An insulator has a positive electric charge of 2.4 × 10^ -17 C. How many electrons were added or removed?
150 electrons removed
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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
An up quark (u) has a charge of +2/3 and a down quark (d) has a charge of ?1/3. Which of the following describes a neutron?
A) uuu B) uud C) udd D) ddd
Light from inside a raindrop that exits into the air
A) slows down. B) remains at speed c. C) speeds up. D) none of the above
Francium-223 decays to radium-223 by emitting what kind of nuclear radiation?
A) Alpha B) Beta minus C) Beta plus D) Gamma E) X-rays.