Carbon-14 Dating: The radioactivity due to carbon-14 measured in a piece of a wooden casket from an ancient burial site is found to produce 20 counts per minute from a given sample, whereas the same amount of carbon from a piece of living wood produces 160 counts per minute. The half-life of carbon-14, a beta-minus emitter, is 5730 years. What would we calculate for the age of the artifact, assuming that the activity for living wood has remained constant over time?
A. 5700 years
B. 11,500 years
C. 14,800 years
D. 17,200 years
E. 23,000 years
Answer: D
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Which of the following materials is most appropriate for a design requiring a material with a high magnetic susceptibility that will be subjected to an alternating magnetic field of 60 Hz?
(a) Fe-3 wt. % Si (b) MnO (c) Alnico-5 (d) Fe3O4
Assume that all air properties may be evaluated at 27°C and determine the constants in the correlation equation: Nu = C (Gr Pr)m
A laboratory experiment has been performed to determine the natural-convection heat
transfer correlation for a horizontal cylinder of elliptical cross section in air. The
cylinder is 1-m-long, has a hydraulic diameter of 1 cm, a surface area of 0.0314 m2, and
is heated internally by electrical resistance heating. Recorded data include power
dissipation, cylinder surface temperature, and ambient air temperature. The power
dissipation has been corrected for radiation effects:
GIVEN
• A horizontal, elliptical cylinder in air
• Hydraulic diameter (Dh) = 1 cm = 0.01 m
• Length (L) = 1 m
• Cylinder surface area (As) = 0.0314 m2
• Experimental data for (Ts – T?) and q shown above FIND
• The constants in the correlation equation Nu = C(Gr Pr)m
ASSUMPTIONS
• All air properties may be evaluated at 27°C
SKETCH
PROPERTIES AND CONSTANTS
for dry air at 27°C
Thermal expansion coefficient (?) = 0.00333 1/K
Thermal conductivity (k) = 0.0256 W/(m K)
Kinematic viscosity (?) = 16.4 × 10–6 m2/s
Prandtl number (Pr) = 0.71
The wave-particle duality applies to
A) photons. B) electrons. C) protons D) all of the above E) none of the above
An air mass forming over the Gulf of Mexico would be classified as ______________
Fill in the blank(s) with correct word