The brightest 100 stars viewed from Earth are mostly not on the main sequence (even though most stars are) because:
A. only high mass stars formed near us in the Galaxy.
B. our region of the Galaxy is very young.
C. the most luminous stars are giants and supergiants that have already finished their main sequence lifetimes.
D. the main sequence is the shortest part of a star's life, so stars don't spend much time there.
E. our region of the Galaxy is very old.
Answer: C. the most luminous stars are giants and supergiants that have already finished their main sequence lifetimes.
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The magnetic field lines inside a bar magnet go in what direction?
A. from south pole to north pole B. from north pole to south pole C. from side to side D. There are no magnetic field lines inside a bar magnet.
The particles in the nucleus referred to as nucleons are
A. electrons and protons. B. protons and neutrons. C. neutrons and electrons. D. electrons and photons.
The human eye can just detect green light of wavelength 500 nm if it arrives at the retina at the rate of 2 × 10-18 W
How many photons arrive each second? (c = 3.0 × 108 m/s, h = 6.626 × 10-34 J ? s)
Two long straight wires carry currents perpendicular to the xy plane. One carries a current of 50 A and passes through the point x = 5.0 cm on the x axis. The second wire has a current of 80 A and passes through the point y = 4.0 cm on the y axis. What is the magnitude of the resulting magnetic field at the origin?
a. 200 ?T b. 600 ?T c. 450 ?T d. 300 ?T e. 400 ?T