We can model a general cyanine-type dye molecule as if it contained N electrons trapped in a “box”-like potential energy function, where N is some even integer. The energy of a single quanton in a box is given by En = E1n2, where n is an integer and E1 is the energy of the ground (n = 1) energy level. If for a given molecule there are four electrons trapped in the molecule’s “box,” what is the lowest possible total energy of those electrons?
A. Etot = E1
B. Etot = 4E1
C. Etot = 8E1
D. Etot = 10E1
E. Etot = 30E1
D. Etot = 10E1
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Compare the rate of heat loss from a human body with the typical energy intake from consumption of food (4.325 MJ/day). Model the body as a vertical cylinder 30 cm in diameter and 1.8-m-high in still air. Assume the skin temperature is 2°C below normal body temperature. Neglect radiation, transpiration cooling (sweating), and the effects of clothing.
GIVEN
• Human body idealized as a vertical cylinder in still air
• Diameter (D) = 30 cm = 0.3 m
• Height (L) = 1.8 m
• Skin temperature (Ts) = 2°C below normal body temperature (37°C) = 35°C FIND
• Heat loss (q) and compare to consumption of food 4.325 MJ/day
ASSUMPTIONS
• Steady state
• Radiation, transpiration cooling, and clothing effects are negligible
• Ambient air temperature (T?) = 20°C
• Heat loss from the top of the cylinder is small compared to that from the sides
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 27.5°C
Thermal expansion coefficient (?) = 0.00333 1/°C
Thermal conductivity (k) = 0.0257 W/(m K)
Kinematic viscosity (?) = 16.4 × 10–6 m2/s
Prandtl number (Pr) = 0.71
A simple pendulum, 2.0 m in length, is released from rest when the support string is at an angle of 25° from the vertical. What is the speed of the suspended mass at the bottom of the swing?
Experienced players can throw a Frisbee so it skips off the ground (the Frisbee’s front edge actually tips upward after the Frisbee hits, enabling it to climb back into the air). If a right-handed player throws a Frisbee in the usual way, it rotates counterclockwise when viewed from above. To skip the Frisbee, which edge has to hit the ground (as seen by the thrower)? (Hint: The Frisbee’s angular momentum vector, and thus its rotation axis, changes in the direction of the external torque that the strike applies to the Frisbee.)
A. The back edge B. The front edge C. The right edge D. The left edge E. The entire rim must hit the ground simultaneously.
Quantum field theory arises out of the combination of
A) quantum theory and nuclear physics. B) the general theory of relativity and quantum theory. C) the special theory of relativity and the theory of electromagnetism. D) the special theory of relativity and quantum theory. E) quantum theory and the big bang theory of the creation of the universe.