved by using instruments with a higher sensitivity and lower error. 

Accuracy can also be affected by systematic errors, which are errors that consistently differ from the true value in the same way. 

Precision

Precision represents how close measured values are to each other. It is affected by random errors, which means that doing an experiment less will result in a larger chance the values will have substantial random error.

Precision is increased by repeating the experiment, as this decreases the chances that all the readings will have a large random error.

A Accuracy B Precision

In A, the darts are very close or on top of the bullseye. This means these darts are very close to the target. Therefore, the results are accurate. In B, the darts are further away from the bullseye. However, they are all close to each other. This means, this is the area the darts will land. The results are precise as they're all next to each other.