A 7.5 × 1014 Hz laser emits a 7.7-?s pulse, 5.0 mm in diameter, with a beam energy density of 0.51 J/m3. What is the amplitude of the electric field of the emitted waves? (c = 3.00 × 108 m/s, ?0 = 4? × 10-7 T ? m/A, ?0 = 8.85 × 10-12 C2/N ? m2)
A) 340 kV/m
B) 480 kV/m
C) 240 kV/m
D) 150 kV/m
E) 120 kV/m
Answer: A
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A) population II stars in the Halo. B) dark matter out in the Halo. C) population I stars in the disk. D) hydrogen gas in the disk and spiral arms. E) the black hole in the Galactic Center.
Successive bright fringes in an interference pattern result from
A) equal-length distances from the slits. B) distance from the slits successively increasing one wavelength at a time. C) destructive interference. D) none of the above
Atmospheric lifting resulting from the convergence of two different air masses is called
A) convectional lifting. B) orographic lifting. C) adiabatic lifting. D) frontal lifting.
What is a black hole?
A. a binary star B. a product of our imagination C. massive collapsed stars with strong gravitational fields D. massive collapsed stars with strong electromagnetic fields