How do we learn about what is going on in the center of our own galaxy (the Milky Way)?
A) We have learned it only recently, thanks to the great photographs obtained by the Hubble Space Telescope.
B) We cannot see the galactic center with visible or ultraviolet light, but radio and X-rays from the center can be detected.
C) The gas and dust in the Milky Way prevent any type of direct observation of the galactic center, but theoretical models allow us to predict what is happening there.
D) We must look at the centers of other galaxies and hope that ours is just like others.
E) We can study it with visible telescopes as with any other star in the Galaxy.
B
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Which of the Terrestrial planets is considered a "water world"?
a. Mercury b. Venus c. Earth d. Mars e. Neptune
Why do astronomers think Miranda has such an unusual surface?
A) It underwent an episode of tidal heating in the past. B) It was squashed by a giant impact. C) It formed from the remains of a giant impact relatively recently. D) Its surface is covered with a powdery dust from micrometeorite impacts. E) Its low temperature affects the colors of its surface ice.
Calculate the rate of heat loss per foot and the thermal resistance for a 15 cm schedule 40 steel pipe covered with a 7.5 cm thick layer of 85% magnesia. Superheated steam at 150°C flows inside the pipe [ ch = 170 W/(m2 K)] and still air at 16°C is on the outside [ ch = 30 W/(m2 K)].
GIVEN
A 6 in. standard steel pipe covered with 85% magnesia Magnesia thickness = 15 cm=0.15 m Superheated steam at Ts= 150°C flows inside the pipe Surrounding air temperature (T?) = 17°C Heat transfer coefficients
? Inside ( ci h ) = 170 W/(m2 K)
? Outside ( co h ) = 30 W/(m2 K)
FIND
(a) The thermal resistance (R) (b) The rate of heat loss per foot (q/L)
ASSUMPTIONS
Constant thermal conductivity The pipe is made of 1% carbon steel
SKETCH
PROPERTIES AND CONSTANTS
? Inside diameter (Di) = 6.065 in.=0.154 m
? Outside diameter (Do) = 6.625 in.=0.1683 m Thermal Conductivities
? 85% Magnesia (kI) = 0.059 W/(m K) at 20°C
? 1% Carbon steel (ks) = 43 W/(m K) at 20°C
Scattered light in the atmosphere is often partially polarized. The best way to determine whether or not light from a particular direction in the sky shows polarization is to
a. diffract the light through a single slit. b. squint while looking in that direction. c. rotate a piece of polaroid film about an axis parallel to the ray while looking through it in that sky direction. d. rotate a piece of polaroid film about an axis perpendicular to the ray while looking through it in that sky direction. e. reflect the rays from that direction on a shiny metal surface.