The cosmic background radiation has a low temperature today because
A. it has gotten so far from the Sun.
B. it was created with a low temperature.
C. the Universe has expanded, and expansion causes cooling.
D. all the stars that were heating it have burned out.
E. it is rich in heavy elements that absorb radiation very strongly.
Answer: C
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Compound Microscope: The objective lens and the eyepiece of a microscope have focal lengths of 4.0 mm and 25 mm, respectively. The objective produces a real image 30 times the size of the object, with the final image viewed at infinity. The near point of the microscope user is at 25 cm. What is the distance between the objective lens and the real image that it produces?
A. 116 mm B. 120 mm C. 124 mm D. 128 mm E. 132 mm
The angular speed of the hour hand of a clock, in rad/min, is
A.
.B.
.C.
.D.
E.
Einstein's special relativity is based upon two postulates. The most radical of the two postulates states that
A. the classical velocity addition formula still holds at relativistic speeds. B. there is no ether surrounding the Earth. C. the speed of light is finite. D. the speed of light is the same for all observers in all inertial reference frames.
Compounds tend to be ______________ compounds if they are formed from two or more nonmetals
a. covalent b. organic c. polar d. ionic