Fair Testing Past Paper PDF

## Fair Testing ### Why are Fair Tests Carried Out? A **variable** is any factor that can change and have different values. In an experiment you are usually interested in two variables: * The **independent variable**, for which you choose the values. * The **dependent variable**, which varies...

## Fair Testing ### Why are Fair Tests Carried Out? A **variable** is any factor that can change and have different values. In an experiment you are usually interested in two variables: * The **independent variable**, for which you choose the values. * The **dependent variable**, which varies as the independent variable changes and is the variable you are measuring. 1. In the experiment shown in photo A, which is the independent variable and which is the dependent variable? Explain your answer. *** **Photo A description**: This Image shows an experimental setup with a digital timer and two transparent cups, each placed over what appear to be fuel sources (possibly tea lights or small candles) on a white surface. The timer displays measurements with labels underneath it saying 'minutes', 'seconds', and fractions of a 'second'. There's also some handwritten notes beside the items. *** **Answer**: Two variables in this experiment are the volume of fuel burned and the time it takes for all the fuel to burn. *** In many experiments, you want to test the effect of a single variable on another. You want to find out how the independent variable affects the dependent variable. So, you do not want any other variables affecting the dependent variable. It is important to control these other variables as far as possible, and so they are called **control variables**. Controlling variables is also very important in industry. MMT is a substance added to petrol to reduce pollution. Scientists found the best way of making MMT by changing the amount of one reactant and measuring how much MMT was produced. They also discovered that it was important to control the temperature during this reaction. In 2007, in Florida, USA, something went wrong with an MMT factory cooling system. The temperature rise caused an explosion that spread debris up to a mile away. 1. Look at photo A. * a) One variable that should be controlled is the type of fuel. Explain how using different fuels might affect the dependent variable. * b) Describe one other variable that should be controlled in this experiment and what effect it might have if it were not controlled properly. 2. In the experiments to find the best way to make MMT: * a) which was the independent variable? * b) which was the dependent variable? * c) which variable was not controlled properly and caused the explosion? **Photo B description**: This Image shows the aftermath of an industrial explosion at what is labeled 'the remains of the MMT laboratory'. The scene depicts significant destruction with twisted metal wreckage and scattered debris suggesting significant structural damage. *** ## Planning a fair test A fair test is an experiment in which all the control variables are controlled. This means that these variables do not change, and so cannot affect the dependent variable. Fair tests produce valid data. Something that is valid does what it is supposed to do. By controlling all other variables, data from a fair test only shows the effect of the independent variable on the dependent variable. When you plan an experiment, you first identify the independent and dependent variables. Then you must identify all the other variables that could affect the dependent variable. Finally, you need to plan how to control these other variables. The Method below describes how to carry out an experiment using the equipment in photo C. ### Method **Photo C description**: This image shows a setup with two tea lights: one placed directly on a heat-resistant mat, and another elevated on a block also covered with a heat-resistant mat. Each tea light is covered with a transparent, heat-resistant glass container. The scene is dimly lit allowing the glow from the tea lights to be visible. A note reminds the viewer to 'Wear eye protection when carrying out this experiment!'. * **A** Place one tea light on a heat-resistant mat and another tea light on a block on a heat-resistant mat. * **B** Measure the height between the surface and the base of the wick of both tea lights and record the values. * **C** Light both tea lights and cover them both immediately with heat-resistant glass containers. Start the stopwatch. * **D** Measure the time taken for each flame to go out and record the values. You usually record results from experiments in a table (see table D). It is a convention that the independent variable goes in the left-hand column. 1. Identify the independent and dependent variables in the experiment described in the Method above. 2. Use your answer to question 4 to state the question this experiment is set up to answer. 3. * a) Suggest two other variables that could affect the dependent variable. * b) Explain your answer to part a. * c) Describe how you could control each of the variables you identified in part a, in order to collect valid data. Table D: | Height of wick (cm) | Length of time it burned (s) | | :------------------ | :----------------------------- | | 1 | | | 2 | | | 3 | | | 4 | | I can... * identify control variables in an experiment and describe how to control them. * explain why it is important to carry out a fair test.