Variables in an experiment

The changed factor is independent the measured factor is dependent and the factor kept the same is controlled. This sequence is useful in exams.

The independent variable is the possible cause and the dependent variable is the outcome. Controlled variables ensure a fair comparison.

The amount of soap is deliberately changed so it is the independent variable. Foam height will be the measured outcome.

Direct answer: Option C is correct. The investigation tests the effect of soap amount, so soap amount is the independent variable and should be changed deliberately. Foam height is the measured dependent result. To make the comparison fair, the volume of water should remain the same in every trial. Reasoning: use equal water; change only the soap amount; measure the foam height; compare the results. Option A is wrong as the tested factor is supposed to vary, not remain constant. Option B is wrong because foam height is the result being measured. Option C works because equal water removes water volume as an alternative explanation, making the soap effect clearer. Option D is wrong because “measured result” is not a condition kept constant; it is the outcome recorded after each trial. Other relevant conditions, such as container and mixing method, may also need control. Memory cue: keep everything same except the factor being tested.

The researcher changes the duration of light, so it is the independent variable. In exams, identify the factor deliberately changed.

Plant height is the measured outcome of the experiment, so it is the dependent variable. Treat the measured result as the dependent variable.

Keeping the amount of sugar constant makes it a suitable controlled variable. Other conditions are kept constant for a fair test.

Bounce height is measured, so it is the dependent variable. The recorded outcome is the dependent variable.

The type of soil is deliberately changed, so it is the independent variable. Identify the factor being changed in the question.

The researcher changes the amount of soap, so it is the independent variable. The independent variable is controlled by the experimenter.

The rate of photosynthesis changes with light intensity and is measured. The outcome factor is the dependent variable.

Keeping the amount of water the same makes the test fair. Controlled variables prevent unwanted effects.

The type of surface is changed, so it is the independent variable. The independent variable forms the basis of comparison.

The time taken to turn sour is the measured result, so it is the dependent variable. It changes due to the independent variable.

Keeping the paper type the same allows only the effect of wing length to be tested. A controlled variable makes the experiment fair.

The dependent variable is the quantity that is measured to find out how it responds to a change. The independent variable is changed by the investigator, and controlled variables are kept the same. In a clear experiment, the measured result is often described as the effect, while the deliberately changed factor is described as the cause being tested.

In this case, the duration of exercise is changed. The pulse rate is then measured after or during the exercise to see how it responds. Thus exercise duration is the independent variable and pulse rate is the dependent variable. Pulse rate is not a constant or a controlled variable because it is the observed outcome. Therefore option D is correct.

The number of batteries is deliberately changed, so it is the independent variable. The changed factor is the independent variable.

The direct answer is B: the time of oscillation. In an experiment, the independent variable is the factor deliberately changed by the investigator, while the dependent variable is the result measured in response. Here, the lengths of the pendulums are different, so length is the changed factor. The time taken for oscillation is measured, so it is dependent on the chosen length. Option A, mass, is not the measured outcome and is not identified as the changing factor. Option B is correct because it is the recorded response. Option C, length, is the independent variable, not the dependent variable. Option D, thread colour, has no stated role and is irrelevant unless specifically tested. A useful rule is: ask, “What did I change?” for independent and “What did I measure?” for dependent.

The direct answer is C, the initial volume of liquid. The experiment tests how temperature affects evaporation rate, so temperature is the independent variable and evaporation rate is the dependent, measured variable. A fair test keeps other important conditions the same. Starting with equal liquid volumes helps ensure that a difference in evaporation is not simply caused by one container having more liquid. Step by step: change temperature; use equal initial volume; keep liquid type, exposed surface area, container, airflow and time comparable; measure evaporation rate; compare results. A is wrong because temperature is the factor deliberately changed. B is wrong because rate is the outcome being measured. C is correct because initial volume can be held constant. D is wrong because amount evaporated is a result or measurement, not a controlled condition in this wording. Other controls may also be needed, but among the given options C is suitable. Memory cue: a controlled variable is kept the same while the tested factor changes.

The number of nails attracted is measured, so it is the dependent variable. The variable representing the measured outcome is dependent.

The answer is A, amount of water. The independent variable is the factor deliberately changed by the investigator. Here, different amounts of water are given to the seeds, so water amount is the independent variable. The measured response is seedling length, making B the dependent variable, not the independent one. C, type of seed, should normally be kept the same so that seed type does not confuse the comparison; it is a controlled variable. D, amount of soil, should also be kept constant for a fair test and is another possible controlled variable. Thus the reasoning is: changed = water amount, measured = seedling length, kept same = seed type and soil amount. Memory cue: the independent variable is the experimenter’s chosen input; the dependent variable is the plant’s measured output.

The direct answer is B: reaction time. The independent variable is what the experimenter changes, and the dependent variable is what is measured as the response. In this investigation, sound intensity is deliberately changed. The person's reaction time is then measured to see whether it changes, so reaction time depends on sound intensity. Option A, sound intensity, is the independent variable, not the dependent variable. Option B is correct because it is the measured outcome. Option C, source of sound, may be kept the same or controlled, but it is not the stated response. Option D, age, is a characteristic of the person and may be controlled or recorded; it is not the quantity measured as the effect here. Always separate the input from the result: changed input is independent, measured result is dependent.

The size of the towel piece should remain the same for a fair comparison. Controlled variables improve reliability.

The slope angle is deliberately changed by the investigator, so it is the independent variable. The ball’s speed is the measured dependent variable.

The direct answer is A: size of the ice cube. In an experiment, the independent variable is the factor deliberately changed by the investigator. The dependent variable is the result measured, while controlled variables are kept the same so that the comparison is fair. Here the investigation asks how ice-cube size affects melting time. Step by step: choose different ice-cube sizes; keep other important conditions the same; measure the time each cube takes to melt; compare the times. Option A is correct because size is the factor intentionally varied. Option B is wrong because melting time is the dependent variable, the measured response to size. Option C is wrong as the independent variable because room temperature should normally be controlled or kept as similar as possible; changing it would introduce another cause. Option D is wrong because the material is ice in every trial and is not the factor being varied. The wording “effect of X on Y” is a useful clue: X is usually the independent variable and Y is usually the dependent variable. Memory cue: size changed, time measured.