Scientific Method Design

An example of a question that you might ask would be why do rainbows form?

Before beginning an investigation background research needs to be undertaken. Background research should always be referenced.

In this example the type of background research might include the particles found in the atmosphere, the diffraction of light through water and the different wavelengths of light.

You should write down a statement that answers your question. This is the hypothesis and should be specific, relating directly to the question they are asking.

In this example their hypothesis might be: Rainbows form because of the diffraction of light through water droplets in the atmosphere. If light is shone through water at the right angle a rainbow will form. Their hypothesis should be testable.

You should identify variables that are important in their specific experiment. For example, the temperature of the water, the type of light they use, the purity of the water, the angle of the light could all be variables in their experiment.

You should understand the difference between independent, dependent and controlled variables and be able to identify them in their experiment.

For example, the type of light might be controlled (sunlight). The temperature could be a independent variable (perform the experiment on different days with different temperatures). With the temperature as an independent variable then the angle the light comes out at could be a dependent variable, to see if there is a link. If the temperature is made a controlled variable on that day, then the angle could be the independent variable, and the shape and size of the rainbow would be the dependent variable.

You must design an experiment that accurately tests their hypothesis. The experiment is the most important part of the scientific method. These are all important concepts to know when designing an experiment:

1. The method should be written so that a complete stranger will be able to carry out the same procedure in the exact same way and get almost identical results.

2. The method must be clear and precise instructions including the labelling of apparatus, giving exact measurements or quantities of chemicals or substances to be used and making sure that all the apparatus used is listed.

3. The method must give clear instructions about/describing how the results should be recorded (table, graph, etc.)

4. The method should include safety precautions where possible.

You should present a one page experimental write up with an aim, the apparatus necessary, the method that will be followed. An example experiment is given here. Note that this is just an example, you could perform their experiment on anything.

1. Aim

   The aim of this experiment is to determine what happens when sunlight is shone through a glass of water.

2. Apparatus

   • A clear \(\text{500}\) \(\text{ml}\) glass, three A4 pieces of white paper, a tape measure, sticky tape, a pencil, a thermometer

   • At least \(\text{400}\) \(\text{ml}\) of water, sunlight.

3. Method

   • Use the sticky tape to stick an A4 piece of a paper to a sunny wall exactly \(\text{1}\) \(\text{m}\) from the ground.

   • Use the sticky tape to stick an A4 piece of paper above the first one, and the last A4 piece of paper below the first one.

   • Fill the glass with \(\text{400}\) \(\text{ml}\) water and measure the temperature (be careful to keep the thermometer out of direct sunlight between measuring the temperatures.

   • Hold the glass (near the bottom) level with the bottom of the middle piece of paper in the sunlight. If a rainbow forms on the sheets of paper, mark where it forms on the paper.

   • Measure the temperature of the water in the glass, then move the glass upwards \(\text{5}\) \(\text{cm}\) and repeat.

   • Repeat step \(\text{5}\) until you reach the top of the uppermost A4 piece of paper.

4. Results

   • Your results should be presented in the form of a table (Result? should be answered with a yes or a no depending on whether a rainbow formed):

     Temperature (\(^{\circ}\)C)	Height of glass (m)	Result?	Height of rainbow

     From this data the angle of refraction of the water can be measured, as well as what angle is required for the sunlight to create a rainbow through the water.