The intensity level of a power mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are mowing their lawn 20 m from your open bedroom window. What is the intensity level in your bedroom?
A)
80 dB
B)
104 dB
C)
400 dB
D)
50 dB
E)
40 dB
A
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If observations had shown that the cosmic microwave background was perfectly smooth (rather than having slight variations in temperature), then we would have no way to account for
A) the relationship between the strong and the weak force. B) the fact that our universe is expanding. C) how galaxies came to exist. D) the existence of helium in the universe.
A uniform linear charge of 2.0 nC/m is distributed along the x axis from x = 0 to x = 3 m. Which of the following integrals is correct for the y component of the electric field at y = 4 m on the y axis?
A.
B.
C.
D.
E.
How fast must a hydrogen atom be traveling for its kinetic energy to be just enough to excite the ground-state atom to its first excited state in a collision? (1 eV = 1.60 × 10-19 J, mH ? mproton = 1.67 × 10-27 kg)
A) 66.5 km/s B) 21.7 km/s C) 44.2 km/s D) 113 km/s E) 51.0 km/s
You want to confine an electron in a box (an infinite well) so that its ground state energy is 5.0 × 10-18 J. What should be the length of the box? (h = 6.626 × 10-34 J ? s, mel = 9.11 × 10-31 kg)
A) 0.11 nm B) 0.22 nm C) 0.15 nm D) 0.18 nm