The aurora borealis (northern lights) are caused by
a. sunlight reflecting from polar ice.
b. emissions from atoms and molecules in the upper atmosphere excited by electrons from the Sun.
c. thunderstorms.
d. an unknown process.
b
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A scalar quantity multiplied by a unit vector is a scalar quantity
Indicate whether the statement is true or false
The gravitational force in a molecular cloud depends on
A) density only. B) temperature only. C) density and temperature. D) composition. E) thermal pressure.
You lift a 10. lb physics book up in the air a distance of 1 ft, at a constant velocity of 0.5 ft/s. The work done by gravity is
A) +5 ft?lb. B) -10 ft?lb. C) -5 ft?lb. D) zero. E) +10 ft?lb.
A slab of material 1 rests on the surface of a slab of material 2 . A light ray in material 1 has an angle of incidence of 30° on the interface between the materials, while the ray in material 2 has an angle of refraction of 45°. What is the critical angle of incidence for total internal reflection for a ray of light going from material 2 to material 1?
a. 30° b. 45° c. In this case there is no critical angle. d. At least one of the indices of refraction or its equivalent is needed to solve this problem.