What role does helium play in spectral classification?
What will be an ideal response?
It is ionized in the hottest O class stars, and prominent but neutral in B class stars; in cooler stars, it is not noted.
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If I0 = 10?12 W/m2 is the threshold of hearing, a sound with intensity I1 = 10?11 W/m2 will give a certain decibel level. Suppose a new sound has an intensity I2 = 2I12/I0 . What is the new decibel level?
a. 2.3 dB b. 23 dB c. 100 dB d. it will square the decibel level e. 1.0 dB
Your lungs hold 4.2 L of air at a temperature of 27°C and a pressure of 101.3 kPa. How many moles of air do your lungs hold? (R = 8.31 J/mol ? K)
A) 0.15 moles B) 0.17 moles C) 0.19 moles D) 0.21 moles E) 0.23 moles
This figure shows observations that have allowed astronomers to determine the orbits of several stars around Sgr A* (the central object). What can we learn about Sgr A* by analyzing these orbits?
A) its mass B) its age C) its chemical composition D) all of the above
A double-slit experiment is performed and then redone using slits of double the previous separation. Nothing else is changed. If the approximation sin 
holds, what happens to the angle between the maxima?
A. it stays the same B. it doubles C. it quadruples D. it halves E. it quarters