A materials science research group conducted an experiment to analyze the photo-degradatio… — ACT

A materials science research group conducted an experiment to analyze the photo-degradation of polylactic acid (PLA) films. Four identical $0.5\text{ mm}$ thick PLA samples were placed into separate sealed test chambers, each maintained at a constant temperature of $25^\circ\text{C}$ and relative humidity of $50\%$ . Each sample was exposed to a different UV-C radiation intensity ( $2.0$ , $4.0$ , $6.0$ , and $8.0\text{ W/m}^2$ ) for 48 hours, after which the percentage reduction in sample mass was measured.

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

Independent variable: UV-C radiation intensity; Dependent variable: percentage reduction in sample massAnswer
B
Independent variable: percentage reduction in sample mass; Dependent variable: UV-C radiation intensity
C
Independent variable: UV-C radiation intensity; Dependent variable: chamber temperature
D
Independent variable: exposure time; Dependent variable: relative humidity

Answer

The independent variable is the UV-C radiation intensity, and the dependent variable is the percentage reduction in sample mass.

The correct response accurately pairs the manipulated condition (UV-C radiation intensity, changed between

2.0

and

8.0\text{ W/m}^2

) as the independent variable with the measured response (percentage reduction in PLA sample mass) as the dependent variable.

Step-by-Step Solution

Identify the factor directly manipulated by the researchers across the experimental conditions.

The researchers intentionally set different UV-C radiation intensities (

2.0

4.0

6.0

, and

8.0\text{ W/m}^2

) for each chamber. Therefore, UV-C radiation intensity is the independent variable.

The independent variable is the condition changed or manipulated by the experimenter.

Identify the observed outcome or measurement taken to determine the effect of the manipulation.

The outcome measured at the end of the 48-hour period is the percentage reduction in sample mass. Therefore, percentage reduction in sample mass is the dependent variable.

The dependent variable responds to changes in the independent variable and is the factor measured.

Distinguish independent and dependent variables from controlled parameters.

Chamber temperature (

25^\circ\text{C}

), relative humidity (

50\%

), exposure time (48 hours), and initial sample thickness (

0.5\text{ mm}

) are kept identical across all trials, making them controlled variables.

Controlled variables are held constant to ensure a fair test of cause and effect.

Key Concept

Classification of Independent, Dependent, and Controlled Variables

Estimated Time:1m 0s

Question

Answer

Step-by-Step Solution

Key Concept

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