The light-gathering power of a telescope is directly proportional to
a. the diameter of the primary mirror or lens.
b. the focal length of the primary mirror or lens.
c. the ratio of the focal lengths of its primary mirror or lens and its eyepiece.
d. the length of the telescope tube.
e. the diameter of the eyepiece.
a
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A CD has a diameter of 12.0 cm. If the CD starts from rest and has a constant angular acceleration of 2.0 
then the tangential velocity of a point 3.0 cm from the center of the CD after 3.0 sec is
A. 18 cm/s. B. 21 cm/s. C. 25 cm/s. D. 32 cm/s. E. 45 cm/s.
A.A B.B C.C D.D E. Toward the viewer F. Away from the viewer T. The field is zero.
Which of the following is a property of Seyfert galaxies?
A. Their nuclei have abnormally low luminosities. B. The radiation from their cores fluctuates rapidly. C. Most are elliptical galaxies. D. They contain no gas clouds.
Which situation has more energy, a H nucleus, or a separated proton and neutron?
A) A H nucleus, because work is required to put it together beginning from a separated proton and neutron. B) A H nucleus, because work is required to pull a H nucleus apart. C) A separated proton and neutron has more energy, because work is required to pull a H nucleus apart. D) A separated proton and neutron, because work is required to put a H nucleus together. E) They both have the same energy, because energy is always conserved in any physical process.