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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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
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?
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
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.