Glowing in the Dark

question 245

Multiple Choice

Glowing in the Dark
Have you ever wondered how glow-in-the-dark things actually glow in the dark? Most glow-in-the-dark items glow because of something called phosphorescence or photoluminescence. Phosphorescent items must be "charged" under a bright light before they actually glow in the dark. This charging process works because of a substance called phosphor.
When light from the sun or a lamp hits phosphor, the phosphor molecules absorb the light and become energized. As the phosphor molecules release the stored energy, they emit a dim light that is visible in the dark. The color of the light that they produce depends on the color of the dye added to the glow-in-the-dark item. Usually, green dye is added to the phosphors to make the light easier to see. Although any color can be used, the human eye sees green light most clearly in the dark.
There are also a few glow-in-the-dark items that do not need to be charged. Emergency exit signs, gun sights, and certain kinds of expensive wristwatches glow because of radioluminescence. In these items, the phosphor is mixed with a radioactive element called tritium. The radiation from the tritium provides energy to the phosphor. It is almost as if there are thousands of tiny lamps constantly shining on the phosphor. Because their phosphor is always energized, these radioluminescent items are always glowing.
One other kind of glow-in-the-dark item that does not require charging is the glow stick. Glow sticks do not need to be held under light and do not contain any radioactive elements. Instead, glow sticks glow using chemiluminescence. Glow sticks contain a fluorescent dye and a thin glass tube that contains a chemical. To activate a glow stick, you bend the plastic container, causing the glass to break. The chemical inside the glass then mixes with the dye. The combination of the chemical and the dye produces visible light.
Question: Which of the following can be inferred from the passage?

• A)Phosphorescent objects that are kept in complete darkness for a long time will not glow.
• B)All phosphorescent objects contain some kind of radioactive element.
• C)Photoluminescent objects can only glow green, red, and yellow.
• D)The chemical substances found in some photoluminescent objects is hazardous to human health.

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Definitions:

Independent Variable

The variable in an experimental setting that is manipulated to observe its effect on a dependent variable.

Random Error

Variability in data that arises from unpredictable fluctuations in the measurement process.

Null Hypothesis

A statement in statistics that proposes there is no significant effect or difference between specified populations, any observed difference being due to sampling or experimental error.

Observed Difference

The apparent discrepancy or variation between two groups or conditions in an experiment or study.