At every instant the ratio of the magnitude of the electric to the magnetic field in an electromagnetic wave in vacuum is equal to
a. the speed of radio waves.
b. the speed of light.
c. the speed of gamma rays.
d. all of the above.
e. only (a) and (b) above.
d
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A fast-moving body must have a larger acceleration than a slow-moving body
a. True b. False Indicate whether the statement is true or false
assume that the surface of the storage vessel has an absorptance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is 213.3 kJ/kg.
GIVEN
• A spherical vessel of liquid oxygen in a large black room
• Emittance of vessel surface (?) = 0.1
• Liquid oxygen temperature (To) = –183°C = 90 K
• Sphere diameter (D) = 0.3 m
• Room wall temperature (Tw) = 27°C = 300 K
• Heat of vaporization of oxygen (hfg) = 213.3 kJ/kg
FIND
(a) The rate of radiative heat transfer (qr) to the liquid oxygen in W (b) The rate of evaporation of oxygen (mo) in kg/s
ASSUMPTIONS
• Steady state prevails
• The temperature of the vessel wall is equal to the temperature of the oxygen
• Convective heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
The Stefan-Boltzmann constant (?) = 5.67 ? 10–8 W/(m2 K4)
The magnetic and rotational north poles on Earth are the same
Indicate whether the statement is true or false
Which has more skin?
A) an elephant B) a mouse C) both the same