Which of the following is true of wavelengths of signals sent into space?
A) Wavelengths longer than 100 cm are absorbed in Earth's atmosphere.
B) The interval between the 21-cm spectral line of neutral hydrogen and the 18-cm line of OH has very high background interference.
C) Wavelengths longer than 100 cm get lost in the background noise of the Milky Way Galaxy.
D) The interval between the 21-cm spectral line of neutral hydrogen and the 18-cm line of OH is narrow and can be monitored easily.
C
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Angular Momentum: Initially, a small 2.0-kg rock is whirling at the end of a very thin string in a circular path of radius 0.75 m on a horizontal frictionless surface, as shown in the figure. The initial tangential speed of the rock was 5.0 m/s. The string has been slowly winding around a vertical rod, and a few seconds later the length of the string has shortened to 0.25 m. What is the instantaneous speed of the mass at the moment the string reaches a length of 0.25 m?
A. 3.9 m/s B. 9.3 m/s C. 15 m/s D. 225 m/s E. 75 m/s
Exclusion Principle: The electron spin quantum number can have values of
A. -1/2, -1, 0, +1, +1/2. B. -1/2, -1, +1, +1/2. C. -1/2, 0, +1/2. D. -1/2, +1/2. E. only +1/2.
Which of the following types of electromagnetic radiation has the lowest energy?
a. X-rays b. visible light c. ultraviolet d. gamma rays e. infrared radiation
The most massive main-sequence stars are the ________ spectral class and the ________ luminosity class
Fill in the blank(s) with correct word