Why are massive stars more luminous than low mass stars? That is, why is there a mass-luminosity relation?
What will be an ideal response?
To understand the mass-luminosity relation, recall (1) the principle of hydrostatic equilibrium, which says that pressure balances weight, and (2) the pressure-temperature thermostat, which regulates energy production. A star that is more massive than the Sun has more weight pressing down on its interior, so the interior must have a higher pressure to balance that weight. That means the massive star's automatic pressure-temperature thermostat must keep the gas in its interior hot and the pressure high. A star less massive than the Sun has less weight on its interior and thus needs less internal pressure; therefore, its pressure-temperature thermostat is set lower. Massive stars are more luminous because they must make more energy to support their weight.
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The shepherd moons keep the ring particles in their rings by:
A) repelling the ring particles, causing them to slow down. B) repelling the ring particles, causing them to speed up or slow down. C) attracting the ring particles, causing them speed up. D) attracting the ring particles, causing them to speed up or slow down. E) both attracting and repelling the ring particles, causing them to speed up or slow down.
A projectile is launched with initial velocity v0 at an angle of 30° above the horizontal. If a second projectile is launched with the same initial velocity but at angle of 60° above the horizontal
A) The range of the second projectile will be twice that of the first. B) The range of the second projectile will be 1.41 that of the first. C) The range of the second projectile will be one-half that of the first. D) The ranges of the two projectiles will be identical. E) It is impossible to compare the ranges of the two projectiles.
A circular coil of wire of 200 turns and diameter 2.0 cm carries a current of 4.0 A. It is placed in a magnetic field of 0.70 T with the plane of the coil making an angle of 30° with the magnetic field. What is the magnetic torque on the coil?
A) 0.15 N ? m B) 0.088 N ? m C) 0.29 N ? m D) 0.40 N ? m E) 0.076 N ? m
A fish looks up through the smooth surface of the water at a bear directly above it. To the fish,
A. the bear appears to be exactly where it really is. B. the bear appears to be further away than it really is. C. the bear appears to be closer to the point directly above the fish than it really is. D. the bear cannot be seen due to total internal reflection.