Some quasars show absorption spectra with a smaller redshift than their emission spectra. This indicates that
A) they are much closer than previously thought.
B) there is cooler gas between us and the quasar.
C) we still don't understand redshifts.
D) their black holes are still contracting.
E) their black holes are still expanding.
B
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Halley's comet orbits the Sun approximately every 76 years, therefore it is a short-period comet.
Answer the following statement true (T) or false (F)
Which of the following best summarizes what we mean by dark matter?
A) matter that we have identified from its gravitational effects but that we cannot see in any wavelength of light B) matter that may inhabit dark areas of the cosmos where we see nothing at all C) matter consisting of black holes D) matter for which we have theoretical reason to think it exists, but no observational evidence for its existence
An RL series circuit has: 4.8-mH coil, 2.8-? resistor, 1.0-V battery, ammeter and switch. After the switch is closed for a long time, find the final value of the current
a. 7.4E+1 A b. 3.6E–1 A c. 1.3E–2 A d. 2.8E+2 A e. 1.3E–2 A
The energy of a photon equals ______________ multiplied by the frequency
Fill in the blank(s) with correct word