An astronomer obtains two samples of rarefied gas.She heats the first gas and finds that it produces a spectra with a series of bright lines.She places the other gas in front of a hot blackbody and finds a continuous spectrum with a series of dark lines.If the wavelengths of the dark lines are the same as those of the bright lines,she infers that the samples have identical:
A) reflectivity.
B) opacity.
C) compositions.
D) temperatures.

Question

Quizplus · Accepted Answer

The fact that the same wavelengths appear in both the bright line and dark line spectra suggests that the two samples contain the same atoms or molecules, and therefore have the same composition. This rules out choices A and D. The fact that the second sample produces a continuous spectrum with dark lines instead of bright lines suggests that the sample is absorbing certain wavelengths of light, which suggests that it has some level of opacity. Therefore, the best choice is B.

An Astronomer Obtains Two Samples of Rarefied Gas