If a 20 W laser beam, which has an initial diameter of 2.0 mm, spreads out to a diameter of 2.0 m after traveling 10,000 m, what is the final intensity of the beam?
a. 
b. 
c. 
d. 
e. 
d.
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The term hardness refers to the ability of a mineral to
a. resist scratching. b. break along definite smooth planes. c. break into equal-sized halves. d. scratch other minerals.
A point charge Q is placed on the x axis at x = 2.0 m. A second point charge, ?Q, is placed at x = 3.0 m. If Q = 40 ?C, what is the magnitude of the electrostatic force on a 30-?C charge placed at the origin?
A. 7.2 N B. 3.9 N C. 1.5 N D. 14 N E. 8.1 N
Gamma rays are photons with very high energy. How many visible-light photons with a wavelength of 500 nm would you need to match the energy of a gamma-ray photon with energy 4.1 × 10-13? (h = 6.626 × 10-34 J • s, c = 3.00 × 108 m/s)
A) 1.0 × 106 B) 1.4 × 108 C) 6.2 × 109 D) 3.9 × 103
Why is the bright yellow disk of the Sun, the photosphere, cooler than the areas both above and below it?
What will be an ideal response?