How do we determine the amount of dark matter in elliptical galaxies?
A) We measure the broadening of the galaxy's absorption lines to infer the speeds of stars at different distances from the galactic center.
B) We measure how fast the galaxy rotates as a whole.
C) We measure the orbital velocities of star-forming gas clouds in the outer portion of the galaxy.
D) We count the number of stars in the galaxy. Combining this with the galaxy's volume, we can calculate the galaxy's density.
E) We search for dark lanes of dust and black holes within the galaxy.
A
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Using Equation 10-52 or 10-53, determine the approximate convective heat transfer coefficient for water boiling at atmospheric pressure in a container having a surface temperature of 130ºC. Compare this to a value obtained by using Equation 10-6.
Which of the following statements about electrons is not true?
A) Electrons orbit the nucleus rather like planets orbiting the Sun. B) Within an atom, an electron can have only particular energies. C) An electron has a negative electrical charge. D) Electrons have little mass compared to protons or neutrons. E) Electrons can jump between energy levels in an atom only if they receive or give up an amount of energy equal to the difference in energy between the energy levels.
Which gases within our atmosphere act as greenhouse gases?
a. water b. carbon dioxide c. oxygen and nitrogen d. all of the above e. a and b
The number of states in the He+ ion corresponding to the principle quantum number n = 5 are
a. 18 b. 25 c. 50 d. 9 e. 11