What makes a star shine?
A. nuclear fusion of light elements
B. radioactive decay of elements in its core
C. reflected light from the galaxy
D. nuclear fission of heavy elements
E. None of these choices is correct.
Answer: A
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A certain source of sound waves radiates uniformly in all directions. At a distance of 20 m from the source the intensity level is 51 db
What is the total acoustic power output of the source, in watts? (Note: The reference intensity I0 is 1.0 × 10-12 W/m2.)
Kepler's second law of planetary motion states "A line from a planet to the Sun sweeps over equal areas in equal intervals of ____."
a. time b. space c. arcs d. ellipses e. spheres
A transverse periodic wave is represented by the equation y(x, t) = 2.50 cm cos(2,500 rad/s t - 15.0
x). What is the direction of the velocity of the wave?
A. the + z direction B. the + y direction C. the + x direction D. the - z direction E. the - y direction F. the - x direction
Which of the following best describes what we mean by the focal plane of a telescope?
A) It is the upper surface of the telescope's primary lens or mirror. B) It is the place where, if we mounted film or an electronic detector, we could get a clear (not blurry) image of an object viewed through the telescope. C) It is the lower surface of the telescope's primary lens or mirror. D) It is the surface of the lens on the eyepiece, through which you would look to see objects in the telescope's field of view.