A team of materials engineers conducted an experiment to evaluate how different zirconium … — ACT

A team of materials engineers conducted an experiment to evaluate how different zirconium dioxide ( $\text{ZrO}_2$ ) additive concentrations in ceramic heat-shield tiles affect peak thermal conductivity under simulated re-entry conditions. In each trial, ceramic tiles of identical dimensions were exposed to a $1200^\circ\text{C}$ plasma jet at a constant chamber atmospheric pressure of $1.0\text{ atm}$ for exactly 300 seconds. Match each experimental component to its correct variable classification.

$\text{ZrO}_2$ additive concentration ( $0\%, 5\%, 10\%, 15\%$ )Independent Variable
Peak thermal conductivity of the ceramic tileDependent Variable
Chamber atmospheric pressure ( $1.0\text{ atm}$ )Controlled Variable

Answer

\text{ZrO}_2

additive concentration corresponds to the Independent Variable; Peak thermal conductivity corresponds to the Dependent Variable; Chamber atmospheric pressure corresponds to the Controlled Variable.

In scientific investigations, the independent variable is the parameter systematically changed by the experimenter to test its effect (the

\text{ZrO}_2

concentration). The dependent variable is the measurable result or response observed (peak thermal conductivity). Controlled variables are all conditions held constant across trials (such as the chamber pressure of

1.0\text{ atm}

, plasma temperature, exposure time, and tile size) to prevent confounding factors from influencing the outcome.

Step-by-Step Solution

Identify the variable that is systematically varied or manipulated by the experimenter.

The researchers explicitly change the

\text{ZrO}_2

additive concentration (

0\%, 5\%, 10\%, 15\%

) across test trials, establishing it as the independent variable.

The independent variable is the cause or factor directly controlled and varied by the researchers.

Identify the variable that is observed and measured to quantify the effect of the manipulation.

Peak thermal conductivity is recorded during exposure to determine how it responds to changes in

\text{ZrO}_2

concentration, establishing it as the dependent variable.

The dependent variable represents the effect or measured response resulting from changes in the independent variable.

Identify experimental conditions that are held constant throughout all trials.

Chamber atmospheric pressure (

1.0\text{ atm}

), plasma jet temperature (

1200^\circ\text{C}

), exposure time (300 seconds), and tile dimensions are held identical across all tests, establishing them as controlled variables.

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

Key Concept

Identifying Independent, Dependent, and Controlled Variables

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