Variables in an experiment

A dependent variable is the outcome or response that is measured or observed during an investigation. It may change in response to the independent variable. Option A describes a controlled variable, which is kept constant. Exam tip: Look for the measured result or observed change to identify the dependent variable.

When investigating the effect of light, the duration or intensity of light is changed, so it is the independent variable. The amount of water must be the same for all plants because different amounts of water can also affect growth. Measured plant height is the dependent variable, or result. Exam tip: In a fair test, change only one factor and keep the others controlled.

Factors such as light, temperature and the plant’s water status can vary at different times of the day. This may introduce unwanted variation in measurements, making comparisons between days less reliable. The ruler does not change size; the issue is changing measurement conditions. Exam tip: For a fair comparison, measure plant height at the same time each day using the same method.

In option A, the experimenter deliberately changes the amount of water, so it is the independent variable. Seed germination or germination rate is the dependent variable because it may change in response to the water amount. In option B, temperature is the independent variable, and in option C, soil type is the independent variable. Exam tip: Identify the factor that is deliberately changed to find the independent variable.

Light duration is deliberately changed so it is the independent variable. Identify the factor that is changed.

Keeping the amount of water the same isolates the effect of light. A factor kept constant is a controlled variable.

Changing water amount may also affect growth so it becomes a confounding variable. Change only one main factor at a time.

In an experiment, the independent variable is the factor deliberately changed by the investigator. The dependent variable is the result observed or measured in response to that change. Other relevant factors should normally be kept constant so that the comparison is fair and the measured effect can be linked to the changed factor.

In this experiment, water temperature is varied, while the time required for sugar to dissolve is measured. Therefore, dissolving time is the dependent variable, because it is the observed outcome. Temperature is the independent variable. The amount of sugar and the container size would generally be controlled variables if the experiment is designed carefully. Hence option A is correct.

Water temperature is deliberately changed so it is the independent variable. The independent variable is the possible cause.

The amount of sugar and volume of water should remain the same. This allows a fair test of temperature.

A second changing factor makes the cause of the result unclear. This weakens the test of cause and effect.

Water amount is deliberately changed so it is the independent variable. Germination will be measured as the outcome.

Germination percentage is the measured outcome so it is the dependent variable. A percentage can be a quantitative outcome.

Using the same type of seed allows a proper comparison of the effect of water. Seed type is a controlled variable.

If seed type and water both change the cause of the result will be unclear. Choose one independent variable in a fair test.

In option A, the experimenter changes the type of soil and measures the average growth of the plants. Therefore, soil type is the independent variable and plant growth is the dependent variable. In option B, the amount of water—not soil type—is the independent variable. Exam tip: the factor deliberately changed in an experiment is the independent variable.

In this experiment, soil type is the factor that is changed, so it is the independent variable. Plant height gain is measured in response to the soil type; therefore, it is the dependent variable. Conditions such as water, light, and plant species should be kept the same as controlled variables. Exam tip: the result that is measured or observed is usually the dependent variable.

The daily amount of water should be the same for all plants. This makes the effect of soil type clear.

A confounding variable is an additional factor that changes along with the factor being studied and can also influence the measured result. Because its effect is mixed with the effect of the intended variable, the experiment cannot show clearly which factor caused the observed difference. Such a factor should be controlled whenever possible.

Here, the experiment compares plant growth in different kinds of soil, but the pots also have different sizes. Pot size can affect the amount of soil, water, root space, and possibly plant growth. Therefore, a growth difference might be caused by soil type, pot size, or both. Pot size is consequently a confounding variable, making option D correct. It is not a measurement unit or a dependent result.

In a fair comparison, the independent variable is the condition deliberately changed by the investigator. The dependent variable is the outcome measured, such as the time taken for a cloth to dry. Other relevant factors, including cloth type, size, starting wetness, and airflow, should be kept the same so that the comparison isolates the effect of the chosen condition.

Here, one cloth is placed in sunlight and another in shade, so the light condition is intentionally changed. It is therefore the independent variable. Drying time is the measured outcome and is the dependent variable. Cloth size and initial wetness should be controlled rather than changed. Hence option A is correct.

A dependent variable is the outcome that is measured or observed in an experiment. In this experiment, the time taken for the cloth to dry may change when sunlight or shade is changed, so drying time is the dependent variable. Sunlight or shade is the independent variable because it is deliberately varied. Exam tip: identify the quantity measured as the result to find the dependent variable.

In a fair comparison, only one factor, such as sunlight or shade, should be changed. Keeping the cloth size and initial wetness the same means that any difference in drying time can be attributed to the light condition. Drying time is the measured outcome, not a controlled variable, and a prediction is not an experimental variable. Exam tip: Factors kept unchanged are called controlled variables.

To compare the effect of sunlight and shade fairly, the cloths should be of the same size. A larger cloth may hold more water and have a different surface area, so it may take a different time to dry than a smaller cloth. Therefore, any difference in drying time cannot be attributed only to the light condition. Option A is incorrect because drying time is the dependent variable, while light condition is the independent variable. Exam tip: In a fair test, control all factors except the independent variable.

The surface area of the container is deliberately changed in this experiment, so it is the independent variable. The amount of water evaporated is the dependent variable because it is measured as the outcome. Factors such as the initial water volume and room temperature should be kept constant so that the result shows only the effect of surface area. Exam tip: the factor deliberately changed by the experimenter is the independent variable.

The amount of water evaporated after one hour is the outcome measured or observed in the experiment. Its value changes in response to a factor changed by the experimenter, such as time or temperature. Therefore, it is the dependent variable. An independent variable is the factor that is changed, not the measured result. Exam tip: A quantity measured as the result is usually the dependent variable.