Magnetic fields are produced by
a. constant electric currents.
b. electric currents that vary sinusoidally with time. c. time-varying electric fields.
d. all of the above. e. only (a) and (b) above.
D
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Intensity of Sound: A certain siren radiates sound uniformly in all directions. At a distance of 17 m from the siren, the intensity level is 49 db. How many watts of power does this siren put out? The threshold of human hearing is 1.0 × 10-12 W/m2.
Fill in the blank(s) with the appropriate word(s).
If energy is released when the parts of a system are allowed to disperse to infinity, its binding energy is
A. Positive. B. Negative. C. Zero. D. Not defined in such a case.
The microwave in the kitchen has a label that indicates it produces its microwaves at a frequency of 2450 MHz. What is the energy associated with one of these microwave photons? (h = 6.63 × 10^?34 J?s)
a. 3.19 × 10^–2 eV b. 2.45 eV c. 1.02 × 10^–5 eV d. 1.62 eV
White light is shone on a very thin layer of mica (n = 1.57). When the mica layer is observed from the illuminated side, interference maxima for wavelengths of blue (480 nm) and yellow (560 nm) are observed. What is the thickness of the mica layer?
A. 1.58 ?m B. 0.79 ?m C. 3.16 ?m D. insufficient information is given.