Variables in an experiment

The time to reach the ground is measured, so it is the dependent variable. Drop height is the independent variable.

The answer is C, volume of water. The question asks for a controlled variable, so we need a condition kept the same while salt concentration is changed. Keeping the water volume constant makes the comparison fair and helps isolate the effect of salt concentration. A, salt concentration, is the independent variable because it is deliberately changed. B, whether the egg floats, is the dependent outcome being observed. C is correct because water volume is held constant. D, solution density, is affected by the salt concentration and is closely related to the experimental effect, so it should not be selected as the controlled factor here; it may be a measured or resulting property. The fair-test chain is: change salt concentration, observe floating, keep water volume the same. Do not choose the outcome as a control.

The test score is the measured outcome that may change when the amount of study time changes. Therefore, it is the dependent variable.

The independent variable is the factor that the investigator deliberately changes to study its effect. The dependent variable is the result that is observed or measured. Other important conditions, such as cloth size and initial water amount, should usually be kept the same so that the comparison is fair.

In this experiment, the researcher changes the fan speed and measures how long the wet cloth takes to dry. Thus fan speed is the independent variable, so option A is correct. Drying time is the dependent variable because it responds to the change in fan speed. Cloth size and amount of water may be controlled variables if they are kept constant. Changing only the selected factor makes it easier to judge its effect on drying.

The dependent variable is the quantity measured to find out how the independent variable affects the system. The independent variable is changed deliberately, while controlled variables, such as the amounts of other materials, should be kept fixed. Identifying these roles helps make the experiment a fair test.

In this investigation, temperature is changed from one trial to another. The gas produced by yeast is then measured as the response. Therefore, the amount of gas produced is the dependent variable, making option B correct. Temperature is the independent variable. The amount of yeast and sugar should normally remain the same in each trial; they are not the measured outcome.

The duration of light should remain the same so that only colour is tested. A controlled variable ensures fair comparison.

Electrical resistance is the outcome measured after changing the length of the wire. Hence, resistance is the dependent variable because its value depends on the independent variable, the wire length. Controlled variables are kept unchanged, such as the material, thickness, and temperature of the wire. Exam tip: the quantity changed is the independent variable, while the measured result is the dependent variable.

The direct answer is A: thickness of the thread. The independent variable is the factor deliberately changed to study its effect. Here, the investigation asks how thread thickness affects the load supported before breaking, so thickness is changed from one trial to another. The supported load is the observed result and is therefore the dependent variable. Option A is correct. Option B, supported load, is dependent because it is measured at breaking. Option C, thread length, should normally be kept constant as a controlled variable unless the investigation is specifically about length. Option D, material, should also be kept the same for a fair comparison; changing it would introduce another factor. The experiment must change thickness while keeping other important conditions alike. Exam cue: “effect of X on Y” usually means X is independent and Y is dependent.

The percentage of stain removed is the measured outcome, so it is the dependent variable. Detergent amount is the independent variable.

A controlled variable is a condition that is kept the same while the independent variable is changed and the dependent variable is measured. Keeping such conditions constant makes the comparison fair. In this investigation, the purpose is to observe how water temperature changes with time while the container is placed in sunlight.

The time in sunlight is the factor being varied or observed, and water temperature is the measured dependent quantity. Change in temperature is also part of the result, not a controlled condition. The container size can be kept identical for every trial, so it is a controlled variable. Therefore, option C is correct. If container sizes differed, they could affect heating and make it difficult to attribute the temperature change only to time.

The direct answer is D, the independent variable. The independent variable is the factor that the experimenter deliberately changes. In this investigation, the amount of food is changed and fish growth is measured. Therefore food amount is the input or possible cause, while growth is the response. Step by step: choose different food amounts; keep fish type, number, water conditions, temperature, tank size and time as similar as possible; measure growth; compare growth between amounts; so food amount is independent. A is wrong because dependent variable means the measured response, here fish growth. B is wrong because “outcome variable” also refers to a result, not the changed food amount. C is wrong because a controlled variable is kept unchanged, whereas food quantity is intentionally varied. D is correct. A useful distinction is: independent = what I change; dependent = what I measure; controlled = what I keep the same. Memory cue: the cause is independent, the effect is dependent.

The type of insulating material is changed, so it is the independent variable. Cooling time is the dependent variable.

The electric current is the quantity being measured as the distance changes, so it is the dependent variable. The distance is the independent variable that is deliberately changed.

The tablet size should be kept the same so that only temperature is tested. This makes the experiment fair.

The number of words remembered is the measured result, so it is the dependent variable. Sleep duration is the independent variable.

Acid concentration is deliberately changed, so it is the independent variable. Reaction rate is the dependent variable.

In an experiment, the dependent variable is the result that is observed or measured. The independent variable is the factor deliberately changed to investigate its effect. In this investigation, candle length is changed or compared, while the time for which each candle burns is recorded. The recorded burning time may therefore depend on the selected candle length, provided other important conditions are kept as similar as possible.

Option B is correct because burning time is the measured outcome. Candle length is the independent variable, not the dependent one. Candle colour and wick thickness are not identified as the measured result in the question; they would need to be controlled or kept consistent if they could affect burning. The key test is to ask, “What is being measured?” Here, the answer is the time taken to burn.

The size of the object should remain the same so that only liquid type is tested. It is a controlled variable.

In an experiment, the independent variable is deliberately changed, while the dependent variable is measured to see the effect of that change. A controlled variable is kept constant so that it does not interfere with the comparison. Identifying these roles depends on what the investigator changes and what result is recorded, not simply on the wording of the variable.

Here, the volume of music is changed by the investigator. Reading speed is then measured to find out whether the music volume affects it. Therefore, reading speed is the dependent variable, making option D correct. It is not the independent or changed variable in this setup; those descriptions apply to music volume. Conditions such as the reading material and available time could be controlled if needed.

Water depth is changed to observe its effect, so it is the independent variable. Light availability is the dependent variable.

The amount of runoff is the measured result, so it is the dependent variable. Water added is the independent variable.

The experiment is designed to find out how temperature affects the extension of a rubber band. Temperature is therefore the independent variable, and extension length is the measured dependent variable. To make the comparison fair, another important factor that could affect extension must remain unchanged.

The applied load should be kept constant. If different loads were used at different temperatures, a change in extension could be caused by the load rather than by temperature, or by both together. Keeping the same rubber band and the same load allows the effect of temperature to be compared more fairly. Thus option C is correct. Temperature cannot be the controlled variable here because it is the factor being deliberately changed.

The light-meter reading is observed and recorded after the distance is changed. Since it responds to the changed distance, the reading is the dependent variable.

The governing concept is experimental variable classification. The independent variable is the factor deliberately changed to investigate its effect. Here the investigator compares parachutes of different sizes, so parachute size is the independent variable and option A is correct. Falling time is the measured response, making it the dependent variable. Drop height and suspended mass should normally be kept constant so that they do not provide alternative explanations for differences in falling time; they are controlled variables. If either were changed as well, the test would no longer isolate the effect of parachute size. A fair comparison therefore changes size alone and records repeated falling times.

The direct answer is B: drainage time. The amount of sand is deliberately changed, so it is the independent variable. The time taken for water to drain is then measured and may change because of that sand amount; it is therefore the dependent variable. A is wrong because it is the manipulated input, not the measured result. C is a sensible controlled variable: starting water volume should normally be the same so the comparison is fair. D, total soil mass, may also need control or careful definition, but it is not the requested measured outcome. Follow the chain: change sand amount, pour equal water, measure drainage time. The final measurement is dependent. Memory cue: the result that responds is dependent.