Atmospheric scientists conducted an experiment to evaluate how varying the ambient relativ… — ACT

Atmospheric scientists conducted an experiment to evaluate how varying the ambient relative humidity ( $\text{RH}$ , measured as a percentage) influences the crystallization time (in seconds) of acoustically levitated ammonium sulfate ( $(\text{NH}_4)_2\text{SO}_4$ ) microdroplets. Throughout all trials, the ambient temperature was held constant at $20.0^\circ\text{C}$ and the initial droplet radius was held constant at $5.0\,\mu\text{m}$ .

Match each experimental component from the investigation to its corresponding variable classification.

Ambient relative humidity ( $\text{RH}$ )Independent Variable
Microdroplet crystallization timeDependent Variable
Initial droplet radius ( $5.0\,\mu\text{m}$ ) and temperature ( $20.0^\circ\text{C}$ )Controlled Variables

Answer

Ambient relative humidity matches Independent Variable; Microdroplet crystallization time matches Dependent Variable; Initial droplet radius (

5.0\,\mu\text{m}

) and temperature (

20.0^\circ\text{C}

) match Controlled Variables.

In experimental design, the independent variable is the factor explicitly manipulated by researchers (ambient relative humidity). The dependent variable is the outcome measured in response to that manipulation (microdroplet crystallization time). Controlled variables are baseline conditions held constant throughout all trials (initial droplet radius and ambient temperature) to ensure observed differences stem solely from the independent variable.

Step-by-Step Solution

Determine which factor is manipulated by the experimenter (Independent Variable).

The ambient relative humidity (

\text{RH}

) is intentionally varied across trials.

The independent variable is the condition systematically changed to test its effect.

Determine which factor is measured as the experimental outcome (Dependent Variable).

The crystallization time of the microdroplets is measured in response to humidity changes.

The dependent variable is the quantitative response observed during the experiment.

Determine which factors are kept identical across all test conditions (Controlled Variables).

Initial droplet radius (

5.0\,\mu\text{m}

) and ambient temperature (

20.0^\circ\text{C}

) are held constant.

Controlled variables are fixed to isolate the relationship between independent and dependent variables.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

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