A materials scientist investigated how the average pore diameter of polyurethane acoustic … — ACT

A materials scientist investigated how the average pore diameter of polyurethane acoustic foam panels affects their sound absorption performance. Four foam panels of identical thickness ( $50\text{ mm}$ ) were tested in a sound chamber at a constant ambient temperature ( $22^\circ\text{C}$ ) and fixed incident sound frequency ( $1,000\text{ Hz}$ ). The experimental conditions and measured outcomes are summarized in the table below:

Panel	Panel Thickness ( $\text{mm}$ )	Average Pore Diameter ( $\mu\text{m}$ )	Sound Absorption Coefficient ( $\alpha$ )
1	50	200	0.42
2	50	400	0.65
3	50	600	0.81
4	50	800	0.73

Which of the following correctly identifies the independent variable and the dependent variable in this investigation?

Independent variable: Average pore diameter; Dependent variable: Sound absorption coefficientAnswer
B
Independent variable: Sound absorption coefficient; Dependent variable: Average pore diameter
C
Independent variable: Incident sound frequency; Dependent variable: Sound absorption coefficient
D
Independent variable: Average pore diameter; Dependent variable: Ambient temperature

Answer

The independent variable is the average pore diameter of the foam panel, and the dependent variable is the sound absorption coefficient.

In experimental design, the independent variable is the factor modified systematically by the researcher to determine its effect, which in this study is the average pore diameter (

200

800\ \mu\text{m}

). The dependent variable is the quantitative result measured to observe that effect, which here is the sound absorption coefficient (

\alpha

Step-by-Step Solution

Identify the variable that the researcher intentionally changes or manipulates between experimental groups.

The researcher systematically varied the average pore diameter (

200\ \mu\text{m}

400\ \mu\text{m}

600\ \mu\text{m}

, and

800\ \mu\text{m}

) across Panels 1–4. Thus, average pore diameter is the independent variable.

The independent variable is the factor controlled and changed by the experimenter to test its effects.

Identify the variable being measured to observe the effect of the manipulated variable.

The researcher recorded the resulting sound absorption coefficient (

\alpha

) for each panel. Thus, the sound absorption coefficient is the dependent variable.

The dependent variable represents the experimental outcome or response being measured.

Distinguish independent and dependent variables from controlled variables.

Panel thickness (

50\text{ mm}

), ambient temperature (

22^\circ\text{C}

), and incident sound frequency (

1,000\text{ Hz}

) were kept identical across all trials, confirming they are controlled variables.

Controlled variables must remain constant so that any observed changes in the dependent variable can be attributed solely to the independent variable.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

Estimated Time:1m 0s

Question

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Step-by-Step Solution

Key Concept

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