A main-sequence star more massive than the Sun:
A) will have less density than the Sun.
B) will have more luminosity than the Sun.
C) always undergoes proton-proton chain reactions to generate energy.
D) always undergoes carbon-nitrogen-oxygen cycle to generate energy.
B
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What is thought to be the origin of enormous x-ray flares that occasionally come from the direction of Sgr A*?
A) x-ray binary systems that lie close to the galactic center B) massive-star supernovae near the galactic center C) comet-sized objects being torn apart by the tidal forces of the black hole near the galactic center D) supernova shock waves plowing into dense regions of the interstellar medium near the galactic center
The unit for rate of energy transformation, the watt, in an electric circuit is equivalent to which of the following?
a. A×W c. V/W b. V/s d. V×A
Show that the rate of heat conduction per unit length through a long hollow cylinder of inner radius ri and outer radius ro, made of a material whose thermal conductivity varies linearly with temperature, is given by
GIVEN
• A long hollow cylinder
• The thermal conductivity varies linearly with temperature
• Inner radius = ri
• Outer radius = ro FIND
• Show that the rate of heat conduction per unit length is given by the above equation ASSUMPTIONS
• Conduction occurs in the radial direction only
• Steady state prevails
SKETCH
Two cylindrical resistors are made of the same material and have the same resistance. The resistors, R1 and R2, have different radii, r1 and r2, and different lengths, L1 and L2 . Which of the following relative values for radii and lengths would result in equal resistances?
a. r1 = r2 and 4L1 = L2 c. 2r1 = r2 and 4L1 = L2 b. r1 = r2 and L1 = 2L2 d. 2r1 = r2 and L1 = 2L2