Variables in an experiment

Correct answer: C. Controlled variable

Because the container size is kept the same in every trial, it is a controlled variable. Controlled variables are held constant so that the effect of changing the independent variable can be observed fairly. An independent variable is deliberately changed, but the container size is not changed here. Exam tip: A quantity described as “kept the same” or “constant” is usually a controlled variable.

Correct answer: D. Container size may affect the result

Changing the container size can alter conditions such as surface area, capacity, or heat transfer. Therefore, it may affect the result, so it should be kept constant as a controlled variable in a fair test. Option B is incorrect because changing container size does not ensure that the independent variable remains unchanged. Exam tip: In a fair test, keep all factors other than the independent variable constant.

Correct answer: A. How does light duration affect the number of leaves?

An independent variable is the factor deliberately changed in an experiment. In option A, the duration of light is changed and its effect on the number of leaves is observed; therefore, light duration is the independent variable. In option B, the number of leaves is treated as the cause, so it does not represent the intended experimental relationship. Exam tip: Ask, “What is being changed?” to identify the independent variable.

Correct answer: B. How long does cloth take to dry in sunlight and shade?

In option B, sunlight and shade are the conditions being changed, while the time taken by the cloth to dry is measured. Therefore, drying time is the dependent variable. In option D, the measured outcome is water absorbed, not drying time. Exam tip: The result that is measured or recorded in an experiment is usually the dependent variable.

Correct answer: C. The same

The cloth size should be kept the same in every trial. Changing its size can change the amount of water in the cloth and the surface area available for drying, so sunlight and shade cannot be compared fairly. Choosing the largest cloth is not necessary; controlling the size is what matters. Exam tip: In a fair test, keep all factors other than the one being tested constant.

Correct answer: D. Independent variable

The independent variable is the factor whose value the experimenter deliberately sets or changes to study its effect. The dependent variable is the measured response, while controlled variables are kept constant. Exam tip: the variable that is changed is the independent variable.

Correct answer: A. Dependent variable

The dependent variable is the outcome that is measured or observed in an experiment. Its value may change when the independent variable is changed, so option A is correct. A controlled variable is kept the same so that other factors do not affect the result. Exam tip: the independent variable is changed, while the dependent variable is measured.

Correct answer: B. Controlled variables

Controlled variables are factors kept the same throughout an experiment, so they are not deliberately changed. This ensures that any change in the result is due only to the independent variable. The independent variable is changed, while the dependent variable is measured for its effect. Exam tip: If a factor is kept constant, it is a controlled variable.

Correct answer: C. Type of soil

An independent variable is the factor deliberately changed by the experimenter. Here, the student uses different types of soil, so soil type is the independent variable. Plant growth or plant height is a measured outcome, so it is a dependent variable. Exam tip: identify the factor that is changed deliberately.

Correct answer: D. The same measured amount in every pot

The water amount should be the same and measured for every pot. This keeps water as a controlled variable, so any difference in plant growth can be linked to the type of soil. If different amounts of water are used, the effects of soil and water become mixed. Exam tip: In a fair test, change only the variable being investigated and keep the others constant.

Correct answer: A. Measuring the time taken for sugar to dissolve while stirring at different speeds

In option A, the experimenter deliberately changes the stirring speed and measures the time taken by sugar to dissolve. Thus, stirring speed is the independent variable, while dissolving time is the dependent variable. In option B, the independent variable is water temperature, not stirring speed. Exam tip: The factor deliberately changed in an experiment is the independent variable.

Correct answer: B. The same in each trial

To investigate the effect of stirring speed, water temperature must be a controlled variable, so it should remain the same in every trial. If temperature changes, the result may be affected by both temperature and stirring speed. Exam tip: In a fair test, change only the independent variable and keep other important factors constant.

Correct answer: C. Plant growth

A dependent variable is the outcome that is measured or observed in an experiment. Here, sound intensity is deliberately changed, so it is the independent variable, while plant growth is measured. Therefore, plant growth is the dependent variable. Factors such as the amount of water and pot size should be kept controlled for a fair test. Exam tip: the variable that is measured is usually the dependent variable.

Correct answer: D. Independent variable

In this experiment, sound intensity is deliberately varied, so it is the independent variable. The dependent variable is the outcome that is measured or observed when sound intensity changes. Exam tip: identify the factor deliberately changed by the experimenter as the independent variable.

