A group of students conducted an experiment to measure the electrical current produced by … — ACT

A group of students conducted an experiment to measure the electrical current produced by a monocrystalline silicon solar cell exposed to different wavelengths of light. For each trial, the cell was placed $30\text{ cm}$ from a light source, the light intensity at the source was kept constant at $500\text{ W/m}^2$ , and the cell temperature was maintained at $25^\circ\text{C}$ . The current output (in milliamperes, $\text{mA}$ ) was recorded for wavelengths ranging from $400\text{ nm}$ to $700\text{ nm}$ in increments of $50\text{ nm}$ .

Suppose the students want to conduct a follow-up experiment to determine how the distance from the light source affects the solar cell's current output when exposed to a single wavelength of light. Which of the following modifications to the procedure would allow the students to test this hypothesis?

A
Vary the distance from the light source from $15\text{ cm}$ to $60\text{ cm}$ while keeping the wavelength constant, and measure how the temperature of the cell changes.
B
Measure the current output at distances of $15\text{ cm}$ , $30\text{ cm}$ , $45\text{ cm}$ , and $60\text{ cm}$ while simultaneously increasing the wavelength of light at each distance.
Keep the wavelength, light intensity at the source, and cell temperature constant, and measure the current output at distances of $15\text{ cm}$ , $30\text{ cm}$ , $45\text{ cm}$ , and $60\text{ cm}$ .Answer
D
Keep the distance constant at $30\text{ cm}$ , vary the light intensity from $100\text{ W/m}^2$ to $500\text{ W/m}^2$ , and measure the current output at different wavelengths.

Answer

The correct modification is to keep the wavelength, light intensity at the source, and cell temperature constant, while measuring the current output at distances of

15\text{ cm}

30\text{ cm}

45\text{ cm}

, and

60\text{ cm}

The correct answer is the option that keeps the wavelength, light intensity at the source, and cell temperature constant, while measuring the current output at distances of

15\text{ cm}

30\text{ cm}

45\text{ cm}

, and

60\text{ cm}

. This is because a valid scientific experiment must isolate the independent variable of interest (distance) by varying it systematically while holding all other potential variables constant, and directly measuring the target dependent variable (current output).

Step-by-Step Solution

Identify the independent and dependent variables required by the new hypothesis.

The independent variable is the distance from the light source, and the dependent variable is the current output of the solar cell.

The hypothesis focuses on how distance affects current output, which dictates what must be varied and what must be measured.

Determine which variables must be controlled (held constant) in the modified experiment.

The wavelength of light, light intensity at the source, and cell temperature must remain constant.

Controlling these variables ensures that any observed changes in current output are solely due to the change in distance, rather than confounding factors.

Select the experimental procedure that matches these variables and controls.

The procedure must vary distance (

15\text{ cm}

60\text{ cm}

), measure current output, and keep wavelength, light intensity, and temperature constant.

This setup is the only one that establishes a valid control group and isolates the effect of the single independent variable.

Key Concept

Isolating a single independent variable and controlling all other experimental conditions to test a specific follow-up hypothesis.

Estimated Time:1m 30s

Question

Answer

Step-by-Step Solution

Key Concept

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