Question

while researching a topic, a student has taken the following notes: - ethiopian student abebe was working on a garment suited for both warm and cold conditions. - he compared the emissivity (or ability to emit heat) of the materials he planned to use. - white thermal (heat reflective) metal fibers emitted almost no heat and had an emissivity of 0.02. - the thermal (heat absorbing) fibers absorbed large amounts of heat and had an emissivity of 0.74. - the amount of heat a material absorbs is equal to the amount of heat it emits.
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the student wants to contrast the emissivity of reflective metal fibers with that of silicon carbide fibers. which choice most effectively uses relevant information from the notes to accomplish this goal?
a the ability of reflective metal fibers and silicon carbide fibers to emit heat was determined by an analysis of each material’s emissivity.
b the amount of heat a material absorbs is equal to the amount it emits, as evidenced in abebe’s analyses.
c though the reflective metal fibers and silicon carbide fibers had different rates of emissivity, abebe planned to use both in a garment.
d whereas the reflective metal fibers had an emissivity of just 0.02, the silicon carbide fibers absorbed large amounts of heat, resulting in an emissivity of 0.74.

Explanation:

To contrast emissivity, we need to present the emissivity values of both materials (reflective metal fibers and silicon carbide fibers) and their heat absorption/ emission. Option D does this: it states reflective metal fibers have low emissivity (0.02) while silicon carbide fibers absorb heat (implying emission related to absorption, with emissivity 0.74), directly contrasting their emissivity using relevant info from notes (heat absorption - emission relation and emissivity values). Other options either don't contrast emissivity (A, B) or only mention different rates without values (C).

Answer:

D. Whereas the reflective metal fibers had an emissivity of just 0.02, the silicon carbide fibers absorbed large amounts of heat, resulting in an emissivity of 0.74.