we're going to be looking at what variables are and also we'll look at how we can identify these variables for different experiments so let's first look at what exactly is a variable so when we are conducting an experiment the multiple so-called factors which are going to affect the outcome of an experiment generally when we are doing the experiment we are going to monitor these factors to see what their effect is on the outcome of the experiment these factors we can also call them as being variables and in the experiment there are usually three different types of variables that we want to identify that's the independent the dependent and the controlled variables so we just said that we are going to investigate a variable because they are going to influence the outcome of the experiment so an independent variable is the variable which we choose to investigate whereas the dependent variable is the variable that is going to change due to a change in our independent variable so here we'll look at an example of an investigation question that we might have so our question is how does the time spent hitting a beaker of water affect its temperature we investigate the effect of time that is spent healing the beaker of water since this is the variable that we are going to be investigating this is going to be our independent variable so that's the time that heat is applied and the effects that we're looking at is what the temperature is going to be of that water it's our dependent variable is going to be the final temperature of the water because the final temperature of the water is dependent on the time that the heat is applied we can look at another example what is the effect of time spent studying on test results so we're looking at the effect again of time however this time is time that's been studying and we are seeing what the effect is going to be on the test results so our independent variable will be time spent studying and we're looking at how time spent studying is going to affect test results so dependent variable is going to be test results controlled variables are variables that are kept constant during the investigation this means that all variables other than the independent and the independent variable should remain controlled and it's important to note that it is all variables except for those two this is done to ensure that our test is going to be fair and this is with regards to the validity of the experiment so in order to have a valid experiment you need to have controlled variables an example of a control variable would be ensuring that the same equipment is used if we're going to do multiple repetitions of the same type of test in order to compare variables let's look at how we can identify independent dependent and controlled variables here's our first example plant growth so first let's have a think about what variables affect plant growth well these include the volume of water which is used to water the plant the type of soil which the plant grows in the amount of sunlight exposure which the plant is going to receive and the temperature at which the plant is grown so we've just looked at the variables which affect plant growth it's important that only one independent variable is investigated at a time so we'll look at a revised question which we would be able to use to test through experimentation our question is going to be how does varying the amount of water given to a plant affect its growth rate first off we're looking at varying the amount of water so we're choosing a volume of water to be our independent variable and then we're looking how it affects growth rate so our dependent variable in this case might be that we're measuring the maximum height of plant after one month this is because the what height of the plan after one month is going to depend on the volume of water which was used to water the plant as discussed previously we are only going to investigate the effects of one variable at a time the variable which we chose was the volume of water because this variable was chosen as our independent variable all other variables must therefore be controlled these include the type of soil which the plant was grown in the amount of sunlight exposure and the temperature at which the plant was grown that means in this example where we have multiple different plants being grown with different volumes of water each must be the same plant they must have the same amount of soil they must have the same type of soil and they must be grown in the same temperature with the same exposure to sunlight so let's say that we've investigated the effects of water now we want to see what the effect of exposure of sunlight is going to be the dependent variable is still going to be the maximum height of the plant after one month because we are still going to be measuring the height of the plant after one month except this time the volume and the frequency of watering of the plant is going to be a controlled variable the type of flow is still going to be controlled in this case as well as a temperature at which the plant is grown here we'll look at a second example which is fish growth first again we can ask ourselves the question what are the different variables which affect fish growth variables include the type of fish feed which is used the amount or frequency of feeding the type of water which the fish is grown in the frequency of the water change and the temperature of the water inside the tank let's say that in this scenario we are going to be investigating the type of fish feed as our independent variable this means that we've chosen that variable out of the other ones to be independent the type of fish feed and what we are going to be measuring is the length of the fish after one month so that's our dependent variable which is going to depend on the type of fish feed which was used all our other variables are therefore going to become controlled variables that is the frequency of the feed temperature of water the type of water and the frequency of water change let's say now we wanted to choose a different variable as our independent variable we decide to choose the temperature of water now our question is what is the effect of temperature on fish growth our independent variable is the water temperature whereas the dependent variable is the length of the fish after one month our control variables will be the amount frequency and type of feed which was previously our independent variable also the type of water and the frequency of the water change