Correct answer: A. One variable changes and other relevant variables remain the same

In a fair experiment, only the independent variable is changed while other relevant variables are controlled, or kept the same. Therefore, any difference in the result can be linked to the variable being tested. If all variables change together, the cause of the result cannot be identified. Exam tip: remember, change one variable and control the rest for a fair test.

Correct answer: B. The investigation plan becomes clear

Identifying variables helps distinguish the independent variable, dependent variable, and controlled variables. It makes clear which factor should be changed, which result should be measured, and which conditions must be kept constant; therefore, the investigation plan becomes clear. A conclusion is not decided in advance—it is drawn from experimental data. Exam tip: In a fair test, change only the independent variable at a time.

Correct answer: C. Changed temperature as independent variable

A deliberately changed temperature is an independent variable. Identify whether a factor is changed measured or kept the same.

Correct answer: D. Measured time as controlled variable

Direct answer: Option D is correct because it gives an incorrect role. A variable deliberately changed by the investigator is independent; a measured outcome is dependent; a condition held constant is controlled. Option A is correct matching: changed light is the independent variable. Option B is correct matching: measured height is the dependent result. Option C is correct matching if the same water amount is maintained throughout; it is then a controlled variable. Option D is incorrect because measured time is an outcome, so it should be a dependent variable, not a controlled variable. The word “measured” is an important clue: it usually points to the result being observed. A controlled variable is not the result being measured; it is a condition kept unchanged to make comparison fair. Memory cue: change it = independent, measure it = dependent, hold it constant = controlled.

Correct answer: A. How does water temperature affect the time taken for salt to dissolve?

An independent variable is the factor that the experimenter deliberately changes. In option A, the water temperature is changed and the time taken for salt to dissolve is measured, so water temperature is the independent variable. In options B, C and D, the independent variables are the amount of salt, amount of water and stirring speed respectively. Exam tip: In a question asking “How does X affect Y?”, X is usually the independent variable.

Correct answer: B. How long does water take to evaporate at different temperatures?

In option B, temperature is changed, so it is the independent variable. The time taken by water to evaporate is measured, so it is the dependent variable. In option A, the dependent variable is the amount of water evaporated, not time. Exam tip: The result that is measured or observed is usually the dependent variable.

Correct answer: C. The same

In an evaporation experiment, the initial amount of water is a variable that can affect the result. A larger volume generally provides more water to evaporate and may take a different amount of time than a smaller volume. If the starting volume changes from trial to trial, a difference in evaporation could be caused by volume rather than by the factor being tested, such as temperature. Therefore the initial volume should be kept the same in every trial, making option C correct.

The volume should also be measured accurately and recorded, while other relevant conditions, such as the container and observation time, are controlled as far as possible. Using different or doubled amounts would make the comparison unfair. Leaving the volume unrecorded prevents the researcher from checking whether the trials were comparable. Keeping it constant does not mean the volume is unimportant; it means its influence is controlled so the effect of the selected test factor can be judged fairly.

Correct answer: D. Correct interpretation of the result will be difficult

The direct answer is D: correct interpretation of the result will be difficult. In a fair experiment, only the independent variable should be changed; important other factors are controlled and kept the same. If a controlled variable changes too, it may also affect the outcome. Then we cannot tell whether the result was caused by the intended change or by the uncontrolled factor. A is wrong because an experiment will not always succeed. B is wrong because the independent variable does not disappear; the design simply becomes unreliable. C is wrong because measurements are still necessary. D correctly describes the loss of a fair comparison. Exam cue: two changing factors mean no clear cause.

Correct answer: A. What was changed what was measured and what was kept the same

The answer is A. To identify variables, first ask three simple questions: what did the experimenter change, what did the experimenter measure, and what was kept the same? The changed factor is the independent variable, the measured result is the dependent variable, and unchanged conditions are controlled variables. A states exactly this complete method, so it is correct. B, which colour is beautiful, is a personal opinion and has no experimental role. C, which result is preferred, describes a preference rather than a variable and can introduce bias. D, which instrument is new, concerns equipment age, not the three scientific roles; a new instrument could be controlled, independent, or irrelevant depending on the design. Memory cue: change, measure, keep same = independent, dependent, controlled.

Correct answer: A. The independent variable is changed the dependent variable is measured and controlled variables are kept the same

The independent variable is changed as the cause and the dependent variable is measured as the outcome. Controlled variables maintain fairness.

Correct answer: C. Independent variable

Soil depth is deliberately changed so it is the independent variable. In exams identify the factor changed by the experimenter.